> like I said Slick is not an ORM whereas Diesel is.

I personally find "ORM" to be such a broad term as to be almost meaningless. This may be a personal problem :)

I see now. I am pretty sure that you could write

  posts.filter(user_id.eq(1)).load(&connection)

if you wanted; the belonging_to is just fancier and a bit shorter.

Anyway, thank you! I've mentally filed a "check out Slick sometime" bug for my infinite personal-to-do list :)