I Learnt Today…

2009-05-11

I have being working on a software application made on .Net and recently my client asked me to use D LINQ instead of SQL.

D LINQ has great benefits loaded! As I started working with DLINQ I started to know that preventing SQL injection is not a headache anymore and misspelled SQL queries will not trouble agian at run time because DLINQ generates all necessary SQL inside the framework!

I chose to use annotations inside the class instead of using separate xml file. Following is a part of the first class I ported to D LINQ.

</p>

<table(Name:="tbl_Process")> _
Public Class Process
<column(Name:="ProcessID", DbType:="Int", isprimarykey:=True)> _
Public ProcessID As Integer
<column(Name:="BusinessProcessID", DbType:="varchar(50)")> _
Public BusinessProcessID As String
<column(Name:="ProcessText", DbType:="varchar(50)", isprimarykey:=True)> _
Public ProcessText As String
...
...

ProcessID column is the primary key of my database table tbl_Process.

Important Point: I use database to auto-generate values for the primary key column (integer value incremented by one).

So when I run the application, It gave me this unexpected error:

Cannot insert explicit value for identity column in table ‘tbl_Process’ when IDENTITY_INSERT is set to OFF.

Basically, the IDENTITY_INSERT when using the database to auto generate value for a field but when I ran a SQL insert statement at the database end it worked fine!

After some tough time I found out the solution for this problem!

When we use an auto-generate field in a data table we have to specifically mention it in the matching field in the appropriate class.

The code to state this is:

Syntax:

IsDbGenerated:=True

This has to be added to the annotation added for the specific column like:

</p>

<column(Name:="ProcessID", DbType:="Int", isprimarykey:=True, IsDbGenerated:=True)> _
Public ProcessID As Integer

Now D LINQ can understand that the field value is auto-generated by the database!

Was this post helpful to you? How can I improve? – Your comment is highly appreciated!

Cassian Menol Razeek

2008-12-26

Today I was experimenting on a grid view where I was trying to select multiple rows of the grid view using a check box column.

I wrote some code in the CheckedChanged of checkbox but then I found that the code was not executed when the state of the checkbox is changed.

So I did a little googling and found out about this AutoPostBack property. This property defines whether the control should post back to the server each time when the user interacts with the control. Or, according to this scenario, a post back will fire when the user clicks on the check box or when the Checked property is changed.

AutoPostBack :

This value holds a boolean value (true/false)

If the property is set to true, a post back is sent immediately to the server and no post back is occurred when set to false.

The Use of AutoPostBack:

According to MSDN, for most WebControls, when AutoPostBack is false, only the events from actions that cause a net change in the state of the control are submitted to the server.

In other words some events are not queued to the server. For example no event is fired when a user selects a value from a drop down list or when user presses Enter or Tab key after entering a value to a textbox.

If you want such events to be fired then you have to enable autopostback by setting autopostback property to true.

How AutoPostBack Works :

When AutoPostBack is enabled, the .Net framework automatically injects following additional items into the generated HTML code.

1. Two Hidden variables with name __EVENTTARGET and __EVENTARGUMENT
2. A Java script method with name __doPostBack (eventtarget, eventargument)
3. OnChange JavaScript event to the control

What is __EVENTTARGET :

__EVENTTARGET tells the server which control wants to fire the event so that the framework can fire the event on that control.

What is __EVENTARGUMENT :

__EVENTARGUMENT can be used to provide additional information to the server about the event.

What is __doPostBack (eventtarget, eventargument) :

Parameters sent to this method holds relevant target and event argument values and this method sets those values into __EVENTTARGET and __EVENTARGUMENT hidden variables so that the server can read those.

Then this method submits the form to the server where the appropriate event will be fired.

What is OnChange JavaScript event to the control :

Every control has a client side event called OnChange. When AutoPostBack is enabled for a control the framework sets the handler for this client side event as the __doPostBack method and will pass the name of the control as the first parameter, eventtarget.

Ex/

Following shows how the framework binds the __doPostBack method to the OnChange event.

<input type=”checkbox” onclick=“javascript:setTimeout(‘__doPostBack(\’CheckBox1\’,\’\')‘, 0)” />

Was this post helpful to you? How can I improve? – Your comment is highly appreciated!

Cassian Menol Razeek

Recommended Books:

• Pro ASP.NET 3.5 in C# 2008

• Professional ASP.NET 2.0 Special Edition
• Beginning ASP.NET 3.5: In C# and VB Languages

2008-12-22

Sometimes things we consider as simple take much time to be accomplished than we expect just because we forget!

Today I wanted to save a copy of a web based visual studio 2005 solution but it took life 10 minutes for me to accomplish that because I had completely forgotten the method to do it. Since keeping track of what I learn is one objective of this blog I decided to include this small detail today.

How to save a copy a solution in visual studio 2005 (Save As)

Select the solution (click on it) in the solution explorer

Now go to File menu and there will be a command to Save the solution to any place you want.

Ex/

If your solution name is “My Solution.sln”

When you select your solution in the solution explorer and go to the file menu, you will see command like:

Save My Solution.sln As

Simply click on that and you will get the usual Save As dialog box.

Some Details

Even though you can select the place to save project files in web based solutions such as web sites, the solution is saved in a different location which is located in your My Documents folder.

The solution file contains information about your projects and files including paths so if you want to move the entire solution to a different computer to continue work on a different workstation then this tip will become handy unless you don’t forget things as I do

Was this post helpful to you? How can I improve? – Your comment is highly appreciated!

Cassian Menol Razeek

Recommended Books:

• Microsoft – Visual Studio 2005 Unleashed
• Microsoft – Visual Studio 2008 Unleashed