When I try to join tables
var query =
from foo in db.Foos
from bar in db.Bars
where foo.ID == bar.FooID
where foo.ID == 45
select bar;
Try that instead:
var query =
from foo in db.Foos
join bar in db.Bars on foo.ID equals bar.FooID
where foo.ID == 45
select bar;
Anyway, I suggest you model the relation between Foo and Bar in the EDM designer, this way you don't need an explicit join:
var query =
from foo in db.Foos
where foo.ID == 45
from bar in foo.Bars
select bar;