LINQ - IEnumerable.Join on Anonymous Result Set in VB.NET

I've long since built a way around this, but it still keeps bugging me... it doesnt help that my grasp of dynamic LINQ queries is still shakey.

For the example:

Parent has fields (ParentKey, ParentField)

Child has fields (ChildKey, ParentKey,开发者_StackOverflow社区 ChildField)

Pet has fields (PetKey, ChildKey, PetField)

Child has a foreign key reference to Parent on Child.ParentKey = Parent.ParentKey

Pet has a foreign key reference to Child on Pet.Childkey = Child.ChildKey

Simple enough eh?

Lets say I have LINQ like this...

Dim Q = FROM p in DataContext.Parent _
Join c In DataContext.Child On c.ParentKey = p.ParentKey

Consider this a "base query" on which I will perform other filtering actions. Now I want to join the Pet table like this:

Q = Q.Join(DataContext.Pet, _
Function(a) a.c.ChildKey, _
Function(p As Pet) p.ChildKey, _
Function(a, p As Pet) p.ChildKey = a.c.ChildKey)

The above Join call doesnt work. I sort of understand why it doesnt work, but hopefully it'll show you how I tried to accomplish this task.

After all this was done I would have appended a Select to finish the job.

Any ideas on a better way to do this? I tried it with the PredicateBuilder with little success. I might not know how to use it right but it felt like it wasnt gonna handle the joining.

Well, to avoid leaving this unanswered, heres my workaround.

The Join didnt work because the compiler throws a piffy message saying that in that in the last part of the join, either both parameters must be strongly typed, or anonymous.

Function(a, p As Pet) p.ChildKey = a.c.ChildKey) 

Naturally this isnt going to be the case, as my previous query is anonymous, and I'm trying to join it to a typed LINQ class.

I cant just change the type of the variable receiving the query either, because then I can only join on the type that I'm selecting. Like, if I wanna select the Parent based on the pet, then I can only perform my join this way if I'm joining the pet directly to the parent(to my knowledge at least), which can't happen as I have to go through the child to get to the pet.

My solution, was to re-query the same variable, and join on the strong type within the anonymous type.

Dim q = From anon in q _ 
Join p In DataContext.Pet On p.ChildKey = anon.c.ChildKey

That way, I can select the parent based on the pet by appending my where like this:

q = q.Where(Function(v) v.p.PetField = "Fido"

Then the select like this:

q = q.Select(Function(v) v.anon.p)

Ugly right? But it does work.