Question

I’m trying to query my EF Model (using ASP.NET MVC WebApi) but only the first version (using SingleOrDefault) works and not the second one and i can’t get my head around it!

Working:

Public Overloads Shared Function GetById(id As Integer) As MEDIA
    Dim db As New EFEntities()
    Dim r As New MEDIA()
    r = db.MEDIA.SingleOrDefault(Function(p) p.id = id)

    Return r
End Function

Not Working:

Error : Unable to cast object of type ‘System.Data.Objects.ObjectQuery`1[Data.MEDIA]’ to type ‘Data.MEDIA’

Public Overloads Shared Function GetById(id As Integer) As MEDIA
    Dim db As New EFEntities()
    r = From media In db.MEDIA
            Where media.id= id _
            Select media

    Return r
End Function        

I would really appreciate it if somebody could show me how to get the second version running and explain what the problem is!

Answer 1

In your first example, the line:

r = db.MEDIA.SingleOrDefault(Function(p) p.id = id)

initializes a single MEDIA object.

In your second example, however, the line:

r = From media In db.MEDIA
        Where media.id= id _
        Select media

initializes a collection of MEDIA objects – incompatible types.

If you changed your return expression in your second example to:

Return r.SingleOrDefault()

and stick Dim in front of the initialization of r it’ll work.