Effective use of the Rails has_and_belongs_to_many association

Just a note to myself and others using the Rails has_and_belongs_to_many association:

• The naming of the association table is by alphabetical convention. For example, a many-to-many relationship between Assemblies and Parts models would result in an association table named assemblies_parts. The migration will look like:

  class CreateAssembliesPartsAssociationTable < ActiveRecord::Migration
  
      def self.up
          create_table :assemblies_parts, :id => false do |t|
              t.integer :assembly_id, :null => false
              t.integer :part_id, :null => false
          end
  
          add_foreign_key(:assemblies_parts, :assemblies)
          add_foreign_key(:assemblies_parts, :parts)
      end
  
      def self.down
          drop_table :assemblies_parts
      end
  
  end
  		

  Note that I am using the foreigner gem to implement foreign keys in my migrations.
• Use this association type when you want a direct many-to-many mapping of models without any intervening association model.
• The model mapping looks like the following:

  class Assembly < ActiveRecord::Base
  
      has_and_belongs_to_many :parts
  end
  

  and

  class Part < ActiveRecord::Base
  
      has_and_belongs_to_many :assemblies
  end
  

I just got caught by the alphabetically ordering of the association table name. Thought I would write something up about it.