Linq2Sql: Using IQueryable in select

Question

This is probably quite trivial but.... I have a quite complicated linq query that I have put in a IQueryable function that I'd like to reuse throughout the project. But when I use this in a select I get "System.Linq.IQueryable`1[LINQPad.User.Orders] Foo(System.Guid) doesn't have a translation to SQL": (very simplified to show what I've after)

void Main() { (from e in Clients select new { e.CompanyName, Orders = Foo(e.Id).Count() }).Take(20).Dump(); } IQueryable<Orders> Foo(Guid clientId) { return Orders.Where(e => e.ClientId.Equals(clientId)); }

Doesn't work, but the following does:

void Main() { (from e in Clients select new { e.CompanyName, Orders = Orders.Where(f => f.ClientId.Equals(e.Id)).Count() }).Take(20).Dump(); }

Is there any way I can rewrite the query without rewriting Foo?

Bennor McCarthy · Accepted Answer · 2010-09-16 09:14:36Z

The problem is that you can't just inject a function into your Linq query, because Linq-to-SQL or Linq-to-Entities doesn't know how to translate it. There's a good description of the problem, and a solution available at the LINQPad site.

An alternative is to bring the dataset into memory first (e.g. by using ToList()), but that won't really achieve exactly what you're after.

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