实体框架由孙子实体过滤

Question

If I have the following tables:
Parent : has ParentId
Child : has ChildId and ParentId
Grandchild : has GrandchildId , ChildId and Quantity

Whats the best approach to retrieve a list of Parents where they have a grandchild with quantity greater than 10 (for example)?

I played with linq to entity, generating something like:

context.Parent.Includes("Children").Include("GrandChildren").Where( ... )

But wasn't sure about the syntax, and I wonder about performance- do the includes load up all objects? What's the best way to accomplish this?

Answer 1

Try this:

var query = context.Parents
                   .Where(p => p.Children.Any(
                          c => c.GrandChildren.Any(g => g.Quantity > 10));

Include will indeed load all child and grandchild entities related to loaded parents.

Answer 2

The performance is bad with this approach...

context.Parent.Includes("Children").Include("Children.GrandChildren").Where( ... )

If you need the children and grandchildren at a later point or maybe don't need them at all, try to load them later with:

if (!parent1.ChildrenReference.IsLoaded)    
     parent1.ChildrenReference.Load();