Some command to set up a many to many relationship

has_and_belongs_to_many.txt

# using has_and_belongs_to_many

rails g model mountain name
rails g model climber name

class Climber < ApplicationRecord
	has_and_belongs_to_many :mountains
end

class Mountain < ApplicationRecord
	has_and_belongs_to_many :climbers
end

# using a model...
rails g model climbers_mountains climber:references mountain:references
# ...Rails will create
class CreateClimbersMountains < ActiveRecord::Migration[5.0]
  def change
    create_table :climbers_mountains do |t|
      t.references :climber, foreign_key: true
      t.references :mountain, foreign_key: true

      t.timestamps
    end
  end
end

# using a migration
rails g migration CreateJoinTableClimbersMountains climber mountain
# ...Rails will create this. You must uncomment one of the t.index lines
class CreateJoinTableClimbersMountains < ActiveRecord::Migration[5.0]
  def change
    create_join_table :climbers, :mountains do |t|
      t.index [:climber_id, :mountain_id]
      # t.index [:mountain_id, :climber_id]
    end
  end
end

# then you should execute

$ rake db:create
$ rake db:migrate (or 'rake db:migrate RAILS_ENV=test' for the test environment)
$ rails c
john = Climber.create(name: "John Doe")
udalaitz = Mountain.create(name: "Udalaitz")
john.mountains << udalaitz

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