Internal .NET Framework Data Provider error 1025

IQueryable<Organization> query = context.Organizations;

Func<Reservation, bool> predicate = r => !r.IsDeleted;

query.Select(o => new { 
    Reservations = o.Reservations.Where(predicate)
}).ToList();

this query throws "Internal .NET Framework Data Provider error 1025" exception but the query below does not.

query.Select(o => new { 
    Reservations = o.Reservations.Where( r => !r.IsDeleted)
}).ToList();

I need to use the first one because I need to check a few if statements for constructing the right predicate. I know that I can not use if statements in this circumstance that is why I pass a delegate as parameter.

How can I make the first query work?

While the above answers are true, note that when trying to use it after a select statement one has to call AsQueryable() explicitly, otherwise the compiler will assume that we are trying to use IEnumerable methods, which expect a Func and not Expression<Func>.

This was probably the issue of the original poster, as otherwise the compiler will complain most of the time that it is looking for Expression<Func> and not Func.

Demo: The following will fail:

MyContext.MySet.Where(m => 
      m.SubCollection.Select(s => s.SubItem).Any(expr))
         .Load()

While the following will work:

MyContext.MySet.Where(m => 
      m.SubCollection.Select(s => s.SubItem).AsQueryable().Any(expr))
         .Load()

After creating the bounty (rats!), I found this answer, which solved my problem. (My problem involved a .Any() call, which is a little more complicated than this question...)

In short, here's your answer:

IQueryable<Organization> query = context.Organizations;

Expression<Func<Reservation, bool>> expr = r => !r.IsDeleted;

query.Select(o => new { Reservations = o.Reservations.Where(expr) })
  .ToList();

Read the referenced answer for an explanation of why you need the local variable expr, and you can't directly reference another method of return type Expression<Func<Reservation, bool>>.

Thanks for pinging me. I guess I was on the right track after all.

Anyway, to reiterate, LINQ to Entities (thanks to Jon Skeet for correcting me when I got mixed up in my own thought process in the comments) operates on Expression Trees; it allows for a projection to translate the lambda expression to SQL by the QueryProvider.

Regular Func<> works well for LINQ to Objects.

So in this case, when you're using the Entity Framework, any predicate passed to the EF's IQueryable has to be the Expression<Func<>>.

I just experienced this issue in a different scenario.

I have a static class full of Expression predicates which I can then combine or pass to an EF query. One of them was:

    public static Expression<Func<ClientEvent, bool>> ClientHasAttendeeStatus(
        IEnumerable<EventEnums.AttendeeStatus> statuses)
    {
        return ce => ce.Event.AttendeeStatuses
            .Where(a => a.ClientId == ce.Client.Id)
            .Select(a => a.Status.Value)
            .Any(statuses.Contains);
    }

This was throwing the 1025 error due to the Contains method group call. The entity framework expected an Expression and found a method group, which resulted in the error. Converting the code to use a lambda (which can be implicitly cast to an Expression) fixed the error

    public static Expression<Func<ClientEvent, bool>> ClientHasAttendeeStatus(
        IEnumerable<EventEnums.AttendeeStatus> statuses)
    {
        return ce => ce.Event.AttendeeStatuses
            .Where(a => a.ClientId == ce.Client.Id)
            .Select(a => a.Status.Value)
            .Any(x => statuses.Contains(x));
    }

---

Aside: I then simplified the expression to ce => ce.Event.AttendeeStatuses.Any(a => a.ClientId == ce.Client.Id && statuses.Contains(a.Status.Value));

Had a similar problem. Library of ViewModels that look like this:

public class TagViewModel
{
	public int Id { get; set; }
	public string Name { get; set; }

	public static Expression<Func<SiteTag, TagViewModel>> Select = t => new TagViewModel
	{
		Id = t.Id,
		Name = t.Name,
	};

This works:

var tags = await db.Tags.Take(10).Select(TagViewModel.Select)
	.ToArrayAsync();

But, this won't compile:

var post = await db.Posts.Take(10)
	.Select(p => new {
		Post = p,
		Tags = p.Tags.Select(pt => pt.Tag).Select(TagViewModel.Select)
	})
	.ToArrayAsync();

Because the second .Select is a mess - the first one is actually called off of an ICollection, which is not IQueryable, so it consumes that first Expression as a plain Func, not Expression<Func.... That returns IEnumerable<..., as discussed on this page. So .AsQueryable() to the rescue:

var post = await db.Posts.Take(10)
	.Select(p => new {
		Post = p,
		Tags = p.Tags.Select(pt => pt.Tag).AsQueryable()
			.Select(TagViewModel.Select)
	})
	.ToArrayAsync();

But that creates a new, weirder problem: Either I get Internal Framework...Error 1025, or I get the post variable with a fully loaded .Post property, but the .Tags property has an EF proxy object that seems to be used for Lazy-Loading.

The solution is to control the return type of Tags, by ending use of the Anonymous class:

public class PostViewModel
{
	public Post Post { get; set; }
	public IEnumerable<TagViewModel> Tags { get; set; }

Now select into this and it all works:

var post = await db.Posts.Take(10)
	.Select(p => new PostViewModel {
		Post = p,
		Tags = p.Tags.Select(pt => pt.Tag).AsQueryable()
			.Select(TagViewModel.Select)
	})
	.ToArrayAsync();