Generating a model with many to many in Ruby on Rails

Question

Is there a way to generate a Rails model with a many to many relationship predefined? I know how to add it to the Active Record after the fact but it would be nice to have it defined in the DB migration and the Active Record model right off the bat.

Answer 1

Remember that you do not want an id for the join table, so make sure to add :id => false |t|

create_table assemblies_parts, :id => false do |t|
  t.integer :assembly_id
  t.integer :part_id
end

If you use rails

rails generate model Assemblies_parts assembly:references part:references

you will have two indexes, but what you want is

# Add table index
add_index :assemblies_parts, [:assembly_id, :part_id], :unique => true

UPDATE

• For Rails 5 use create_join_table instead to create that (id-less) table.

Answer 2

You can use this reference from the Rails Guides.Here is the link. Also you will need to manually create the join table for those models using a migration.

e.g

    create_table :assemblies_parts, :force => true do |t|
      t.integer :assembly_id
      t.integer :part_id
    end

Answer 3

Please look at this question first: Creating a many-to-many relationship in Rails 3.

In addition, I would recommend next book "Ruby on Rails 3 Tutorial: Learn Rails by Example" for a better understanding of ActiveRecord relations.