Entity Framework: The argument to DbIsNullExpression must refer to a primitive or reference type

Question

I\'m trying to use entity to do this:

    SELECT *
    FROM aspnet_Users u LEFT JOIN (SELECT u.UserId, p.Permission, p.MediaId, p.Valid
                              


        

Answer 1

I realize that since in the second query,it still have the left join with aspnet_Users table, it does not need to have u in the 1st query, so I changed it to below, it works now. But still, it will be great to know why the original code and suggested code failed.

    var up = from u in en.aspnet_Users
                     join p in en.Permissions
                         on u.UserId equals p.UserId into pu
                     from p2 in pu.DefaultIfEmpty()
                     where p2.MediaId == this.MediaId && p2.Valid == true
                     select p2;

            var ul = from us in en.aspnet_Users
                     join pm in up
                          on us.UserId equals pm.UserId into pm1
                     from pm2 in pm1.DefaultIfEmpty()
                     orderby us.LoweredUserName
                     select new PermissionInfo
                     {
                         Permission = (pm2 == null ? -1 : pm2.Permission1),
                         UserName = us.UserName,
                         UserId = us.UserId,
                         PermissionId = (pm2 == null ? -1 : pm2.PermissionId)
                     };

            ret = ul.ToList();

Answer 2

Had a similar problem, I managed to solve it by moving the null check outside of the sql. In your case you can do it by calling ToList() before checking for Null:

var intermediateUl = from us in en.aspnet_Users
    join pm in up
      on us.UserId equals pm.UserId into pmOuter
    from pm2 in pmOuter.DefaultIfEmpty()
    select new { us.UserName, us.UserId, pm2};

var ul = intermediateUl
    .ToList()
    .Select(o => new PermissionInfo { 
        Permission = (o.pm2 == null ? -1 : pm2.Permission1), 
        PermissionId = (o.pm2 == null ? -1 : pm2.PermissionId) 
        UserName = o.UserName, 
        UserId = o.UserId, 
     });

The problem surprised me as well, because couple lines above I had a similar query with outer join which passed OK. It seems that checking for null with linq outer construct is only possible with entities known by Entity Framework. Any other class, anonymous or not, confuses EF/linq.

I know this question is old, but maybe it will help someone :)