Unable to update the EntitySet - because it has a DefiningQuery and no element exists in the element to support the current operation.

Error:
Unable to update the EntitySet 'Classroom' because it has a DefiningQuery and no <InsertFunction> element exists in the <ModificationFunctionMapping> element to support the current operation.

This error is raised while using Entity Framework.
While trying to save and persist db changes it raise this error. This error happens only in particular save and not every other places. The save operation raising this error is most probably an insert or a delete operation; like or example in my case:

db.Classrooms.Add(classroom);
db.SaveChanges();

Cause:
Eventhought the error message is a bit cryptic, the cause of the issue is simpler. The reason for this error is because the Primary key for the table is not set.

Solution:
Set the Primary key for the table and update the Entity Model (edmx file). This should clear the "Unable to update the EntitySet - because it has a DefiningQuery and no element exists in the element to support the current operation." exception.

LINQ : How to check if a record exists in the database

Issue: How to check if a record exists in the database using LINQ

// Solution 1: Select . Don't use SingleOrDefault because if there are more than one record returned it throws exception.
var res = (from cls in db.Classrooms
                 where cls.Name == "10A"
                 select cls).SingleOrDefault();
                
if(res != null)
{
    //record exists
}

// Solution 2: Select Count if you don't want to load the entity. This is an efficient method but not the most efficient. The LINQ expression translates to Count(*) in SQL.
int res = (from cls in db.Classrooms
                 where cls.Name == "10A"
                 select cls).count();
                
if(res > 0)
{
    //record exists
}

// Solution 3:
Classroom cls = db.Classrooms.FirstOrDefault(cls => cls.Name == "10A");
if(cls != null) {
    // record exists
}
else {
    // record does not exist
}

// Solution 4: This is the most effective solution
// If you only want to know if such a Record exists:
// This is the most efficient as it generates an IF EXISTS SQL query
return db.Classrooms.Any(cls => cls.Name == "10A"); // true if exists
// Similar expression is:
return db.Classrooms.Where(cls => cls.Name == "10A").Any();

// Solution 5:
// If you want a count of how many such Record exists:
return db.Classrooms.Count(cls => cls.Name == "10A");

// Solution 6:
// If you want an enumeration (IEnumerable<Record>) of all such Record:
return db.Classrooms.Where(cls => cls.Name == "10A");

Open URL in Browser Programatically -IE/FF/Chrome [Windows Forms]

Problem:
I want to open a URL in desktop web browser programatically.
I want to open it in different browsers of my choice.

Solution:
Here are some code blocks to open a url in the browsers of our choice.

Below code will open a specific url in your default browser configured:
System.Diagnostics.Process.Start("http://www.habeeb.in");

To open the url in Internet Explorer, use the code:
System.Diagnostics.Process.Start("iexplore.exe", "http://www.habeeb.in");

To open the url in firefox, use the code:
System.Diagnostics.Process.Start("firefox.exe", "http://www.habeeb.in");

To open the url in Chrome, use the code:
System.Diagnostics.Process.Start("chrome.exe", "http://www.habeeb.in");







These solutions are based on Windows Desktops Winforms Applications.

"Add Web Reference" missing in Visual Studio 2010/2012 - Solution

Issue:
Where is the Add Web Reference option in Visual Studio 2010 and 2012.

Did microsoft remove the option to add web service and retained option only to use WCF references (Service Reference) ?

Everytime Microsoft comes up with a new version of a product, some of the options are either renamed or rearranged.

The same happened with Visual Studio 2010.
The option to add web reference is still available but is misplaced.

Solution:
To access the option follow the steps below:

1) Right Click the Project -> Select "Add Service Reference". You get the "Add Service Reference" window.
2) On its left bottom there is an "Advanced..." button. It will take you to the "Service Reference Settings" window.
3) Bottom left of this window there is the old "Add Web Reference..." button dumped in a corner.
Click to get the "Add Web Reference window".

Screenshots:

 

How to declare local variable in ASP.NET MVC Razor?

Issue:
How to declare local variable in ASP.NET MVC Razor?
This is a very common scenario that newbies in ASP.NET MVC Razor view comes across.
It would be confusing when even with the "@" sign before the declaration it doesn't work.

Solution:
The solution as simple as placing the whole declation statement inside curly braces.
Even multiple declarations can be placed inside a curly braces block.
The declaration and usage would be as below.

@{int count = 1;}
@foreach (var step in level.steps)
{
    <div>
        <span class="title">@step.Name</span>
        <span class="meaning">@step.Description</span>
    </div>
}

How to add text to beginning or end of each line using notepad++

Get your text to modify in notepad++.

Step 1) Bring up the Find/Replace Dialog box by going to menu Search->Replace; or using shortcut CTRL+H.
Step 2) Select the "Regular expression" option in the "Search Mode" section of the dialog box.
Step 3) Enter "^" into the "Find what" textbox. ("^" denotes (matches) beginning of a line in Regular Expression syntax)
Step 4) In this example we will add "http://" to the beginning of each line. So enter "http://" (without double quotes) in the "Replace with" textbox.
Step 5) Press "Replace All" and your text will have "http://" at the beginning of each line.

Similar steps can be followed to add texts to the end of each line. Just use "$" instead of "^". In Regular Expression syntax, "$" matches the end of a line.

ASP.NET 4.0 A potentially dangerous Request.Form value was detected from the client.

Issue:
"A potentially dangerous Request.Form value was detected from the client".


Cause:
This error happens in ASP.NET when you try to submit text to server which contain HTML Tags. This is a mechanism in ASP.NET environment to safagaurd from cross sire scripting attack.


Solution:
The error can be suppressed by setting a property to your page directive. The property and its value is as follows:
validateRequest="false" .
So the part of the Page Directive will look like below:
<pages validateRequest="false" />

But with .NET Framework 4.0 and above, the error started showing up again even with the validateRequest property set to "false".
To overcome this error in .NET Framework 4.0 you will need one more step.
You will need to set the "requestValidationMode" property  to "2.0" to the httpRuntime configuration section of the web.config file. The resulting tag will look like:
<httpRuntime requestValidationMode="2.0"/>

If your web.config file does not have a httpRuntime section already, then add it inside the
<system.web> section.

If you want to turn off request validation for users globally, the following line in the web.config file within <system.web> section will help:
<pages validateRequest="false" />