How to rename a model with foreign key constraints in Rails

If you want to change the model name, you don't need to take anything into consideration if you want to change only the corresponding table, but if you have a child model that references the corresponding table, you also need to change the foreign key of the child model. For a project that hasn't been published yet, you can rewrite the existing migration file and do rails db: migrate: reset, but not for a project that already has data.

Model preparation

First, prepare the model. This time, we will prepare the User model and Task model, which are related to User has_many Tasks. To make the contents of the model easier to understand, I will not write any columns other than foreign keys this time.

rails g model User rails g model Task user:references

The above command will create the following two migration files.

db/migration/20201004121521_create_users.rb

class CreateUsers < ActiveRecord::Migration[6.0]
  def change
    create_table :users do |t|

      t.timestamps
    end
  end
end

db/migration/20201004121556_create_tasks.rb

class CreateTasks < ActiveRecord::Migration[6.0]
  def change
    create_table :tasks do |t|
      t.references :user, null: false, foreign_key: true

      t.timestamps
    end
  end
end

rails db: migrate updates schema.rb.

db/schema.rb

ActiveRecord::Schema.define(version: 2020_10_04_121556) do

  create_table "tasks", force: :cascade do |t|
    t.integer "user_id", null: false
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.index ["user_id"], name: "index_tasks_on_user_id"
  end

  create_table "users", force: :cascade do |t|
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  add_foreign_key "tasks", "users"
end

In rails, if you give a reference type, the index will be pasted without permission. Even if you don't set ʻindex: true, t.index ["user_id"], name: "index_tasks_on_user_id" is described. Also, since foreign_key: true was given, ʻadd_foreign_key" tasks "," users " are described.

As mentioned above, the User model and the Task model associated with it have been created.

Change the model name

Now let's change the User model to AdminUser. First, create a migration file that changes the model name normally, and migrate it.

Create the following file with rails g migration RenameUserToAdminUser and rails db: migrate

db/migration/20201004123215_rename_user_to_admin_user.rb

class RenameUserToAdminUser < ActiveRecord::Migration[6.0]
  def change
    rename_table :users, :admin_users
  end
end

Now let's check schema.rb. As you can see, ① user has been renamed to admin_user.

But, (2) The foreign key of the task model remains user_id and has not been renamed. (Speaking of course, of course)

And (3) The foreign key constraint part is linked to admin_user with the column name user_id.

db/schema.rb

ActiveRecord::Schema.define(version: 2020_10_04_123215) do

  create_table "admin_users", force: :cascade do |t| # ←①
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "tasks", force: :cascade do |t|
    t.integer "user_id", null: false # ←②
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.index ["user_id"], name: "index_tasks_on_user_id"
  end

  add_foreign_key "tasks", "admin_users", column: "user_id" # ←③
end

If you check this schema, it seems that a series of corrections will be completed if you change the column name with the foreign key constraint!

Change the external key column name

Now, let's create a migration file that changes the column name. rails g migration RenameUserIdToAdminUserId

db/migration/20201004125441_rename_user_id_to_admin_user_id.rb

class RenameUserIdToAdminUserId < ActiveRecord::Migration[6.0]
  def change
    rename_column :tasks, :user_id, :admin_user_id
  end
end

rails db:migrate

The column name change has been reflected. ④ The user_id of the Task model becomes admin_user_id, (5) The column name of the foreign key is no longer specified.

db/schema.rb

ActiveRecord::Schema.define(version: 2020_10_04_125441) do

  create_table "admin_users", force: :cascade do |t|
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "tasks", force: :cascade do |t|
    t.integer "admin_user_id", null: false # ←④
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.index ["admin_user_id"], name: "index_tasks_on_admin_user_id"
  end

  add_foreign_key "tasks", "admin_users" # ←⑤
end

Summary

To change the model name with a foreign key constraint

1. Change the model name
2. Change the foreign key name for the model

This was all I could do. It was unexpectedly easy. In particular, it was Rails that changed the direction of foreign keys just by changing the model name.