title: Seed a has_and_belongs_to_many table relationship
body: <p>I have a project with 2 models linked through a <strong>habtm</strong> relationship and 
  would like to seed the default relationships values as they are fixed and needed for the 
  web aplication to work. </p>
  
  <p>Can't seem to find a way to access the model join table and seed the default values to the object1_id, object2_id as the table is not linked to a model. It's currently being done via SQL directly on postgreSQL.</p>
  
  <p>Any suggestions?</p>