Casting LINQ expression throws "Internal .NET Framework Data Provider error 1025."
c#, entity-framework, linq
Solution
You want to "store [the] expression in a variable, for reuse purposes, and pass that into `Count()`". This is 100% possible if the `Expression` can be translated to SQL. The problem here is that you're introducing something that can't be translated to SQL. The particular issue in this case is that the cast gets translated to an `Expression.Convert`. Your types definitely aren't represented in SQL, so this won't be able to execute. Plug both into LINQPad and check out the IL to see the difference.
As the other related question/answer you linked to suggests, you need to pass your predicate as an `Expression` rather than a `Func` (how to do the work vs. pointing to a location in code that does the work). The problem, as you noted, is that the `Count` method doesn't take an `Expression`, but this is easily resolved by using `AsQueryable()` which will give you the `IQueryable` extension methods that take `Expression`.
This should have no problems executing:
Expression<Func<Item,bool>> predicate = i => i.Amount.HasValue;
model.Items = dbQuery.Select(c => new Item {
Total = c.Items.AsQueryable().Count(predicate)
}).ToArray();
Problem
The following code: ``` model.Items = dbQuery.Select(c => new Item { Total = c.Items.Count((Func<Item, bool>)(t => t.Amount.HasValue)) }).ToArray(); ``` Throws the following exception: Internal .NET Framework Data Provider error 1025. However the exact code minus the cast works: ``` model.Items = dbQuery.Select(c => new Item { Total = c.Items.Count(t => t.Amount.HasValue) }).ToArray(); ``` Note: `dbQuery` is just an EF `ObjectQuery`. The expected type for `Count()` is `Func<Item, bool>`, and it's even verified by ReSharper that they're the same type by the fact that it grays the cast out, suggesting that it's not needed and they're functionally equivalent. However, the exception proves that they are not, in fact, functionally equivalent. Also, I did see this related question/answer, but `Count()` (in this case, anyway) will not accept an `Expression<Func<Item bool>>`, so that doesn't work for me.