Question

I have a local list of values that I need to have entity framework check against the database and return them.

If the list was already in the database, the following would work:

var list = /* some ef query */;
var myList = context.Logs.Where(l => list.Any(li => l.LogNumber == li.LogNumber));

But if the list is local, it would throw an error:

var list = new List<Log>();
var myList = context.Logs.Where(l => list.Any(li => l.LogNumber == li.LogNumber));

Exception: Unable to process the type 'Data.Log[]', because it has no known mapping to the value layer.

So how can I match a local list against a database list using EF?

Answer 1

I got a different error than you with the code sample, but I believe it’s the same idea. EF doesn’t know how to translate List<Log> into a SQL store expression. It works when you’re still in a query because it hasn’t been serialized yet.

I realize this is less than ideal, but I was able to make this query work by extracting the scalar values of LogNumber and then using that in the query.

    var list = new List<Log>();
    list.Add(new Log()
       {
           LogNumber = 1
       });
    var numbers = list.Select(l => l.LogNumber);
    var myList = m.Logs.Where(l => numbers.Contains(l.LogNumber));