Help me understand "LINQ to Entities only supports casting Entity Data Model primitive types"
I have a unit of work and a repository using EF 4 and POCOs. Since EF requires an ordered set before it can Skip() and Take(), I added the following unit test (without mocks) just to pull out a record to see if it worked.
var myList = UOW.EntityRepo.Get( orderbyLambda: p => p.ID, page: 1, pageSize: 1);
This results in an expression of orderbyLambda = {p => Convert(p.ID)}
and an error during enumeration. The ID is a tinyint
(Int16 / short)
So why does this fail to order by the ID? More about the error
Unable to cast the type 'System.Int16' to type 'System.Object'.
I define the orderbyLambda as Expression<Func<E, object>> orderbyLambda
EDIT:
The real killer is if I do this:
or开发者_StackOverflow中文版derbyLambda: p => new { p.ID }
It works... Why?
It is spotting "order by {object}" and panicking; it knows how to order by string
, int
, short
, DateTime
, etc - but object
is a bit too vague.
You're going to need the actual lambda to be typed correctly; the simplest approach would be to make Get
generic, i.e.
.... Get<TIdentity>(
Expression<Func<E, TIdentity>> orderbyLambda, int page, int pageSize)
and then:
orderbyLambda: p => p.ID
should (without you changing the code at the caller) automatically make that a Get<short>(...)
in this case via generic type inference. The other option is to leave it as <E,object>
, but re-write the expression tree at the receiver. More work.
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