Wednesday, 30 December 2009

Restore a database using TSQL

To restore a database use the following SQL:

USE [tempdb]
ALTER DATABASE [DatabaseName]

SET SINGLE_USER WITH
ROLLBACK IMMEDIATE
GO

RESTORE DATABASE [DatabaseName]
FROM DISK = 'C:\BackupName.BAK'
WITH MOVE 'MDF_logical_name' TO 'C:\MDFName.mdf',
MOVE 'LDF_logical_name' TO 'C:\LDFName.ldf'
GO

ALTER DATABASE [DatabaseName] SET MULTI_USER
GO

Note that this puts the database into single user mode first (i.e. it kicks off other users). Don’t forget the USE [tempdb] statement or you may find the database still in use and the restore may fail. If you’re doing a straight restore you can get the logical filenames etc. from the backup file:

RESTORE FILELISTONLY FROM DISK = 'C:\BackupName.BAK'
GO

Wednesday, 16 December 2009

Keyboard shortcuts for Remote Desktop sessions

  • CTRL+ALT+END: Open the Microsoft Windows NT Security dialog box (CTRL+ALT+DEL)
  • ALT+PAGE UP: Switch between programs from left to right (CTRL+PAGE UP)
  • ALT+PAGE DOWN: Switch between programs from right to left (CTRL+PAGE DOWN)
  • ALT+INSERT: Cycle through the programs in most recently used order (ALT+TAB)
  • ALT+HOME: Display the Start menu (CTRL+ESC)
  • CTRL+ALT+BREAK: Switch the client computer between a window and a full screen
  • ALT+DELETE: Display the Windows menu
  • CTRL+ALT+Minus sign (-): Place a snapshot of the entire client window area on the Terminal server clipboard (ALT+PRT SC)
  • CTRL+ALT+Plus sign (+): Place a snapshot of the active window in the client on the Terminal server clipboard (PRT SC)

User-defined Functions in SQL Server

User-defined functions (UDFs) encapsulate logic for use in other queries. Views are limited to a single SELECT statement but user-defined functions can have multiple SELECT statements.

There are basically 3 categories of UDF:

  • Scalar-valued function
    • Returns a single, scalar value.
    • Can be used as column name in queries.
    • Can contain an unlimited number of statements as long as only one value is returned.
  • Inline function
    • Returns a variable of data type table.
    • Can only contain a single SELECT statement.
    • The structure of the returned value is generated from the columns that compose the SELECT statement.
    • A table variable need not be explicitly declared and defined.
  • Table-valued function
    • Can contain any number of statements that populate the table variable to be returned.
    • Useful when you need to return a set of rows.
    • A table variable must be explicitly declared and defined.
    • An advantages over a view is that the function can contain multiple SQL statements whereas a view is composed of only one statement.

Differences between Stored Procedures and UDFs:

  • UDF can be used in SQL statements whereas SPs can’t.
  • UDFs that return tables can be treated as another rowset and can be used in JOINs.
  • Inline UDF's can be thought of as views that take parameters and can be used in JOINs etc.

Monday, 14 December 2009

Model-View-ViewModel (MVVM) pattern

MVVM is gaining considerable traction in the WPF and Silverlight communities. The MVVM pattern can be said to be a specialisation of Fowler’s Presentation Model pattern.

The essence of a Presentation Model is of a fully self-contained class that represents all the data and behavior of the UI window, but without any of the controls used to render that UI on the screen. A view then simply projects the state of the presentation model onto the glass.

There is also some similarity with the Model-View-Presenter (MVP) pattern, with the ViewModel being roughly analogous to the Presenter.  However, unlike MVP the ViewModel doesn’t need a reference to the View – the view uses data binding to be made aware of changes. The ViewModel and not the View performs all modifications made to the model data.

Some features of MVVM:

  • View classes are unaware of Model classes
  • ViewModel and Model classes are unaware View classes (the ViewModel mustn’t assume types of rendering in the View  - e.g. that a button exists)
  • Model classes are unaware of ViewModel and View classes
  • ViewModel classes are aware of Model classes
  • View classes are aware of ViewModel classes

To summarise:

Aware of View Aware of Model Aware of ViewModel
View N/A No Yes
Model No N/A No
ViewModel No Yes N/A

Data binding facilitates loose coupling between the View and the ViewModel. It also supports a standardised input validation model.

The data is typically implemented as properties on the ViewModel. The View consumes that data via data binding. Application logic is typically implemented as methods on the ViewModel that the View can invoke through commanding.

A possible weakness with MVVM in Silverlight applications is the lack of support for Commands.

The following are the differences between Silverlight and WPF regarding commanding:

  • Routed commands are not available in Silverlight. However, the ICommand interface is available in Silverlight, allowing developers to create their own custom commands. The Composite Application Library provides the DelegateCommand and CompositeCommand classes to simplify command implementation. For more information, see the Commands technical concept.
  • In WPF, controls can be hooked up to commands through their Command property. By doing this, developers can declaratively associate controls and commands. This also means a control can interact with a command so that it can invoke the command and have its enabled status automatically updated. Silverlight controls do not currently support the Command property. To help work around this issue, the Composite Application Library provides an attached property-based extensibility mechanism that allows commands and controls to be declaratively associated with each other. For more information, see "Using Commands in Silverlight Commands" in the Commands technical concept.
  • There is no input gesture or input binding support in Silverlight.

http://msdn.microsoft.com/en-us/library/dd458872.aspx

ViewModel classes are easy to test, taking key logic out of the dreaded code behind files.

I need to check out a few things:

See also http://andysonlinenotes.blogspot.com/2010/06/stuff-i-should-be-interested-in.html

Saturday, 5 December 2009

?length=5 at the end of an ActionLink

I tried to add an action link to a view which would link to an action on a different controller but the links did not generate correctly and ended with ?length=5.

The following ActionLink was used on a view used by a job controller (JobController):

<%= Html.ActionLink("Edit", "Edit", "Query", new{ id = item.Id }) %>

This should have generated a link to the Edit action on the Query controller. However the links generated as follows:

http://<server here>/Job/Edit?Length=5

In other words they were still generated as if they were on the Job controller (I was using the standard {controller}/{action}/{id} type route).

The fix is to add null at the end of the call to ActionRoute:

<%= Html.ActionLink("Edit", "Edit", "Query", new{ id = item.Id }, null) %>

There are a stack of overrides of the ActionLink method and this forced ASP.Net MVC to use the right one.

Sunday, 22 November 2009

Using the HandleError attribute

You can conveniently handle exceptions in ASP.Net MVC using the [HandleError] attribute. However, there are a few things to bear in mind.

Update Web.config

You must add a customerrors section to Web.config. If you don’t do this nothing will happen.

<configuration>
    <system.web>
        <customErrors mode="On" />
    </system.web>
<configuration>

Beware of adding the attribute to the controller at class level

If you add the attribute to your controller class at the class level it can override any settings made on controller actions.

using System;
using System.Web.Mvc;
using Mail.Merge.Core.Domain;
using Mail.Merge.Core.Repository;
using Mail.Merge.Core.Repository.Specification;
using Mail.Merge.UI.MVC.Extensions;

namespace Mail.Merge.UI.MVC.Controllers
{
    [HandleError] // This will override any settings made on controller actions
    public class SalutationController : Controller
    {
        IRepository _repository;

        public SalutationController(IRepository repository)
        {
            _repository = repository;
        }

        // code snipped ...

        [AcceptVerbs(HttpVerbs.Post)]
        [HandleError(ExceptionType=typeof(SqlException),View="DeletionError")]
        public ActionResult Delete(int id, string button)
        {
            // code snipped ...
            return RedirectToAction("Index");
        }
    }
}

You can fix this behaviour though by modifying the [HandleError] attributes to use explicit ordering. For example in the code above set the attribute at the class level to be [HandleError(Order=0)]. Because the default order number is –1 this will force the controller action error handling filter to take precedence. 

InvalidDataAccessApiUsageException with Spring and NHibernate

If you get a Spring.Dao.InvalidDataAccessApiUsageException with the following message…

“Write operations are not allowed in read-only mode (FlushMode.NEVER) - turn your Session into FlushMode.AUTO or remove 'readOnly' marker from transaction definition”

…check that you have added the [Transaction(ReadOnly = false)] attribute to the appropriate data access method (assuming it’s a method that modifies data). Alternatively, if the attribute is already present, check that ReadOnly is not set to true.

Saturday, 21 November 2009

NullReferenceException if not using default binding

If you are not using the default binding mechanism in MVC and you are doing you own data validation (i.e. adding your own errors to the ModelState) the HtmlHelper class can throw a NullReferenceException. This occurs when there are validation errors.

System.NullReferenceException was unhandled by user code
  Message="Object reference not set to an instance of an object."
  Source="System.Web.Mvc"
  StackTrace:
       at System.Web.Mvc.HtmlHelper.GetModelStateValue(String key, Type destinationType)
       at System.Web.Mvc.Html.InputExtensions.InputHelper(HtmlHelper htmlHelper, InputType inputType, String name, Object value, Boolean useViewData, Boolean isChecked, Boolean setId, Boolean isExplicitValue, IDictionary`2 htmlAttributes)
       at System.Web.Mvc.Html.InputExtensions.TextBox(HtmlHelper htmlHelper, String name, Object value, IDictionary`2 htmlAttributes)
       at System.Web.Mvc.Html.InputExtensions.TextBox(HtmlHelper htmlHelper, String name, Object value)
       at ASP.views_salutation_edit_aspx.__RenderContent2(HtmlTextWriter __w, Control parameterContainer) in c:\source\MUI.MVC\Views\Salutation\Edit.aspx:line 25
       at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
       at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
       at System.Web.UI.Control.Render(HtmlTextWriter writer)
       at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
       at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
       at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
       at ASP.views_shared_site_master.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:\source\UI.MVC\Views\Shared\Site.Master:line 29
       at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
       at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
       at System.Web.UI.Control.Render(HtmlTextWriter writer)
       at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
       at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
       at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
       at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
       at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
       at System.Web.UI.Page.Render(HtmlTextWriter writer)
       at System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer)
       at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
       at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
       at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
       at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

The MVC Framework will try to find an AttemptedValue for every error it finds so you must add them or MVC will throw an exception.

AttemptedValues are automatically populated when you use default binding, if you call UpdateModel() or by passing the object to bind as a parameter. For example:

public ActionResult Create(MyClass myObject);

If you want to do it yourself you need to call ModelState.SetModelValue. For example:

ModelState.SetModelValue("Name", new ValueProviderResult(ValueProvider["Name"].AttemptedValue, salutation.Name, System.Globalization.CultureInfo.CurrentCulture));

Wednesday, 18 November 2009

Measuring query performance

To measure query performance you can use the SQL Profiler to log to a table then run the following queries.

Most frequent queries

SELECT
    DISTINCT
        CAST(textdata AS varchar(5000)) AS textdata,
        COUNT(duration) AS Occurences,
        AVG(duration) AS AvgDuration,
        SUM(duration) AS TotalDuration
FROM    [trace table name here]
WHERE   LoginName = 'login name here'
        AND textdata NOT LIKE '--%'
        AND CAST(textdata AS VARCHAR(5000)) <> 'exec sp_reset_connection'
GROUP BY CAST(textdata AS VARCHAR(5000))
ORDER BY COUNT(duration) DESC

Most inefficient queries

SELECT DISTINCT
        CAST(textdata AS VARCHAR(5000)) AS textdata,
        COUNT(duration) AS Occurences,
        AVG(duration) AS AvgDuration,
        SUM(duration) AS TotalDuration
FROM    [trace table name here]
WHERE   LoginName = 'login name here'
        AND textdata NOT LIKE '--%'
        AND CAST(textdata AS VARCHAR(5000)) <> 'exec sp_reset_connection'
GROUP BY CAST(textdata AS VARCHAR(5000))
ORDER BY AVG(duration) DESC

Monday, 16 November 2009

Commands in WPF

The GoF Command design pattern is defined as  "encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations". WPF Commands provide methods for decoupling UI events, the handling of these events and the registration of UI elements interested in handling the events.

WPF Commands are really very much like events but they offer some advantages:

  • Reuse – Commands can be registered with multiple controls allowing for reuse.
  • Routing – Commands based on the RoutedCommand base class can participate in event bubbling.
  • XAML integration – Commands can be defined and registered with controls in XAML.
  • Input gestures – There are a stack of build-in commands which are already configured to handle input gestures (e.g. using ApplicationCommands.Paste, a RoutedUICommand, will give you all Ctrl-V etc. out of the box).
  • Testability – Commands can be tested.
  • Localisation – Commands can be localised (which is done for you with built-in commands).

All WPF commands must implement a simple interface, ICommand:

public interface ICommand
{
    // Methods.
    void Execute(object parameter);
    bool CanExecute(object parameter);

    // Events.
    event EventHandler CanExecuteChanged;
}
  • Execute - contains the logic to perform the action that makes up the command
  • CanExecute - returns a value that determines if the command is currently valid
  • CanExecuteChanged event - raised when the value returned by the CanExecute method has changed

Built-in commands take advantage of CanExecute and CanExecuteChanged to enable/disable functionality for you (i.e. registered controls’ will automatically become enabled/disabled appropriately).

See http://www.microsoft.com/belux/msdn/nl/community/columns/jdruyts/wpf_commandpattern.mspx

See http://msdn.microsoft.com/en-us/library/ms752308.aspx

More to follow on this one…

Sunday, 15 November 2009

Dashboard output in CruiseControl.Net 1.5

This applies to CruiseControl.Net 1.5x which doesn’t show much in the way of output reports by default.
There are basically 2 types of output:
  1. Build report
  2. XSL report
These types of output are enabled by CruiseControl.Net plugins. The build report output appears in the build summary when you first view the build results in the dashboard. The XSL reports appear as menu items on the left when you are viewing build results.
Both types of report are enabled by XSL files that are located in the <web dashboard installation>\xsl folder. 
To modify the types of output you need to edit the dashboard.config file located in the web dashboard installation folder.
<?xml version="1.0" encoding="utf-8"?>
<dashboard>
  <remoteServices>
  ...
  </remoteServices>
  <plugins>
    <farmPlugins>
    ...
    </farmPlugins>
    <serverPlugins>
      ...
    </serverPlugins>
    <projectPlugins>
      <projectReportProjectPlugin />
      <viewProjectStatusPlugin />
      <latestBuildReportProjectPlugin />
      <viewAllBuildsProjectPlugin />
    </projectPlugins>
    <buildPlugins>
      <buildReportBuildPlugin>
        <xslFileNames>
          <xslFile>xsl\header.xsl</xslFile>
          <xslFile>xsl\modifications.xsl</xslFile>
          <xslFile>xsl\unittests.xsl</xslFile>
        </xslFileNames>
      </buildReportBuildPlugin>
      <buildLogBuildPlugin />
      <xslReportBuildPlugin xslFileName="xsl\AlternativeNUnitDetails.xsl" actionName="NUnitBuildReport" description="NUnit Report"></xslReportBuildPlugin>
      <xslReportBuildPlugin xslFileName="xsl\timing.xsl" actionName="NUnitTimingReport" description="NUnit Timing"></xslReportBuildPlugin>
      <xslReportBuildPlugin xslFileName="xsl\unittests.xsl" actionName="UnitTestsReport" description="Unit Tests"></xslReportBuildPlugin>
    </buildPlugins>
    <securityPlugins>
      <simpleSecurity />
    </securityPlugins>
  </plugins>
</dashboard>
The <buildreportbuildplugin> element contains a list of XSL files. The output generated by these files will appear in the build report.
The  <xslreportbuildplugin> elements contain one XSL file each. The output generated by these files will appear as individual XSL reports accessible via left-hand menu items in the build report.
Note: You will need to touch the dashboard web.config file to get the dashboard to read the modified dashboard.config file.

Tuesday, 10 November 2009

Generating insert statements

To generate insert statements from existing data create and run the following stored procedure (taken from http://vyaskn.tripod.com/code.htm).

SET NOCOUNT ON
GO

PRINT 'Using Master database'
USE master
GO

PRINT 'Checking for the existence of this procedure'
IF (SELECT OBJECT_ID('sp_generate_inserts','P')) IS NOT NULL --means, the procedure already exists
 BEGIN
  PRINT 'Procedure already exists. So, dropping it'
  DROP PROC sp_generate_inserts
 END
GO

--Turn system object marking on
EXEC master.dbo.sp_MS_upd_sysobj_category 1
GO

CREATE PROC sp_generate_inserts
(
 @table_name varchar(776),    -- The table/view for which the INSERT statements will be generated using the existing data
 @target_table varchar(776) = NULL,  -- Use this parameter to specify a different table name into which the data will be inserted
 @include_column_list bit = 1,  -- Use this parameter to include/ommit column list in the generated INSERT statement
 @from varchar(800) = NULL,   -- Use this parameter to filter the rows based on a filter condition (using WHERE)
 @include_timestamp bit = 0,   -- Specify 1 for this parameter, if you want to include the TIMESTAMP/ROWVERSION column's data in the INSERT statement
 @debug_mode bit = 0,   -- If @debug_mode is set to 1, the SQL statements constructed by this procedure will be printed for later examination
 @owner varchar(64) = NULL,  -- Use this parameter if you are not the owner of the table
 @ommit_images bit = 0,   -- Use this parameter to generate INSERT statements by omitting the 'image' columns
 @ommit_identity bit = 0,  -- Use this parameter to ommit the identity columns
 @top int = NULL,   -- Use this parameter to generate INSERT statements only for the TOP n rows
 @cols_to_include varchar(8000) = NULL, -- List of columns to be included in the INSERT statement
 @cols_to_exclude varchar(8000) = NULL, -- List of columns to be excluded from the INSERT statement
 @disable_constraints bit = 0,  -- When 1, disables foreign key constraints and enables them after the INSERT statements
 @ommit_computed_cols bit = 0  -- When 1, computed columns will not be included in the INSERT statement
 
)
AS
BEGIN

/***********************************************************************************************************
Procedure: sp_generate_inserts  (Build 22) 
  (Copyright © 2002 Narayana Vyas Kondreddi. All rights reserved.)
                                          
Purpose: To generate INSERT statements from existing data. 
  These INSERTS can be executed to regenerate the data at some other location.
  This procedure is also useful to create a database setup, where in you can 
  script your data along with your table definitions.

Written by: Narayana Vyas Kondreddi
         http://vyaskn.tripod.com

Acknowledgements:
  Divya Kalra -- For beta testing
  Mark Charsley -- For reporting a problem with scripting uniqueidentifier columns with NULL values
  Artur Zeygman -- For helping me simplify a bit of code for handling non-dbo owned tables
  Joris Laperre   -- For reporting a regression bug in handling text/ntext columns

Tested on:  SQL Server 7.0 and SQL Server 2000

Date created: January 17th 2001 21:52 GMT

Date modified: May 1st 2002 19:50 GMT

Email:   vyaskn@hotmail.com

NOTE:  This procedure may not work with tables with too many columns.
  Results can be unpredictable with huge text columns or SQL Server 2000's sql_variant data types
  Whenever possible, Use @include_column_list parameter to ommit column list in the INSERT statement, for better results
  IMPORTANT: This procedure is not tested with internation data (Extended characters or Unicode). If needed
  you might want to convert the datatypes of character variables in this procedure to their respective unicode counterparts
  like nchar and nvarchar
  

Example 1: To generate INSERT statements for table 'titles':
  
  EXEC sp_generate_inserts 'titles'

Example 2:  To ommit the column list in the INSERT statement: (Column list is included by default)
  IMPORTANT: If you have too many columns, you are advised to ommit column list, as shown below,
  to avoid erroneous results
  
  EXEC sp_generate_inserts 'titles', @include_column_list = 0

Example 3: To generate INSERT statements for 'titlesCopy' table from 'titles' table:

  EXEC sp_generate_inserts 'titles', 'titlesCopy'

Example 4: To generate INSERT statements for 'titles' table for only those titles 
  which contain the word 'Computer' in them:
  NOTE: Do not complicate the FROM or WHERE clause here. It's assumed that you are good with T-SQL if you are using this parameter

  EXEC sp_generate_inserts 'titles', @from = "from titles where title like '%Computer%'"

Example 5:  To specify that you want to include TIMESTAMP column's data as well in the INSERT statement:
  (By default TIMESTAMP column's data is not scripted)

  EXEC sp_generate_inserts 'titles', @include_timestamp = 1

Example 6: To print the debug information:
  
  EXEC sp_generate_inserts 'titles', @debug_mode = 1

Example 7:  If you are not the owner of the table, use @owner parameter to specify the owner name
  To use this option, you must have SELECT permissions on that table

  EXEC sp_generate_inserts Nickstable, @owner = 'Nick'

Example 8:  To generate INSERT statements for the rest of the columns excluding images
  When using this otion, DO NOT set @include_column_list parameter to 0.

  EXEC sp_generate_inserts imgtable, @ommit_images = 1

Example 9:  To generate INSERT statements excluding (ommiting) IDENTITY columns:
  (By default IDENTITY columns are included in the INSERT statement)

  EXEC sp_generate_inserts mytable, @ommit_identity = 1

Example 10:  To generate INSERT statements for the TOP 10 rows in the table:
  
  EXEC sp_generate_inserts mytable, @top = 10

Example 11:  To generate INSERT statements with only those columns you want:
  
  EXEC sp_generate_inserts titles, @cols_to_include = "'title','title_id','au_id'"

Example 12:  To generate INSERT statements by omitting certain columns:
  
  EXEC sp_generate_inserts titles, @cols_to_exclude = "'title','title_id','au_id'"

Example 13: To avoid checking the foreign key constraints while loading data with INSERT statements:
  
  EXEC sp_generate_inserts titles, @disable_constraints = 1

Example 14:  To exclude computed columns from the INSERT statement:
  EXEC sp_generate_inserts MyTable, @ommit_computed_cols = 1
***********************************************************************************************************/

SET NOCOUNT ON

--Making sure user only uses either @cols_to_include or @cols_to_exclude
IF ((@cols_to_include IS NOT NULL) AND (@cols_to_exclude IS NOT NULL))
 BEGIN
  RAISERROR('Use either @cols_to_include or @cols_to_exclude. Do not use both the parameters at once',16,1)
  RETURN -1 --Failure. Reason: Both @cols_to_include and @cols_to_exclude parameters are specified
 END

--Making sure the @cols_to_include and @cols_to_exclude parameters are receiving values in proper format
IF ((@cols_to_include IS NOT NULL) AND (PATINDEX('''%''',@cols_to_include) = 0))
 BEGIN
  RAISERROR('Invalid use of @cols_to_include property',16,1)
  PRINT 'Specify column names surrounded by single quotes and separated by commas'
  PRINT 'Eg: EXEC sp_generate_inserts titles, @cols_to_include = "''title_id'',''title''"'
  RETURN -1 --Failure. Reason: Invalid use of @cols_to_include property
 END

IF ((@cols_to_exclude IS NOT NULL) AND (PATINDEX('''%''',@cols_to_exclude) = 0))
 BEGIN
  RAISERROR('Invalid use of @cols_to_exclude property',16,1)
  PRINT 'Specify column names surrounded by single quotes and separated by commas'
  PRINT 'Eg: EXEC sp_generate_inserts titles, @cols_to_exclude = "''title_id'',''title''"'
  RETURN -1 --Failure. Reason: Invalid use of @cols_to_exclude property
 END


--Checking to see if the database name is specified along wih the table name
--Your database context should be local to the table for which you want to generate INSERT statements
--specifying the database name is not allowed
IF (PARSENAME(@table_name,3)) IS NOT NULL
 BEGIN
  RAISERROR('Do not specify the database name. Be in the required database and just specify the table name.',16,1)
  RETURN -1 --Failure. Reason: Database name is specified along with the table name, which is not allowed
 END

--Checking for the existence of 'user table' or 'view'
--This procedure is not written to work on system tables
--To script the data in system tables, just create a view on the system tables and script the view instead

IF @owner IS NULL
 BEGIN
  IF ((OBJECT_ID(@table_name,'U') IS NULL) AND (OBJECT_ID(@table_name,'V') IS NULL)) 
   BEGIN
    RAISERROR('User table or view not found.',16,1)
    PRINT 'You may see this error, if you are not the owner of this table or view. In that case use @owner parameter to specify the owner name.'
    PRINT 'Make sure you have SELECT permission on that table or view.'
    RETURN -1 --Failure. Reason: There is no user table or view with this name
   END
 END
ELSE
 BEGIN
  IF NOT EXISTS (SELECT 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = @table_name AND (TABLE_TYPE = 'BASE TABLE' OR TABLE_TYPE = 'VIEW') AND TABLE_SCHEMA = @owner)
   BEGIN
    RAISERROR('User table or view not found.',16,1)
    PRINT 'You may see this error, if you are not the owner of this table. In that case use @owner parameter to specify the owner name.'
    PRINT 'Make sure you have SELECT permission on that table or view.'
    RETURN -1 --Failure. Reason: There is no user table or view with this name  
   END
 END

--Variable declarations
DECLARE  @Column_ID int,   
  @Column_List varchar(8000), 
  @Column_Name varchar(128), 
  @Start_Insert varchar(786), 
  @Data_Type varchar(128), 
  @Actual_Values varchar(8000), --This is the string that will be finally executed to generate INSERT statements
  @IDN varchar(128)  --Will contain the IDENTITY column's name in the table

--Variable Initialization
SET @IDN = ''
SET @Column_ID = 0
SET @Column_Name = ''
SET @Column_List = ''
SET @Actual_Values = ''

IF @owner IS NULL 
 BEGIN
  SET @Start_Insert = 'INSERT INTO ' + '[' + RTRIM(COALESCE(@target_table,@table_name)) + ']' 
 END
ELSE
 BEGIN
  SET @Start_Insert = 'INSERT ' + '[' + LTRIM(RTRIM(@owner)) + '].' + '[' + RTRIM(COALESCE(@target_table,@table_name)) + ']'   
 END


--To get the first column's ID

SELECT @Column_ID = MIN(ORDINAL_POSITION)  
FROM INFORMATION_SCHEMA.COLUMNS (NOLOCK) 
WHERE  TABLE_NAME = @table_name AND
(@owner IS NULL OR TABLE_SCHEMA = @owner)



--Loop through all the columns of the table, to get the column names and their data types
WHILE @Column_ID IS NOT NULL
 BEGIN
  SELECT  @Column_Name = QUOTENAME(COLUMN_NAME), 
  @Data_Type = DATA_TYPE 
  FROM  INFORMATION_SCHEMA.COLUMNS (NOLOCK) 
  WHERE  ORDINAL_POSITION = @Column_ID AND 
  TABLE_NAME = @table_name AND
  (@owner IS NULL OR TABLE_SCHEMA = @owner)



  IF @cols_to_include IS NOT NULL --Selecting only user specified columns
  BEGIN
   IF CHARINDEX( '''' + SUBSTRING(@Column_Name,2,LEN(@Column_Name)-2) + '''',@cols_to_include) = 0 
   BEGIN
    GOTO SKIP_LOOP
   END
  END

  IF @cols_to_exclude IS NOT NULL --Selecting only user specified columns
  BEGIN
   IF CHARINDEX( '''' + SUBSTRING(@Column_Name,2,LEN(@Column_Name)-2) + '''',@cols_to_exclude) <> 0 
   BEGIN
    GOTO SKIP_LOOP
   END
  END

  --Making sure to output SET IDENTITY_INSERT ON/OFF in case the table has an IDENTITY column
  IF (SELECT COLUMNPROPERTY( OBJECT_ID(QUOTENAME(COALESCE(@owner,USER_NAME())) + '.' + @table_name),SUBSTRING(@Column_Name,2,LEN(@Column_Name) - 2),'IsIdentity')) = 1 
  BEGIN
   IF @ommit_identity = 0 --Determing whether to include or exclude the IDENTITY column
    SET @IDN = @Column_Name
   ELSE
    GOTO SKIP_LOOP   
  END
  
  --Making sure whether to output computed columns or not
  IF @ommit_computed_cols = 1
  BEGIN
   IF (SELECT COLUMNPROPERTY( OBJECT_ID(QUOTENAME(COALESCE(@owner,USER_NAME())) + '.' + @table_name),SUBSTRING(@Column_Name,2,LEN(@Column_Name) - 2),'IsComputed')) = 1 
   BEGIN
    GOTO SKIP_LOOP     
   END
  END
  
  --Tables with columns of IMAGE data type are not supported for obvious reasons
  IF(@Data_Type in ('image'))
   BEGIN
    IF (@ommit_images = 0)
     BEGIN
      RAISERROR('Tables with image columns are not supported.',16,1)
      PRINT 'Use @ommit_images = 1 parameter to generate INSERTs for the rest of the columns.'
      PRINT 'DO NOT ommit Column List in the INSERT statements. If you ommit column list using @include_column_list=0, the generated INSERTs will fail.'
      RETURN -1 --Failure. Reason: There is a column with image data type
     END
    ELSE
     BEGIN
     GOTO SKIP_LOOP
     END
   END

  --Determining the data type of the column and depending on the data type, the VALUES part of
  --the INSERT statement is generated. Care is taken to handle columns with NULL values. Also
  --making sure, not to lose any data from flot, real, money, smallmomey, datetime columns
  SET @Actual_Values = @Actual_Values  +
  CASE 
   WHEN @Data_Type IN ('char','varchar','nchar','nvarchar') 
    THEN 
     'COALESCE('''''''' + REPLACE(RTRIM(' + @Column_Name + '),'''''''','''''''''''')+'''''''',''NULL'')'
   WHEN @Data_Type IN ('datetime','smalldatetime') 
    THEN 
     'COALESCE('''''''' + RTRIM(CONVERT(char,' + @Column_Name + ',109))+'''''''',''NULL'')'
   WHEN @Data_Type IN ('uniqueidentifier') 
    THEN  
     'COALESCE('''''''' + REPLACE(CONVERT(char(255),RTRIM(' + @Column_Name + ')),'''''''','''''''''''')+'''''''',''NULL'')'
   WHEN @Data_Type IN ('text','ntext') 
    THEN  
     'COALESCE('''''''' + REPLACE(CONVERT(char(8000),' + @Column_Name + '),'''''''','''''''''''')+'''''''',''NULL'')'     
   WHEN @Data_Type IN ('binary','varbinary') 
    THEN  
     'COALESCE(RTRIM(CONVERT(char,' + 'CONVERT(int,' + @Column_Name + '))),''NULL'')'  
   WHEN @Data_Type IN ('timestamp','rowversion') 
    THEN  
     CASE 
      WHEN @include_timestamp = 0 
       THEN 
        '''DEFAULT''' 
       ELSE 
        'COALESCE(RTRIM(CONVERT(char,' + 'CONVERT(int,' + @Column_Name + '))),''NULL'')'  
     END
   WHEN @Data_Type IN ('float','real','money','smallmoney')
    THEN
     'COALESCE(LTRIM(RTRIM(' + 'CONVERT(char, ' +  @Column_Name  + ',2)' + ')),''NULL'')' 
   ELSE 
    'COALESCE(LTRIM(RTRIM(' + 'CONVERT(char, ' +  @Column_Name  + ')' + ')),''NULL'')' 
  END   + '+' +  ''',''' + ' + '
  
  --Generating the column list for the INSERT statement
  SET @Column_List = @Column_List +  @Column_Name + ',' 

  SKIP_LOOP: --The label used in GOTO

  SELECT  @Column_ID = MIN(ORDINAL_POSITION) 
  FROM  INFORMATION_SCHEMA.COLUMNS (NOLOCK) 
  WHERE  TABLE_NAME = @table_name AND 
  ORDINAL_POSITION > @Column_ID AND
  (@owner IS NULL OR TABLE_SCHEMA = @owner)


 --Loop ends here!
 END

--To get rid of the extra characters that got concatenated during the last run through the loop
SET @Column_List = LEFT(@Column_List,len(@Column_List) - 1)
SET @Actual_Values = LEFT(@Actual_Values,len(@Actual_Values) - 6)

IF LTRIM(@Column_List) = '' 
 BEGIN
  RAISERROR('No columns to select. There should at least be one column to generate the output',16,1)
  RETURN -1 --Failure. Reason: Looks like all the columns are ommitted using the @cols_to_exclude parameter
 END

--Forming the final string that will be executed, to output the INSERT statements
IF (@include_column_list <> 0)
 BEGIN
  SET @Actual_Values = 
   'SELECT ' +  
   CASE WHEN @top IS NULL OR @top < 0 THEN '' ELSE ' TOP ' + LTRIM(STR(@top)) + ' ' END + 
   '''' + RTRIM(@Start_Insert) + 
   ' ''+' + '''(' + RTRIM(@Column_List) +  '''+' + ''')''' + 
   ' +''VALUES(''+ ' +  @Actual_Values  + '+'')''' + ' ' + 
   COALESCE(@from,' FROM ' + CASE WHEN @owner IS NULL THEN '' ELSE '[' + LTRIM(RTRIM(@owner)) + '].' END + '[' + rtrim(@table_name) + ']' + '(NOLOCK)')
 END
ELSE IF (@include_column_list = 0)
 BEGIN
  SET @Actual_Values = 
   'SELECT ' + 
   CASE WHEN @top IS NULL OR @top < 0 THEN '' ELSE ' TOP ' + LTRIM(STR(@top)) + ' ' END + 
   '''' + RTRIM(@Start_Insert) + 
   ' '' +''VALUES(''+ ' +  @Actual_Values + '+'')''' + ' ' + 
   COALESCE(@from,' FROM ' + CASE WHEN @owner IS NULL THEN '' ELSE '[' + LTRIM(RTRIM(@owner)) + '].' END + '[' + rtrim(@table_name) + ']' + '(NOLOCK)')
 END 

--Determining whether to ouput any debug information
IF @debug_mode =1
 BEGIN
  PRINT '/*****START OF DEBUG INFORMATION*****'
  PRINT 'Beginning of the INSERT statement:'
  PRINT @Start_Insert
  PRINT ''
  PRINT 'The column list:'
  PRINT @Column_List
  PRINT ''
  PRINT 'The SELECT statement executed to generate the INSERTs'
  PRINT @Actual_Values
  PRINT ''
  PRINT '*****END OF DEBUG INFORMATION*****/'
  PRINT ''
 END
  
PRINT '--INSERTs generated by ''sp_generate_inserts'' stored procedure written by Vyas'
PRINT '--Build number: 22'
PRINT '--Problems/Suggestions? Contact Vyas @ vyaskn@hotmail.com'
PRINT '--http://vyaskn.tripod.com'
PRINT ''
PRINT 'SET NOCOUNT ON'
PRINT ''


--Determining whether to print IDENTITY_INSERT or not
IF (@IDN <> '')
 BEGIN
  PRINT 'SET IDENTITY_INSERT ' + QUOTENAME(COALESCE(@owner,USER_NAME())) + '.' + QUOTENAME(@table_name) + ' ON'
  PRINT 'GO'
  PRINT ''
 END


IF @disable_constraints = 1 AND (OBJECT_ID(QUOTENAME(COALESCE(@owner,USER_NAME())) + '.' + @table_name, 'U') IS NOT NULL)
 BEGIN
  IF @owner IS NULL
   BEGIN
    SELECT  'ALTER TABLE ' + QUOTENAME(COALESCE(@target_table, @table_name)) + ' NOCHECK CONSTRAINT ALL' AS '--Code to disable constraints temporarily'
   END
  ELSE
   BEGIN
    SELECT  'ALTER TABLE ' + QUOTENAME(@owner) + '.' + QUOTENAME(COALESCE(@target_table, @table_name)) + ' NOCHECK CONSTRAINT ALL' AS '--Code to disable constraints temporarily'
   END

  PRINT 'GO'
 END

PRINT ''
PRINT 'PRINT ''Inserting values into ' + '[' + RTRIM(COALESCE(@target_table,@table_name)) + ']' + ''''


--All the hard work pays off here!!! You'll get your INSERT statements, when the next line executes!
EXEC (@Actual_Values)

PRINT 'PRINT ''Done'''
PRINT ''


IF @disable_constraints = 1 AND (OBJECT_ID(QUOTENAME(COALESCE(@owner,USER_NAME())) + '.' + @table_name, 'U') IS NOT NULL)
 BEGIN
  IF @owner IS NULL
   BEGIN
    SELECT  'ALTER TABLE ' + QUOTENAME(COALESCE(@target_table, @table_name)) + ' CHECK CONSTRAINT ALL'  AS '--Code to enable the previously disabled constraints'
   END
  ELSE
   BEGIN
    SELECT  'ALTER TABLE ' + QUOTENAME(@owner) + '.' + QUOTENAME(COALESCE(@target_table, @table_name)) + ' CHECK CONSTRAINT ALL' AS '--Code to enable the previously disabled constraints'
   END

  PRINT 'GO'
 END

PRINT ''
IF (@IDN <> '')
 BEGIN
  PRINT 'SET IDENTITY_INSERT ' + QUOTENAME(COALESCE(@owner,USER_NAME())) + '.' + QUOTENAME(@table_name) + ' OFF'
  PRINT 'GO'
 END

PRINT 'SET NOCOUNT OFF'


SET NOCOUNT OFF
RETURN 0 --Success. We are done!
END

GO

PRINT 'Created the procedure'
GO


--Turn system object marking off
EXEC master.dbo.sp_MS_upd_sysobj_category 2
GO

PRINT 'Granting EXECUTE permission on sp_generate_inserts to all users'
GRANT EXEC ON sp_generate_inserts TO public

SET NOCOUNT OFF
GO

PRINT 'Done'

Sunday, 8 November 2009

Dependency Properties

Dependency properties are one of the features that allow for extension in WPF.

“Windows Presentation Foundation (WPF) provides a set of services that can be used to extend the functionality of a common language runtime (CLR) property. Collectively, these services are typically referred to as the WPF property system. A property that is backed by the WPF property system is known as a dependency property.”

See http://msdn.microsoft.com/en-us/library/ms752914.aspx

The value of a normal .NET property is read or written directly from or to a field in a class. The value of a DependencyProperty is read or written by calling GetValue() or SetValue() inherited from the DependencyObject base class.

Values are not stored in a field but in a dictionary provided by DependencyObject. The key is the name of the property and the value is the value you want to set.

The advantages of dependency properties include:

  • Change notification
    • Dependency properties have a built-in change notification mechanism so by registering a callback in the property metadata you get notified when the value of the property has been changed. Actions can be triggered in response to this notification like:
      • re-rendering appropriate elements,
      • updating the layout,
      • refreshing data-binding etc.
      • Look-up property triggers.
  • Property value inheritance
    • The value of a dependency property is resolved by using a value resolution strategy (i.e. flowing values down the element tree). But:
      • Not every dependency property participates in property value inheritance.
      • There may be other high-priority sources setting the property value.
  • Support for multiple providers
    • Property value providers can independently attempt to set the value of a dependency property. To avoid chaos there i a defined value resolution strategy.
  • Reduced memory footprint
    • The default values are stored once within the dependency property.

See http://wpftutorial.net/DependencyProperties.html

Friday, 6 November 2009

XAML markup extensions

“Markup extensions are a XAML concept. In attribute syntax, curly braces ({ and }) indicate a markup extension usage. This usage directs the XAML processing to escape from the general treatment of attribute values as either a literal string or a directly string-convertible value.” (my italics)

See http://msdn.microsoft.com/en-us/library/ms752059.aspx

“When used to provide an attribute value, the syntax that distinguishes a markup extension to a XAML processor is the presence of the opening and closing curly braces ({ and }). The type of markup extension is then identified by the string token immediately following the opening curly brace.

When used in property element syntax, a markup extension is visually the same as any other element used to provide a property element value: a XAML element declaration that references the markup extension class as an element, enclosed within angle brackets (<>). ”

See http://msdn.microsoft.com/en-us/library/ms747254.aspx

XAML-defined markup extensions

There are a number of XAML extensions not specific to WPF. These are usually identified by the prefix x: which is an XML prefix used to map the XAML namespace.

Extension tag Description
x:Type Supplies the Type object for the named type. This is used most frequently in styles and templates.
x:Static Produces static values from value-type code entities that are not directly the type of a property's value, but can be evaluated to that type.
x:Null Specifies null as a value for a XAML property.
x:Array Provides support for creation of general arrays in XAML syntax, for cases where the collection support provided by base elements and control models is deliberately not used.

Nested extension syntax

Extensions can be nested. For example:

<Setter Property="Background"  Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}" />

{} Escape Sequence / Markup Extension

To escape curly braces precede with the {} escape sequence, especially where the first character of the property is an opening curly brace. For example:

<Setter Property="SomeProperty"  Value="{}{" />

The value of SomeProperty will be set to {.

“The {} escape sequence is frequently required when specifying an XML type that must include a namespace qualifier in a location where XAML markup extension might appear. This includes the beginning of an XAML attribute value, and within a markup extension, immediately after an equal-sign. The following example shows escapes for an XML namespace that appears at the beginning of a XAML attribute value.”

  <StackPanel.Resources>
    <DataTemplate DataType="{}{http://planetsNS}Planet" >
      <StackPanel Orientation="Horizontal">
        <TextBlock Width="100" Text="{Binding Path=Element[{http://planetsNS}DiameterKM].Value}" />
        <TextBlock Width="100" Text="{Binding Path=Attribute[Name].Value}" />
        <TextBlock Text="{Binding Path=Element[{http://planetsNS}Details].Value}" /> 
      </StackPanel>
    </DataTemplate>
  </StackPanel.Resources>

See http://msdn.microsoft.com/en-us/library/ms744986.aspx

Thursday, 5 November 2009

Fulltext catalogues

To identify the full text catalogues run the following SQL:
SELECT name 
FROM sys.fulltext_catalogs;
GO
Alternatively use the SQL Management Studio.
  • Go to Object Explorer and connect to your server.
  • Expand the Databases node and find the database in question.
  • Expand the Storage > Full Text Catalogues node.
  • Right-click on a catalogue name and select Properties.
Note that the Tables/Views page of the Full-Text Catalog Properties dialog box shows how the catalogue tracks changes (radio buttons at the bottom of the screen).

Common tasks

Rebuild
“Tells SQL Server to rebuild the entire catalog. When a catalog is rebuilt, the existing catalog is deleted and a new catalog is created in its place. All the tables that have full-text indexing references are associated with the new catalog. Rebuilding resets the full-text metadata in the database system tables.”
Reorganize
“Tells SQL Server to perform a master merge, which involves merging the smaller indexes created in the process of indexing into one large index. Merging the full-text index fragments can improve performance and free up disk and memory resources. If there are frequent changes to the full-text catalog, use this command periodically to reorganize the full-text catalog.
REORGANIZE also optimizes internal index and catalog structures.
Keep in mind that, depending on the amount of indexed data, a master merge may take some time to complete. Master merging a large amount of data can create a long running transaction, delaying truncation of the transaction log during checkpoint. In this case, the transaction log might grow significantly under the full recovery model. As a best practice, ensure that your transaction log contains sufficient space for a long-running transaction before reorganizing a large full-text index in a database that uses the full recovery model. For more information, see Managing the Size of the Transaction Log File.”

SQL command to run

You can trigger a rebuild or reorganisation using the following command:
ALTER FULLTEXT CATALOG catalog_name 
{ REBUILD [ WITH ACCENT_SENSITIVITY = { ON | OFF } ]
| REORGANIZE
| AS DEFAULT 
}
See http://msdn.microsoft.com/en-us/library/ms176095.aspx

Tuesday, 3 November 2009

Assembly resource URI format

I can never remember the URI format for resources embedded in assemblies.  So:

assembly://<assemblyname>/<namespace>/<resource>

The <namespace> part can include folder names separated from the base assembly namespace by dots (.). For example a Spring configuration file located in a SpringConfig folder for an application with a default namespace of Mail.Merge.Console would have a resource definition of:

assembly://Mail.Merge.Console/Mail.Merge.Console.SpringConfig/SpringDataAccess.xml

Wednesday, 28 October 2009

SOLID principles

The term SOLID is an acronym for:
  • Single Responsibility Principle
    • A class should have one, and only one, reason to change.
    • If a class assumes more than one responsibility, then there will be more than one reason for it to
      change.
    • If a class has more then one responsibility, then the responsibilities become coupled.
  • Open-Closed Principle
    • Software entities should be open for extension but closed for modification.
    • You should be able to extend a classes behaviour, without modifying it.
    • The primary mechanisms behind the Open-Closed principle are abstraction (inheritance) and polymorphism.
  • Liskov Substitution Principle
    • Derived classes must be substitutable for their base classes.
    • Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it.
    • A.K.A. Design By Contract.
    • Derived types are completely substitutable for their base types.
  • Interface Segregation Principle
    • Make fine grained interfaces that are client specific.*
    • Clients should not be forced to depend upon interfaces that they do not use.
  • Dependency Inversion Principle
    • Depend on abstractions, not on concretions.
    • Modules that encapsulate high level policy should not depend upon
      modules that implement details.
    • High level modules should not depend upon low level modules. Both should depend upon abstractions.
    • Abstractions should not depend upon details. Details should depend upon abstractions.

* “This principle deals with the disadvantages of “fat” interfaces. Classes that have “fat” interfaces are classes whose interfaces are not cohesive. In other words, the interfaces of the class can be broken up into groups of member functions. Each group serves a different set of clients. Thus some clients use one group of member functions, and other clients use the other groups.”
See http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

Tuesday, 27 October 2009

Naming unit tests

In his book The Art of Unit Testing, Roy Osherove suggests the following format for the name of unit tests:

MethodUnderTest_Scenario_Behaviour()

  • MethodUnderTest - The name of the method being tested.
  • Scenario - This part gives us the “with” part of the name: “When I call method X with a null value, then it should do Y.”
  • Behaviour - This part specifies in plain English what the method should do or return, or how it should behave, based on the current scenario: “When I call method X with a null value, then it should do Y.”

Thursday, 22 October 2009

Expression Trees

In LINQ, expression trees represent structured queries that target sources of data that implement IQueryable<T>. Expression trees are also used in LINQ to represent lambda expressions that are assigned to variables of type Expression<TDelegate>.
Instances of Expression<TDelegate> can be executed. To execute an expression tree call the Compile method to create an executable delegate and then call invoke it. Executing an expression tree may return a value, or it may just perform an action such as calling a method.
We can use the Expression Trees to create data store agnostic dynamic query APIs.
The foundation of the Expression Trees in .Net is the System.Linq.Expression namespace. The MSDN documentation states:
“Expression trees represent language-level code in the form of data. The data is stored in a tree-shaped structure. Each node in the expression tree represents an expression, for example a method call or a binary operation such as x < y.”
See http://msdn.microsoft.com/en-us/library/bb397951.aspx
Expression nodes are encapsulated by instances of the Expression class and its subclasses. To build expression tree nodes you use static factory methods on the Expression classes.
You can also get the compiler to build an expression tree for you from a lambda expression. When you do this the Expression is always of type Expression<TDelegate>. The Expression<TDelegate> type provides the Compile method, that compiles the code represented by the expression tree into an executable delegate.
Expression trees are immutable so if you want to modify an expression tree, you must create a copy with the necessary modifications. You can use an expression tree visitor to traverse the existing expression tree. See http://msdn.microsoft.com/en-us/library/bb882521.aspx for an example on how to do this.
Note:
“Only those expression trees that represent functions, namely Expression<TDelegate> and its parent type LambdaExpression, can be compiled into executable code. To execute other types of expression trees, you must first wrap them in a LambdaExpression node. You can obtain such a LambdaExpression by calling the Lambda method and passing the expression tree as the argument.”

Dynamic Queries

For basic information on creating dynamic queries see http://msdn.microsoft.com/en-us/library/bb882637.aspx.
For an example of using AND/OR operations see http://msdn.microsoft.com/en-us/library/bb546136.aspx.

Tuesday, 20 October 2009

IQueryable and IQueryable<T>

The type returned from a LINQ query will be of type IQueryable. For example, the var in the following query will be an IQueryable:
var query = from u in data.Users 
            where u.LastName == "Smith" 
            select new { u.FirstName, u.LastName}
IQueryable has very few members and has 3 properties of particular interest:
public interface IQueryable : IEnumerable
{
    Type ElementType { get; }
    Expression Expression { get; }
    IQueryProvider Provider { get; }
}
An IQueryable has an Expression property. In other words we can get hold of the Expression Tree for the query (note that the Expression type is the base class for the open generic implementations such as Expression<T>). If we can get hold of the Expression Tree we can manipulate it!
Because IQueryable has a GetEnumerator() method you can enumerate the results of the query. 
See http://msdn.microsoft.com/en-us/library/system.linq.iqueryable.aspx
IQueryable<T> implements IQueryable (which itself implements IEnumerable) and “provides functionality to evaluate queries against a specific data source wherein the type of the data is known”. The MSDN documentation states:
“This interface inherits the IEnumerable<T> interface so that if it represents a query, the results of that query can be enumerated. Enumeration forces the expression tree associated with an IQueryable<T> object to be executed. Queries that do not return enumerable results are executed when the Execute<TResult>(Expression) method is called.
The definition of "executing an expression tree" is specific to a query provider. For example, it may involve translating the expression tree to a query language appropriate for an underlying data source.
The IQueryable<T> interface enables queries to be polymorphic. That is, because a query against an IQueryable data source is represented as an expression tree, it can be executed against different types of data sources.” (my italics)
IQueryable<T> has a stack of members including all the query type operations you would expect in the form of extension methods (e.g.  Distinct, Max, Min, etc). It has the same properties as IQueryable, including the Expression property.
See http://msdn.microsoft.com/en-us/library/bb337580.aspx

Monday, 19 October 2009

Expression<TDelegate> Class

Documentation is here: http://msdn.microsoft.com/en-us/library/bb335710.aspx
The documentation states:
Represents a strongly typed lambda expression as a data structure in the form of an expression tree. This class cannot be inherited…
“…When a lambda expression is assigned to a variable, field, or parameter whose type is Expression<TDelegate>, the compiler emits instructions to build an expression tree…
…The expression tree is an in-memory data representation of the lambda expression. The expression tree makes the structure of the lambda expression transparent and explicit. You can interact with the data in the expression tree just as you can with any other data structure.
The ability to treat expressions as data structures enables APIs to receive user code in a format that can be inspected, transformed, and processed in a custom manner. For example, the LINQ to SQL data access implementation uses this facility to translate expression trees to Transact-SQL statements that can be evaluated by the database.”

Properties

Expression<TDelegate> has 4 properties:
  • Body – gets the body of the lambda expression.
  • NodeType – gets the node type of the expression (an enumeration of 45 different values representing all the different types of expression such as constants, greater than (>), less than (<) etc).
  • Parameters – gets the parameters of the lambda expression.
  • Type - gets the static type of the expression that this Expression represents (i.e. one of the Func types such as Func<T1, T2, TResult>).

Methods

There is really only one interesting method on Expression<TDelegate>:
  • Compile - compiles the lambda expression described by the expression tree into executable code.

Namespace

Expression<TDelegate> is part of the System.Linq.Expressions namespace which contains a number of interesting classes:
Class Description
BinaryExpression Represents an expression that has a binary operator.
ConditionalExpression Represents an expression that has a conditional operator.
ConstantExpression Represents an expression that has a constant value.
ElementInit Represents an initializer for a single element of an IEnumerable collection.
Expression Provides the base class from which the classes that represent expression tree nodes are derived. It also contains static (Shared in Visual Basic) factory methods to create the various node types. This is an abstract class.
Expression<TDelegate> Represents a strongly typed lambda expression as a data structure in the form of an expression tree. This class cannot be inherited.
InvocationExpression Represents an expression that applies a delegate or lambda expression to a list of argument expressions.
LambdaExpression Describes a lambda expression.
ListInitExpression Represents a constructor call that has a collection initializer.
MemberAssignment Represents initializing a field or property of a newly created object.
MemberBinding Provides the base class from which the classes that represent bindings that are used to initialize members of a newly created object derive.
MemberExpression Represents accessing a field or property.
MemberInitExpression Represents calling a constructor and initializing one or more members of the new object.
MemberListBinding Represents initializing the elements of a collection member of a newly created object.
MemberMemberBinding Represents initializing members of a member of a newly created object.
MethodCallExpression Represents calling a method.
NewArrayExpression Represents creating a new array and possibly initializing the elements of the new array.
NewExpression Represents a constructor call.
ParameterExpression Represents a named parameter expression.
TypeBinaryExpression Represents an operation between an expression and a type.
UnaryExpression Represents an expression that has a unary operator.
See http://msdn.microsoft.com/en-us/library/system.linq.expressions.aspx.
More to follow on some of these separate types.

ExpressionTreeVisulaizer in VS 2008

To install the ExpressionTreeVisualizer:
  1. Get the C# language samples that include example LINQ projects from http://code.msdn.microsoft.com/csharpsamples.
  2. Open and build the ExpressionTreeVisualizer solution.
  3. Copy the generated ExpressionTreeVisualizer.dll file into ..\Program Files\Microsoft Visual Studio 9.0\Common7\Packages\Debugger\Visualizers directory.
If and when you set a breakpoint and hover over an Expression you can click on the magnifying glass icon in the pop-up tooltip to access the Expression Visualizer.

Friday, 16 October 2009

Func and Action

Func(TResult) is a delegate type that encapsulates a method that has no parameters and returns a value of the type specified by the TResult parameter.
MSDN documentation states:
“You can use this delegate to represent a method that can be passed as a parameter without explicitly declaring a custom delegate. The method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have no parameters and must return a value.”
The documentation goes on to point out that if you need a delegate type that does not have a return type use Action instead.
There are 4 further delegate types related to Func(TResult):
  • Func(T, TResult)
  • Func(T1, T2, TResult)
  • Func(T1, T2, T3, TResult)
  • Func(T1, T2, T3, T4, TResult)
Each of these encapsulates a method that takes one or more parameters of various types and which returns TResult.
There are equivalent Action types for encapsulating delegates that do not have a return type.
This is all very interesting when you consider you can assign a lambda expression to a Func, e.g.
Func<int, int, int> function = (a,b) => a + b;
…and that you can also create an Expression from a lambda represented as a Func.
Expression<Func<int, int, int>> expression = (a,b) => a + b;
More to follow on Expression.
Friday, 16 October 2009,

A reminder about delegates

A delegate is a reference type used to encapsulate a method with a specific signature and return type. You can encapsulate any matching method in that delegate.

From MSDN documentation:

“A delegate is a type that references a method. Once a delegate is assigned a method, it behaves exactly like that method. The delegate method can be used like any other method, with parameters and a return value…

…Any method that matches the delegate's signature, which consists of the return type and parameters, can be assigned to the delegate. This makes is possible to programmatically change method calls, and also plug new code into existing classes. As long as you know the delegate's signature, you can assign your own delegated method.

This ability to refer to a method as a parameter makes delegates ideal for defining callback methods.”

The documentation goes on to state that delegates have the following properties (and others):

  • Delegates are similar to C++ function pointers, but are type safe.
  • Delegates allow methods to be passed as parameters.
  • Delegates can be used to define callback methods.
  • Delegates can be chained together; for example, multiple methods can be called on a single event.

Delegate creation syntax:

// define the delegate
public delegate void MyDelegate(object sender, EventArgs e);

// The public member variable myDelegate is an instance of a MyDelegate delegate
public MyDelegate myDelegate;

// assign method SomeMethod to myDelegate
myDelegate = SomeMethod(object myObject, new EventArgs());

Note that this removes any previously assigned methods from the delegate and assigns the new one. You can use an alternative syntax to add more than one method to a delegate. You can then execute all methods in one delegate call:

public delegate  void MyDelegate(object sender, EventArgs e);
public MyDelegate myDelegate;
 
myDelegate += SomeMethod(object myObject, new EventArgs()); 
myDelegate += SomeOtherMethod(object myObject, new EventArgs());
 
//Call both methods
myDelegate(obj, args);

Events

The event keyword restricts how delegates are used. Events are delegates that:

  • Can only be registered with += and not with the assignment operator (=)
  • Can only be called by methods of the class that defines the event
public delegate  void MyDelegate(object sender, EventArgs e);
public event MyDelegate myDelegate;
 
myDelegate += SomeMethod(object myObject, new EventArgs()); 
myDelegate += SomeOtherMethod(object myObject, new EventArgs());

// Compilation error here! Can't asign to an event.
myDelegate = YetAnotherMethod(object myObject, new EventArgs());
 
//Call both methods
myDelegate(obj, args);

Tuesday, 13 October 2009

SQL Server versioning

SQL Server versions are:

Version Number
SQL Server version
2007.100.1600.0
SQL Server 2008 RTM
2007.100.2531.0
SQL Server 2008 Service Pack 1
2005.90.1399
SQL Server 2005 RTM
2005.90.2047
SQL Server 2005 Service Pack 1
2005.90.3042
SQL Server 2005 Service Pack 2
2005.90.4035
SQL Server 2005 Service Pack 3
2000.80.194.0
SQL Server 2000 RTM
2000.80.384.0
SQL Server 2000 SP1
2000.80.534.0
SQL Server 2000 SP2
2000.80.760.0
SQL Server 2000 SP3
2000.80.760.0
SQL Server 2000 SP3a
2000.8.00.2039
SQL Server 2000 SP4

See http://support.microsoft.com/kb/321185

To find the version of SQL Server try running the following SQL query:

SELECT SERVERPROPERTY('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition')

Sunday, 11 October 2009

Why LINQ to SQL sucks

Given the following repository interface how can you create a LINQ to SQL implementation that uses data transfer objects (POCO classes that are agnostic as to the underlying data access technology) when instantiating the repository?
public interface IRepository<T> where T : class 
{ 
    void Save(T instance); 

    void Delete(T instance); 

    TResult FindOne<TResult>(ISpecification<T, TResult> specification); 

    IQueryable<TResult> FindAll<TResult>(ISpecification<T, TResult> specification); 

    IQueryable<T> FindAll(); 
}
Your LINQ to SQL repository implementation might look something like this (I’ve snipped a bunch of code and left one method implemented):
public class Repository<T> : IRepository<T> where T : class 
{ 
    private readonly DataContext _ctx; 

    public Repository(DataContext ctx) 
    { 
        _ctx = ctx; 
    } 

    public void Save(T instance) ... 
    public void Delete(T instance) ...  
    public TResult FindOne<TResult>(ISpecification<T, TResult> specification) ... 
    public IQueryable<TResult> FindAll<TResult>(ISpecification<T, TResult> specification) ...

    public IQueryable<T> FindAll() 
    { 
        return _ctx.GetTable<T>().AsQueryable(); 
    } 
}
The problem is that the call to _ctx.GetTable<T>() expects T to be a type defined in the LINQ to SQL layer – not a data transfer type. 
Let’s say you have a User data transfer class. You would expect to instantiate the repository as follows:
var repository = new Repository<User>();
This won’t work because the User type would have to be the User type defined in the LINQ to SQL layer. Your client code will no longer be agnostic as to the data access layer.
How rubbish is that!
There are some very hacky workarounds that all involve writing lots of unnecessary code.
See:
Sunday, 11 October 2009

Friday, 9 October 2009

Queuing theory

Little’s law

In a stable system the average amount of time it takes to get something through a process is equal to the number of things in the process divided by the average completion rate.

Cycle Time = (Things in Process)/(Average Completion Rate)

To reduce cycle time either:

  1. Get things done faster (usually involves spending money)
  2. Reduce the number of things in process

Reducing Cycle Time

Queuing theory offers some more suggestions on reducing cycle time:

  1. Even out the arrival of work
  2. Minimise the number of things in process
  3. Minimise the size of things in process
  4. Establish a regular cadence
  5. Limit work capacity
  6. Use pull scheduling

On evening out the arrival of work

“Queues at the beginning of the development process may seem like a good place to hold work so that it can be released to the development organisation at an even pace. But those queues should be no bigger than necessary to even out the arrival of work…”

On minimising the number of things in process

“…Queues of work waiting for approval absorb energy every time they are estimated, reprioritised, and discussed at meetings. To-do queues often serve as buffers that insulate developers from customers; they can be abused to obscure reality and they often generate unrealistic expectations.”

On limiting work to capacity

“Time sometimes seems to be elastic in a development organisation. People can and do work overtime, and when this happens in short bursts they can even accomplish more this way. However, sustained overtime is not sustainable. People get tired and careless at the end of a long day, and more often than not, working long hours will slow things down rather than speed things up.”

Avoid the thrashing that occurs when there is too much work for the number of people available.

Some final thoughts

Some general rules when using queues:

  1. Queues must be kept short – perhaps two cycles of work.
  2. Managers can reorganise or change items at any time that they are in a queue. But once teams start to work on an item, they should not interfere.
  3. Teams pull work from a queue at a regular cadence until that work is done. It is the pull system that keeps the team busy at all times while limiting work to capacity.
  4. Queues should not be used to mislead people into thinking that their requests are going to be dealt with if the team does not have the capacity to respond.

See Implementing Lean Software Development: From Concept to Cash.

Thursday, 8 October 2009

Data file sizes in SQL Server 2005

If you want to list all the data and log files plus their sizes try the following SQL:

USE master ; 
GO 

SELECT  db.dbid AS 'DB ID', 
        db.name AS 'Database Name', 
        af.name AS 'Logical Name', 
        af.[size] as 'File Size (in 8-kilobyte (KB) pages)', 
        (((CAST(af.[size] AS DECIMAL(18, 4)) * 8192) / 1024) / 1024) AS 'File Size (MB)', 
        ((((CAST(af.[size] AS DECIMAL(18, 4)) * 8192) / 1024) / 1024) 
          / 1024 ) AS 'File Size (GB)', 
        af.filename AS 'Physical Name' 
FROM    sys.sysdatabases db 
        INNER JOIN sys.sysaltfiles af ON db.dbid = af.dbid 
WHERE   [fileid] IN (1, 2);

Wednesday, 7 October 2009

The IQueryable<T> interface

The MSDN documentation states that it:

“Provides functionality to evaluate queries against a specific data source wherein the type of the data is known…

The IQueryable<(Of <(T>)>) interface is intended for implementation by query providers.

This interface inherits the IEnumerable<(Of <(T>)>) interface so that if it represents a query, the results of that query can be enumerated. Enumeration forces the expression tree associated with an IQueryable<(Of <(T>)>) object to be executed. Queries that do not return enumerable results are executed when the Execute<(Of <(TResult>)>)(Expression) method is called.

The definition of "executing an expression tree" is specific to a query provider. For example, it may involve translating the expression tree to a query language appropriate for an underlying data source.

The IQueryable<(Of <(T>)>) interface enables queries to be polymorphic. That is, because a query against an IQueryable data source is represented as an expression tree, it can be executed against different types of data sources.”

IQueryable<T> appears to be an excellent choice as a return type for repository methods. Because it is the enumeration that forces the execution of the expression tree the actual database query is deferred until that point. By passing IQueryable<T> around we can add to the query at any point and only execute it when the result is enumerated.

However, there is a down side. If we return an IQueryable<T> we are not really returning the data but rather a query that can be used to get the data. This is not what repositories are intended to do – the repository should execute the query and return the data, not return queries which can be used to get the data at some indeterminate point.

I think the jury is still out on this one.

Tuesday, 6 October 2009

Adding time to dates in SQL Server

To add time to a date use the DATEADD Transact-SQL statement.

DATEADD (datepart , number, date )

The date parts can be:

datepart Abbreviations

year

yy, yyyy

quarter

qq, q

month

mm, m

dayofyear

dy, y

day

dd, d

week

wk, ww

weekday

dw, w

hour

hh

minute

mi, n

second

ss, s

millisecond

ms

microsecond

mcs

nanosecond

ns

For example:

SELECT DATEADD(dd, 12, "29 March 1964")

To get the date at midnight you can use the following:

SELECT DATEADD(dd,0, DATEDIFF(dd,0, GETDATE())) as date_at_midnight

See http://msdn.microsoft.com/en-us/library/ms186819.aspx for details.

Gallio test automation platform

Gallio is a neutral test automation platform designed to help run tests from a variety of testing frameworks in a unified environment. It is a project that seems to be a spin off from the MbUnit team but will run tests from a variety of other frameworks including NUnit.

The Gallio Icarus test runner is somewhat similar to the test runner you get with Resharper. There is also a command line tool called Echo that has support for generating test reports etc.

Gallio also integrates with CruiseControl.Net. You need to setup your build to export a report in Gallio XML format (e.g. run Gallio.Echo.exe as a build task) and update the <publishers> node in ccnet.config. There is then a new report plug-in to be added to the CCNet dashboard to display the Gallio reports.

http://www.gallio.org/

Sunday, 4 October 2009

NHibernate and quoted identifiers

If you have a column or table name that is a reserved word or which contains spaces etc. you can force NHibernate to use quoted identifiers by using a back tick in the table/column name:

<class name="LineItem" table="`Line Item`">
    <id name="Id" column="`Item Id`"/><generator class="assigned"/></id>
    <property name="ItemNumber" column="`Item #`"/>
    ...
</class>

Friday, 2 October 2009

Querying the results of a stored procedure

If you want to run a query against the results of a stored procedure a simple solution is to use a temporary table and the “INSERT INTO” SQL syntax. For example:

CREATE TABLE #MyTempTable (
     some_field varchar(10),
     some_other_field varchar(40)
)

INTERT INTO #MyTempTable
     EXEC my_stored_procedure

SELECT * FROM #MyTempTable WHERE some_field LIKE '%some value%'
    
DROP TABLE #MyTempTable
GO

Lean development – eliminate waste

One of the principles of lean software development is to eliminate waste. Anything that not adding value to the customer is a candidate to be considered as waste.

In terms of software development wasteful activities can include:

  • Writing unnecessary code and features
  • Delays in the development process
  • Unclear or ambiguous requirements
  • Unnecessary bureaucracy (this could include estimating)

Other candidates for waste are:

  • Implementing features not actually used by the customer
  • Waiting (e.g. for another team to complete something)
  • Bugs and low quality software

There are 3 terms that are often applied to waste in a system:

  • Muda – an activity that is wasteful or unproductive
  • Mura – unevenness or inconsistency
  • Muri - overburden

Mary Poppendiek states the following:

“The first step in lean thinking is to understand what value is and what activities and resources are absolutely necessary to create that value. Once this is understood, everything else is waste.”

http://www.poppendieck.com/papers/LeanThinking.pdf

And this:

“All lean thinking starts with a re-examination of what waste is and an aggressive campaign to eliminate it. Quite simply, anything you do that does not add value from the customer perspective is waste. The seven wastes of software development are:

  • Partially Done Work (the “inventory” of a development process
  • Extra Processes (easy to find in documentation-centric development)
  • Extra Features (develop only what customers want right now)
  • Task Switching (everyone should do one thing at a time)
  • Waiting (for instructions, for information)
  • Handoffs (tons of tacit knowledge gets lost)
  • Defects (at least defects that are not quickly caught by a test)”

http://www.poppendieck.com/pdfs/Lean_Software_Development.pdf

Wednesday, 30 September 2009

Thursday, 24 September 2009

Using idref when configuring objects

Using the idref element is "an error-proof way" to pass the id of one object to another in Spring.Net configuration files. Using idref is preferable because the IoC will validate that referenced objects exist at deployment time rather than waiting for objects to actually be instantiated.

So, this...

<object id="theTargetObject" type="..."> 
. . . 
</object> 

<object id="theClientObject" type="..."> 
  <property name="targetName"> 
    <idref object="theTargetObject"/> 
  </property> 
</object>

is prefereable to this...

<object id="theTargetObject" type="...">
. . .
</object>
 
<object id="theClientObject" type="...">
  <property name="targetName" value="theTargetObject"/>
</object>

See the Spring.Net documentation (section 5.3.2.1.1).

Constructor vs setter injection

Choosing between constructor or setter injection is not straight forwards and in practice can lead to difficult choices. In cases where objects have a large number of required dependencies this issue really raises its head.

Spring.Net's documentatioon states:
"The Spring team generally advocates the usage of setter injection, since a large number of constructor arguments can get unwieldy, especially when some properties are optional. The presence of setter properties also makes objects of that class amenable to reconfigured or reinjection later. Managment through WMI is a compelling use case.

Some purists favor constructor-based injection. Supplying all object dependencies means that the object is always returned to client (calling) code in a totally initialized state. The disadvantage is that the object becomes less amenable to reconfiguration and re-injection...

...Since you can mix both, Constructor- and Setter-based DI, it is a good rule of thumb to use constructor arguments for mandatory dependencies and setters for optional dependencies."
Martin Fowler also has a few words of advice on this issue:
"The choice between setter and constructor injection is interesting as it mirrors a more general issue with object-oriented programming - should you fill fields in a constructor or with setters.

My long running default with objects is as much as possible, to create valid objects at construction time.... Constructors with parameters give you a clear statement of what it means to create a valid object in an obvious place. If there's more than one way to do it, create multiple constructors that show the different combinations...

...But with any situation there are exceptions. If you have a lot of constructor parameters things can look messy, particularly in languages without keyword parameters. It's true that a long constructor is often a sign of an over-busy object that should be split, but there are cases when that's what you need...

...If you have multiple constructors and inheritance, then things can get particularly awkward. In order to initialize everything you have to provide constructors to forward to each superclass constructor, while also adding you own arguments. This can lead to an even bigger explosion of constructors.

Despite the disadvantages my preference is to start with constructor injection, but be ready to switch to setter injection as soon as the problems I've outlined above start to become a problem." - http://martinfowler.com/articles/injection.html#ConstructorVersusSetterInjection
The Spring.Net documentation goes on to point out that with constructor injection it is possible to get into a situation where you have unresolvable circular dependencies. These situations are detected by Spring.Net which throws an ObjectCurrentlyInCreationException. Spring offer some helpfull advice:
"One possible solution to this issue is to edit the source code of some of your classes to be configured via setters instead of via constructors. Alternatively, avoid constructor injection and stick to setter injection only. In other words, although it is not recommended, you can configure circular dependencies with setter injection."
In short the choice between setter and constructor is not clear and you need to make your own choice based on circumstances. This ambiguity is arguably a weakness with Dependency Injection.