rails 多対多

rails generate scaffold group name:string

rails generate scaffold menber name:string

rails generate migration group_and_menber







class GroupAndMenber < ActiveRecord::Migration
  def self.up
    create_table :group_and_menbers do |t|
      t.integer :menber_id
      t.integer :group_id
    end
  end

  def self.down
    drop_table :group_and_menbers
  end
end

class GroupAndMenber < ActiveRecord::Base
  belongs_to :menber
  belongs_to :group
end


class Group < ActiveRecord::Base
  has_many :group_and_menbers
  has_many :menbers, :through => :group_and_menbers
end

class Menber < ActiveRecord::Base
  has_many :group_and_menbers
  has_many :groups, :through => :group_and_menbers
end



menber = Menber.new(:name => 'menber1')
menber.save
group = Group.new(:name => 'group1')
group.save  

menber.groups << group

で多対多が成立します