Why are anonymous Types in EF4 different from LINQ to SQL ones? - entity-framework

Question

I have the following query in LINQ to SQL to fetch all records from a Table that are not already in a jointable.
// <param name="id">The ID of the Person</param>
IEnumberable<object> GetUnassignedClients(int id)
{
_db.Clients
.Select(i => new
{
Client_id = i.Id,
Person_id = id,
Cid = id + "." + i.Id // Please don't ask why I do this. I just have to do it
// ... some more fields
})
.Where(o =>
!_db.Clients_Persons
.Where(t => t.Person_id == id)
.Select(t => t.Client_id)
.Contains(o.Client_id))
.Distinct().ToList();
}
Now I have started a migration to EF4 but the "Cid" part of the anonymous type with the combination ToList() (ToList() triggered the exception is a simplified testcase without the WHERE condition) fails with the exception:
Unable to create a constant value of
type 'System.Object'. Only primitive
types ('such as Int32, String, and
Guid') are supported in this context.
Why is that so or am I missing something here?

Answer 1

EF does not know how to translate the expression id + "." + i.Id into valid SQL which is why it fails. You have to tell EF that it needs to convert id from an integer to a string. You can do this using the SqlFunctions class in the following way:
var ret = _db.Clients
.Select(i => new
{
Client_id = i.Id,
Person_id = id,
Cid = SqlFunctions.StringConvert((double) id) + "." + SqlFunctions.StringConvert((double) i.Id) // Please don't ask why I do this. I just have to do it
// ... some more fields
})
.Where(o =>
!_db.Clients_Persons
.Where(t => t.Person_id == id)
.Select(t => t.Client_id)
.Contains(id)
)
.Distinct()
.ToList()
;