How to add foreign key in rails migration with different table name

Question

How can I assign different table name with adding foreign key. for e.g

I have a model like

class MyPost < ActiveRecord::Base   has_many :comments, class_name: PostComment end  class PostComment < ActiveRecord::Base   belongs_to :post, class_name: MyPost end 

Now i want to change my migration file like this:

class CreatePostComments < ActiveRecord::Migration   def change     create_table :post_comments do |t|      t.belongs_to :post, index: true      t.timestamps null: false     end     add_foreign_key :post, :class_name => MyPost   end end  

But it is not working. Migration is getting cancelled. How do I change my migration file to work with my model structure.

Answer 1

You can pass in options for the foreign key as following:

class CreatePostComments < ActiveRecord::Migration   def change     create_table :post_comments do |t|       t.references :post, foreign_key: { to_table: :my_posts }, index: true       t.timestamps null: false     end   end end 

This is also true for the index option if you like to add a unique constraint:

t.references :post, foreign_key: { to_table: :my_posts }, index: { unique: true} 

By the way, references is an alias for belongs_to, or to be more exact, belongs_to is an alias for references.

See the details in the implementation rails 5.0.rc2 & rails 4.2

Answer 2

It should look like this:

class CreatePostComments < ActiveRecord::Migration   def change     create_table :post_comments do |t|      t.belongs_to :post, index: true      t.timestamps null: false     end     add_foreign_key :post_comments, :my_posts, column: :post_id   end end  

Take a look at the documentation: http://apidock.com/rails/ActiveRecord/ConnectionAdapters/SchemaStatements/add_foreign_key

You use the column option when the column is named differently.