Question

LINQ to Entities allows this:

context.User.Select(u => new Person
{
    Name = u.Name,
    Parent = u.Parent.Name
});

I need only two properties of a big User table and I get them using the Select method to create a Person object so I can do some processing with it. The thing is that I do this a lot (like twice a second) and it hurts the GC.

So I decided to pool the Person objects but I have no idea how to update an existing object using LINQ to Entities. I can get it as an anonymous method like above and then assign its properties to the depooled object I guess, then I can return the depooled instance, this would at least make the anonymous instance go away in a lower generation of GC but…

I’d really prefer something like this:

context.User.Select(u => People.Take(u.Name, u.Parent.Name))

Which throws a NotSupportedException.

• Can I use Entity Framework to update the values of an existing object?
• If so, how?
• If not, what alternatives do I have?

Answer 1

Can I use Entity Framework to update the values of an existing object?

No – the Select method is used for projection not updating – what your doing is the correct approach. Alternatively you may find it more efficient to change your Person class to a struct as it consumes less memory.

I think you need to elaborate a little more on “It hurts the GC“.

Update

It appears Linq to Entities does not support projecting onto struct‘s (seems like a limitation to me) – best possible approach then would be to just project onto an anonymous type & then you can map your results onto your Person class using your pooling mechanism e.g.

var users = (from u in context.User
            select new {
                Name = u.Name,
                Parent = u.Parent.Name
            }).ToList().Select(u => People.Take(u.Name, u.Parent));