How can i query for null values in entity framework?

Question

I want to execute a query like this

   var result = from entry in table
                     where entry.something == null
                     select entry;

and get an IS NULL generated.

Edited: After the first two answers i feel the need to clarify that I'm using Entity Framework and not Linq to SQL. The object.Equals() method does not seem to work in EF.

Edit no.2: The above query works as intended. It correctly generates IS NULL. My production code however was

var value = null;
var result = from entry in table
                         where entry.something == value
                         select entry;

and the generated SQL was something = @p; @p = NULL. It seems that EF correctly translates the constant expression but if a variable is involved it treats it just like a normal comparison. Makes sense actually. I'll close this question

Answer 1

var result = from entry in table
             where entry.something.Equals(null)
             select entry;

MSDN Reference: LINQ to SQL: .NET Language-Integrated Query for Relational Data

Answer 2

to deal with Null Comparisons use Object.Equals() instead of ==

check this reference

Answer 3

If it is a nullable type, maybe try use the HasValue property?

var result = from entry in table
                 where !entry.something.HasValue
                 select entry;

Don't have any EF to test on here though... just a suggestion =)

Answer 4

It appears that Linq2Sql has this "problem" as well. It appears that there is a valid reason for this behavior due to whether ANSI NULLs are ON or OFF but it boggles the mind why a straight "== null" will in fact work as you'd expect.

Answer 5

var result = from entry in table
                     where entry.something == null
                     select entry;

The above query works as intended. It correctly generates IS NULL. My production code however was

var value = null;
var result = from entry in table
                         where entry.something == value
                         select entry;

and the generated SQL was something = @p; @p = NULL. It seems that EF correctly translates the constant expression but if a variable is involved it treats it just like a normal comparison. Makes sense actually.

Answer 6

Workaround for Linq-to-SQL:

var result = from entry in table
             where entry.something.Equals(value)
             select entry;

Workaround for Linq-to-Entities (ouch!):

var result = from entry in table
             where (value == null ? entry.something == null : entry.something == value)
             select entry;

This is a nasty bug which has bitten me several times. If this bug has affected you too, please visit the bug report on Microsoft Connect and let Microsoft know that this bug has affected you as well.

[Edit]: It seems that the Entity Framework team has... deleted almost all of the EF bug reports from Microsoft Connect!?!? I've recreated this one..