I have successfully used HABTM to create a many-to-one-to-many set of
rows in one step. Now, if two objects I want to associate already exist,
how do I create the join row? The Agile book mentions the
‘push_with_attributes’ method. The text says this method is useful for
adding additional attributes to the join row (in the example a ‘read_at’
timestamp). I only require a simple two-key join row - is
‘push_with_attributes’ the way to go?