Unable to create a constant value of type (type) Only primitive types ('such as Int32, String, and Guid') are supported in this context

Question

I\'ve read ALL of:

• Unable to create a constant value of type 'System.Object' in Entity Framework

• Entity Framework - "Unable to

Answer 1

I ran into a similar problem, and instead of IQueryable, I tried using List, and it worked. May be of some help.

Answer 2

It will not work because you want to use local Album in linq-to-entities query. You must either use navigation property on p to get its album:

var query = from p in VisibleObjects.OfType<Photo>()
            where p.Album.Id == alb.Id
            select p;

or you must build complex query with some join between photos and albums. You cannot pass local object and any its relation to the query. Only simple properties can be passed.

Answer 3

I think that EF is trying to convert where a.Photos.Contains(p) into SQL like WHERE p IN (a.Photos), but it doesn't know how to express a.Photos in SQL. The SQL you want probably looks like WHERE p.Id IN (1, 2, 3), so you could try doing that in C#:

static IQueryable<Photo> VisiblePhotos(this Album a)
{
    var photoIds = a.Photos.Select(p => p.Id).ToArray();
    return from p in VisibleObjects.OfType<Photo>() where photoIds.Contains(p.Id) select p;
}

Answer 4

I tried another way around and it worked:

static IQueryable<Photo> VisiblePhotos(this Album a)
{
    return from p in VisibleObjects.OfType<Photo>()
           where p.Albums.Any(alb => a.ID == alb.ID)
           select p;
}

Quite weird to see this works but the other one not. But I'm still wondering why Contains is not working.