Generate migration - create join table

问题

I have looked through many SO and google posts for generating migration of join table for has many and belongs to many association and nothing work.

All of the solutions are generating a empty migration file.

I am using rails 3.2.13 and I have two tables: security_users and assignments. These are some of things I have try:

rails generate migration assignments_security_users

rails generate migration create_assignments_security_users

rails generate migration create_assignments_security_users_join_table

rails g migration create_join_table :products, :categories (following the official documentation)

rails generate migration security_users_assignments security_user:belongs_to assignments:belongs_to 

Can anyone tell how to create a join table migration between two tables?

回答1:

Run this command to generate the empty migration file (it is not automatically populated, you need to populate it yourself):

rails generate migration assignments_security_users

Open up the generated migration file and add this code:

class AssignmentsSecurityUsers < ActiveRecord::Migration
  def change
    create_table :assignments_security_users, :id => false do |t|
      t.integer :assignment_id
      t.integer :security_user_id
    end
  end
end

Then run rake db:migrate from your terminal. I created a quiz on many_to_many relationships with a simple example that might help you.

回答2:

To autopopulate the create_join_table command in the command line, it should look like this:

rails g migration CreateJoinTableProductsSuppliers products suppliers

For a Product model and a Supplier model. Rails will create a table titled "products_suppliers". Note the pluralization.

(Side note that generation command can be shortened to just g)

回答3:

I usually like to have the "model" file as well when I create the join table. Therefore I do.

rails g model AssignmentSecurityUser assignments_security:references user:references

回答4:

I believe this would be an updated answer for rails 5

create_table :join_table_name do |t|
  t.references :table_name, foreign_key: true
  t.references :other_table_name, foreign_key: true
end

来源：https://stackoverflow.com/questions/17765249/generate-migration-create-join-table