Nullable int (int?) problem in entity framework

Question

4.20/5 (2 votes)

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Hi,

Let me explain my question in a simple example.

I have a table named "Person" in mssql.
I am using entity framework 5.0

Person
Id Name Number
1 Tom 5
2 Mary NULL
3 Henry 8

"Number" field is a nullable field.

When I run the code below, it finds the person "Mary" as I want and shows us "Person with Null Number exists!";

C#

using (Entities entities = new Entities())
{
	if (entities.Person.Where(p => p.Number == null).Any())
	{
		MessageBox.Show("Person with Null Number exists!");
	}
	else
	{
		MessageBox.Show("Person with Null Number doesn't exist!");
	}
}

but when I change code to below, it doesnot work same, it returns false and shows us "Person with Null Number doesn't exist!"

C#

int? nullValue = null;

using (Entities entities = new Entities())
{
	if (entities.Person.Where(p => p.Number == nullValue).Any())
	{
		MessageBox.Show("Person with Null Number exists!");
	}
	else
	{
		MessageBox.Show("Person with Null Number doesn't exist!");
	}
}

What is the diffence between them?
Could you help me about this?

Thanks in advance

Posted 17-Jun-14 23:00pm

ubudak

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Comments

Herman<T>.Instance 18-Jun-14 5:38am

the diff? NULL vs nullValue!
What is nullValue for kind of object?

ubudak 18-Jun-14 6:04am

"nullValue" is just the name of the variable.
As you can see in the example, type of it is "Nullable int" (int?)

http://msdn.microsoft.com/en-us/library/ms366789(v=vs.110).aspx

2 solutions

Solution 2

There must be a bug in linq-to-entities for version 5.0. I have tested it with version 6.1 and I didn't observe such thing.

here is the code:

C#

class Program
    {
        static void Main(string[] args)
        {
            int? i1 = null;

            using (TESTEntities ctx = new TESTEntities())
            {
                ctx.Database.Log = Console.Write;
                var exists = ctx.TABLE_A.Where(e1 => e1.A_NUM == null).Any();

                if(exists)
                    Console.WriteLine("exists"); // prints
                else
                    Console.WriteLine("not exists");

                Console.ReadKey();
            }

            using (TESTEntities ctx = new TESTEntities())
            {
                ctx.Database.Log = Console.Write;
                var exists = ctx.TABLE_A.Where(e1 => e1.A_NUM == i1).Any();

                if (exists)
                    Console.WriteLine("exists"); // prints
                else
                    Console.WriteLine("not exists");

                Console.ReadKey();
            }

            Console.ReadKey();
        }
    }

and the output:

Opened connection at 18/06/2014 12:59:32 PM +03:00
SELECT
    CASE WHEN ( EXISTS (SELECT
        1 AS [C1]
        FROM [dbo].[TABLE_A] AS [Extent1]
        WHERE [Extent1].[A_NUM] IS NULL
    )) THEN cast(1 as bit) WHEN ( NOT EXISTS (SELECT
        1 AS [C1]
        FROM [dbo].[TABLE_A] AS [Extent2]
        WHERE [Extent2].[A_NUM] IS NULL
    )) THEN cast(0 as bit) END AS [C1]
    FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]
-- Executing at 18/06/2014 12:59:33 PM +03:00
-- Completed in 16 ms with result: SqlDataReader

Closed connection at 18/06/2014 12:59:33 PM +03:00
exists
Opened connection at 18/06/2014 1:00:37 PM +03:00
SELECT
    CASE WHEN ( EXISTS (SELECT
        1 AS [C1]
        FROM [dbo].[TABLE_A] AS [Extent1]
        WHERE ([Extent1].[A_NUM] = @p__linq__0) OR (([Extent1].[A_NUM] IS NULL)
AND (@p__linq__0 IS NULL))
    )) THEN cast(1 as bit) WHEN ( NOT EXISTS (SELECT
        1 AS [C1]
        FROM [dbo].[TABLE_A] AS [Extent2]
        WHERE ([Extent2].[A_NUM] = @p__linq__0) OR (([Extent2].[A_NUM] IS NULL)
AND (@p__linq__0 IS NULL))
    )) THEN cast(0 as bit) END AS [C1]
    FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]
-- p__linq__0: 'null' (Type = Int32)
-- Executing at 18/06/2014 1:00:37 PM +03:00
-- Completed in 9 ms with result: SqlDataReader

Closed connection at 18/06/2014 1:00:37 PM +03:00
exists

you can either use sql profiler or context.Database.Log to see the actual query. it will show what happens.

Posted 18-Jun-14 0:08am

Vedat Ozan Oner

Updated 18-Jun-14 0:13am

v2

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ubudak · Accepted Answer · 2014-06-18T00:18:00

Solution 3

as mention the article below, setting "ObjectContextOptions.UseCSharpNullComparisonBehavior Property" to true is enough for solution

http://www.seventy-3.com/entity-framework-and-null-variables/

Posted 18-Jun-14 0:18am

ubudak

Comments

Vedat Ozan Oner 18-Jun-14 6:23am

ok, then it is not a bug, but I count it as hidden bug because default behavior must be 'true' since it is easy to fall into pit as we see in your case.

ubudak 18-Jun-14 6:28am

i think it was set to true as default in ef 6.
thank you very much for your comments and answers :)