Rails has_and_belongs_to_many migration
You need to add a separate join table with only a restaurant_id
and user_id
(no primary key), in alphabetical order.
First run your migrations, then edit the generated migration file.
Rails 3
rails g migration create_restaurants_users_table
Rails 4:
rails g migration create_restaurants_users
Rails 5
rails g migration CreateJoinTableRestaurantUser restaurants users
From the docs:
There is also a generator which will produce join tables if JoinTable is part of the name:
Your migration file (note the :id => false
; it's what prevents the creation of a primary key):
Rails 3
class CreateRestaurantsUsers < ActiveRecord::Migration
def self.up
create_table :restaurants_users, :id => false do |t|
t.references :restaurant
t.references :user
end
add_index :restaurants_users, [:restaurant_id, :user_id]
add_index :restaurants_users, :user_id
end
def self.down
drop_table :restaurants_users
end
end
Rails 4
class CreateRestaurantsUsers < ActiveRecord::Migration
def change
create_table :restaurants_users, id: false do |t|
t.belongs_to :restaurant
t.belongs_to :user
end
end
end
t.belongs_to
will automatically create the necessary indices. def change
will auto detect a forward or rollback migration, no need for up/down.
Rails 5
create_join_table :restaurants, :users do |t|
t.index [:restaurant_id, :user_id]
end
Note: There is also an option for a custom table name that can be passed as a parameter to create_join_table called table_name
. From the docs
By default, the name of the join table comes from the union of the first two arguments provided to create_join_table, in alphabetical order. To customize the name of the table, provide a :table_name option:
For HABTM relationships, you need to create a join table. There is only join table and that table should not have an id column. Try this migration.
def self.up
create_table :restaurants_users, :id => false do |t|
t.integer :restaurant_id
t.integer :user_id
end
end
def self.down
drop_table :restaurants_users
end
You must check this relationship rails guide tutorials
The answers here are quite dated. As of Rails 4.0.2, your migrations make use of create_join_table
.
To create the migration, run:
rails g migration CreateJoinTableRestaurantsUsers restaurant user
This will generate the following:
class CreateJoinTableRestaurantsUsers < ActiveRecord::Migration
def change
create_join_table :restaurants, :users do |t|
# t.index [:restaurant_id, :user_id]
# t.index [:user_id, :restaurant_id]
end
end
end
If you want to index these columns, uncomment the respective lines and you're good to go!
When creating the join table, pay careful attention to the requirement that the two tables need to be listed in alphabetical order in the migration name/class. This can easily bite you if your model names are similar, e.g. "abc" and "abb". If you were to run
rails g migration create_abc_abb_table
Your relations will not work as expected. You must use
rails g migration create_abb_abc_table
instead.