Add association (<<) without committing to database

Question

Is it possible in Rails to add an association to an existing record without immediately committing this change to the database? E.g. if I have Post has_many :ta

Answer 1

This should work in Rails 3.2 and Rails 4:

post.association(:tags).add_to_target(Tag.first)

See this gist: https://gist.github.com/betesh/dd97a331f67736d8b83a

Note that saving the parent saves the child and that child.parent_id is NOT set until you save it.

EDIT 12/6/2015: For a polymorphic record:

post.association(:tags).send(:build_through_record, Tag.first)
# Tested in Rails 4.2.5