How to get IS NULL in expression (To get null values from database)

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Hi,
I am using entity framework in my application. Consider I am having a following table structure

SQL

Employee(
ID uniqueidentifier,
Name varchar(100) not null,
JobId uniqueidentifier null)

I am using the following expression to get the data

C#

Expression<Func<Employee,true>> predicate=p=>p.JobId==JobIdVariable;
**JobIdVariable is nullable Guid.

So I am using the above expression in Where Clause of Employee object Context.Above solution works fine if jobIdVariable has any data but when it is NULL, then the query returns no rows. When I use SQL profiler, I am getting the following where clause
JobId = NULL, but in this case I have to get JobId IS NULL. So how can I modify my expression to get the Null values from DB.

Thanks for your time

Posted 17-Nov-14 21:24pm

Prasaad SJ

Updated 17-Nov-14 21:32pm

Shweta N Mishra

v2

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2 solutions

Solution 1

replace the NULL with 0 in both side of where condition.

something like

SQL

Isnull(JobID,0)=Isnull(jobIdVariable,0).

You would have to convert above expression as per the language requirement.

Posted 17-Nov-14 21:35pm

Shweta N Mishra

Updated 17-Nov-14 21:36pm

v2

Comments

Prasaad SJ 18-Nov-14 3:44am

Hi Shweta,
Can you describe this in detail? What is Isnull here? I am using C# btw.

Shweta N Mishra 18-Nov-14 3:51am

Isnull is a function in SQL which replaces Null value to given value, in above example it will replace it to zero. In C# you can use string.IsNullOrEmpty to get same result.

Prasaad SJ 18-Nov-14 4:52am

Hi Shweta,
I m sorry, I still couldn't get your solution. string.IsNullorEmpty always return a bool and can we use this in expression to compare?? And more over my data type is GUID? (so I can't use .ToString here, it will throw error when the value is null).

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Prasaad SJ · Accepted Answer · 2014-11-22T15:40:00

After few trial attempts, I could find the solution for this question. If the type is of nullable type, then in expression we have use both Equals and == .

Eg: In my above case in the question, its working correct when

C#

Expression<func><employee,true>> predicate;
if(JobIdVariable==null)
{
    predicate=p=>p.JobId.Equals(null);
   //In this case, the value has to be null and compare has to be Equals else it through some Object related error.
}
else
{
    predicate=p=>p.JobId==JobIdVariable;
//Here, it has to be == comparision else some runtime error is thrown.
}</func>