Linq to SQL nullable int？

Question

I have the following linq query (pretty simple):

var jobs = from j in db.jobmsts
    join jd in db.jobdtls on j.jobdtl_id equals jd.jobdtl_id
    where j.jobmst_type != 1 && j.jobmst_prntid.Equals(folder.FolderID)
    orderby j.jobmst_name
    select new
        {
            JobID = j.jobmst_id,
            JobName = j.jobmst_name,
            Description = j.jobmst_desc,
            Source = jd.Source
        };

folder.FolderID is a nullable int (int?) that is passed into the method as a parameter. So, when it's null, the query returns no results. But if I execute the same query in TSQL:

select * from jobmst j 
join jobdtl jd on j.jobdtl_id = jd.jobdtl_id 
where j.jobmst_type != 1 and j.jobmst_prntid is null

I get 6 records. Oddly, if I substitute "folder.FolderID" with "null" (in the linq code), it does return 6 records. So, obviously there's a difference between "null" and an object with a null value. I just don't know what is it and how to fix this.

FYI, I had the code so that the where clause looked like this:

where j.jobmst_type != 1 && j.jobmst_prntid == folder.FolderID

But it didn't produce any results either.

Any help would be appreciated.

Answer 1

As I already mentioned it in a comment: Compare nullable types in Linq to Sql

The answer to that question also applies here: Linq to SQL behaves kind of strangely when querying nullable types. The solution is to check for null explicitly if the value of the nullable type is null . If you don't want to write two queries, just write different where clauses (you have to mix in some lambda syntax):

Expression<Func<Job,bool>> predicate;
if(folder.FolderID == null) {
    predicate = j=>j.jobmst_prntid == null && j.jobmst_type != 1;
} else {
    predicate = j=>j.jobmst_prntid == folder.FolderID && j.jobmst_type != 1;
}

//...
.Where(predicate)
select new
{
    // ...
}

Answer 2

I think you have to prepend (int ?) in the expression to work when you have null

j.jobmst_prntid.Equals ( folder.FolderID )
j.jobmst_prntid.Equals ( (int ? ) folder.FolderID )

For more reference: https://msdn.microsoft.com/en-us/library/bb882535.aspx

or you can try this

 where j.jobmst_type != 1 && j.jobmst_prntid.Equals(folder.FolderID== null ?   null : folder.FolderID)

Answer 3

I ended up doing this for my situation:

List<Job> folderJobs = new List<Job>();
var tidalJobs = (dynamic) null;
if (folder.FolderID == 0)
{
    tidalJobs = from 
                    master in tidal.jobmsts
                join
                    detail in tidal.jobdtls
                on
                    master.jobdtl_id equals detail.jobdtl_id
                where 
                    master.jobmst_prntid.HasValue == false && master.jobmst_type != 1
                select new
                {
                    JobID = master.jobmst_id,
                    JobName = master.jobmst_name,
                    Description = master.jobmst_desc == null ? string.Empty : master.jobmst_desc,
                    Source = detail.jobdtl_cmd == null ? string.Empty : detail.jobdtl_cmd
                };
}
else
{
    tidalJobs = from
                    master in tidal.jobmsts
                join
                    detail in tidal.jobdtls
                on
                    master.jobdtl_id equals detail.jobdtl_id
                where 
                    master.jobmst_prntid == folder.FolderID && master.jobmst_type != 1
                select new
                {
                    JobID = master.jobmst_id,
                    JobName = master.jobmst_name,
                    Description = master.jobmst_desc == null ? string.Empty : master.jobmst_desc,
                    Source = detail.jobdtl_cmd == null ? string.Empty : detail.jobdtl_cmd
                };
}

foreach (var folderJob in tidalJobs)
{
    ...
}

In short, var tidalJobs = (dynamic) null and .HasValue == false is what I needed to get this working. The only caveat is that setting a var to (dynamic) null disables intellisense b/c everything is evaluated at runtime. So, your typing better be spot on.