Cannot add an entity with a key that is already in use, LINQ

When you have table with ID coulumn (uniqueidentifier) and default value = (newid()),
than the above error occur.

To Resolve:

1) go to your .DBML file design view
2) go to property of particular columns
3) set "Auto generated Value" = true.

it will add following in DBML file IsDbGenerated="true"

Power shell, installutil

Error occur while installing powershell dll.

System.Reflection.ReflectionTypeLoadException: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information

Resolution:
make sure you have all the project reference dll in the project, developer always forgot reference dll while delpoying the project.

alternate approch is to load the reference DLL into GAC

String or Binary Data Would Be Truncated Error, LINQ

Error: String or Binary Data Would Be Truncated.

Desc:
Generally this error occurs when we are trying to inser/update large value in SQL server table that are not fit into columns lenght of table.

In one scenario i experienced the following scenario:

I had the one enum like below:
public enum MyEnum
{ First = 101, Second=102, Sixth=103)

now I was using this enum like MyEnum.First and assigning to the one variable
But when i was trying to insert that entity in database using LINQ i was getting the above error:


After doing debugging, I've to do following changes

var myvar = (int) MyEnum.First;

The above statement will return the 101,

that's it for now.

object reference not set to an instance of an object C#

Error: object reference not set to an instance of an object

C# developer usually getting the above error, I'd suggeste first check where you are using Trim(), Substring(), Length(), ToUpper(), ToLower() function with string variables in your codind.

To Resolve:
if(!String.IsNullOrEmpty(userFirstName))
{

-- your userFirstName assignment code here
}