Entity Framework Error: Resource not found for segment 'Property'

I was getting "Resource not found for segment 'Property'" error with the below code. I am loading some data from the database using .Net Entity Framework.


 private void LoadItem(int specId)
 {
       var query = DataContext.Items.Where( x => x.SpecId == specID );

       DataServiceQuery dsq = DataServiceQuery)query;

       dsq.BeginExecute(  ar =>
       {
             this.items = dsq.EndExecute( ar ).SingleOrDefault();
       },
       null );
       }
 }

The above code threw an exception when the data query returned no records. I was expecting SingleOrDefault() to return default value (which is NULL) if no matching records were found. But, instead I was getting "Resource not found for segment 'Property'" exception.

After doing some investigation I found out that the exception was due to the fact that I was using primary key field in my data service query.

       var query = DataContext.Items.Where( x => x.SpecId == specID );

Here the field SpecId was a primary key. In Entity Framework if your data service query is performed on a primary key, then SingleOrDefault() and FirstOrDefault() methods will throw an exception if no matching records were found.

To resolve this issue, I set the following property to TRUE on the data service DataContext. This line will suppress the "Resource Not Found" exception.

DataConext.IgnoreResourceNotFoundException = true;

SQL: Deleting duplicate records from table

Here is one way to delete duplicate records from a table:

Consider we have some duplicate records in TempTable which has a unique identifier column called "RowId".

delete from TempTable
where RowId not in
(
select min(ROWID)
from TempTable
group by column1, column2,...
)

For each duplicate set of duplicate records, the above query retains one row with minimum RowId and deletes all other duplicate records. If you want to retain row with maximum RowId and delete all other duplicate records, then just replace the min() method with max().

SQL Error: None of the result expressions in a CASE specification can be NULL

I got this error when my CASE statement in SQL returned NULL and did not have any ELSE section in the CASE statement: "None of the result expressions in a CASE specification can be NULL"

The CASE statement which resulted in error was like this:

SELECT 

CASE WHEN StudentId = 0 THEN null END

I wanted to return NULL when StudentId = 0; else return the StudentId.

The above query did not work without the ELSE part. After adding the ELSE section like below the query executed without error:

SELECT 

CASE WHEN StudentId = 0 THEN null ELSE StudentId END

Creating DataGridTemplateColumn from code behind

We can create DataGridTemplateColumn from code behind by defining a DataTemplate in the ResourceDictionary xaml and then use the DataTemplate to create the DataGridTemplateColumn.

In the below sample code, I am creating a data grid column with checkbox.

In the ResourceDictionary xaml, add DataTemplate for the checkbox:


<DataTemplate x:Key="CheckboxTemplate">
<CheckBox IsChecked="{Binding IsSelected, Mode=TwoWay}" />
</DataTemplate>

From the code behind create the DataGridTemplateColumn for the checkbox:


DataGridTemplateColumn checkboxColumn = new DataGridTemplateColumn()
{
      CellTemplate = App.Current.Resources["CheckboxTemplate"] as DataTemplate
};

Double click issue with DataGridCheckbox column

DataGridCheckboxColumn in DataGrid seems to have double click issue. One has to click twice to check or uncheck, first click to select the row and the second click for the checkbox. We can use DataGridTemplateColumn instead for the checkbox which does not have double click issue. 

sample code:

<DataGridTemplateColumn Header="Name">

<controlsData:DataGridTemplateColumn.CellTemplate>

<DataTemplate>

<CheckBox Content="{Binding Name}" IsChecked="{Binding Path=IsSelected,Mode=TwoWay}" />

</DataTemplate>

</controlsData:DataGridTemplateColumn.CellTemplat>

</DataGridTemplateColumn>

IIS version on Windows versions

Every Windows version has it's own IIS version. Here are some Windows versions:

Windows Server 2000 - IIS version 5.0
Windows XP Professional - IIS version 5.1
Windows Server 2003 - IIS version 6.0
Windows Vista - IIS version 7.0
Windows Server 2008 - IIS version 7.0

Using WebGet and WebInvoke

nice article on WebGet and WebInvoke attributes: Using WebGet and WebInvoke

LINQ to Entities does not support Contains() method

We are using .NET Entity Framework in our project and today I wrote a LINQ to Entities query to fetch records from table A if corresponding records are not found in table B. Let us take example of customer orders scenario. I want to get all the customers who don't have a order in the Orders table. What I needed was "NOT IN" or "NOT EXISTS" SQL equivalent in LINQ to Entities. I knew that we have Contains() method in LINQ to SQL which is equivalent to NOT EXISTS in SQL. So, I tried following LINQ to Entities query to return all the costumers who don't have a order in the Orders table:

from c in context.Customers
where !( from o in context.Orders select o.CustomerId ).Contains( c.CustomerId )
select c

I was confident this would work, but no the above query did not work!!. I got an error that LINQ to Entities does not support Contains() method. It is frustrating to know that the same Contains() method works in LINQ to SQL but not in LINQ to Entities. Why not support such basic functionality.

I had other frustrating moments with LINQ to Entities too. I prefer to just use LINQ to SQL and stay away from LINQ to Entities.

The NOT EXISTS equivalent in LINQ to SQL

Here is a sample LINQ to SQL query to return all the customers who don't have an order in the Orders table:

var query =
from c in Customers
where !( from o in Orders select o.CustomerId ).Contains( c.CustomerId )
select c;

Useful Keyboard Shortcuts for Microsoft Visual Studio

Here are some useful keyboard shortcuts for Microsoft Visual Studio:

F5 => Build
CTRL+F5 => Execute
F9 => Breakpoint for debugging
F10 => Single step during debugging
F11 => Get into function or method during debugging

CTRL+K+K => Book Mark
CTRL+K+N => Go to next book mark
CTRL+K+P => Go to previous book mark

CTRL-C => Copy
CTRL-V => Paste
CTRL-X => Cut
CTRL-A => Select All
CTRL-Z => Undo
ALT-TAB => Switch between open programs
CTRL-TAB => Switch between windows in the current program
CTRL-END => Go to the end of the document
CTRL-HOME => Go to the start of the document
END => Go to the end of the line
HOME => Go to the start of the line
SHIFT-END => Select from the current cursor position to the end of the line
SHIFT-HOME => Select from the current cursor position to the start of the line

F4 => Repeat the last action (only works in most Microsoft Office
applications, such as Excel/Visio/ Word, but very powerful in those)

CTRL-SHIFT-RightArrow => Select from the current cursor position to the end of the current word (including space)

CTRL-SHIFT-LeftArrow => Select from the current cursor position to the start of the prior word

CTRL-F => Find (open the Find dialog in many applications)

CTRL-H => Find and Replace (open the Find and Replace dialog in many
applications)

CTRL-SHIFT-UpArrow => Select from the current cursor position to the start of the current line of next line up

CTRL-SHIFT-DownArrow => Select from the current cursor position to the end of the current or next line down

CTRL-G => Go to a specific line number (works in notepad, Visual Studio,
other editing programs)

Firebug for Firefox

Firebug integrates with Firefox to put a wealth of web development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.

Download Firebug from here: http://getfirebug.com/

Internet Explorer Developer Toolbar

The Microsoft Internet Explorer Developer Toolbar provides a variety of tools for quickly creating, understanding, and troubleshooting Web pages.

Download the IE Developer Toolbar here: http://www.microsoft.com/downloads/en/details.aspx?FamilyID=95e06cbe-4940-4218-b75d-b8856fced535

Silverlight error: The debugger cannot continue running the process.

Today I got this error while debugging my silverlight application and the debugger just crashed without any useful error information. I got this error when the debugger crashed:

"The debugger cannot continue running the process. Process was terminated."

After doing some debugging and research I found this thread online where in many people had the same issue because of recursive call in class property:

http://social.msdn.microsoft.com/Forums/en-US/vsdebug/thread/f9b08dd4-8d20-4104-9a24-9f002caceb48/

I looked at my code and indeed I had a recursive call in one of my property by mistake.

private bool isUser;
public bool IsUser
{
get { return IsUser; }
set
{
IsUser = value;
OnPropertyChanged( "IsUser" );
}
}

As you can see in the above code my getter was recursively referring to IsUser property itself instead of the field isUser. This was just coding error but it took some time to figure out the root cause as the debugger was crashing without proper error information.