#47 Two Many-to-Many

Jun 20, 2007 | 9 minutes | Active Record

There are two different ways to set up a many-to-many association in Rails. In this episode you will see how to implement both ways along with some tips on choosing the right one for your project.

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has_and_belongs_to_many

          ruby
        
# in migration
def self.up
  create_table 'categories_products', :id => false do |t|
    t.column :category_id, :integer
    t.column :product_id, :integer
  end
end

          models/product.rb
        
has_and_belongs_to_many :categories

          models/category.rb
        
has_and_belongs_to_many :products

has_many :through

          models/categorization.rb
        
belongs_to :product
belongs_to :category

          models/product.rb
        
has_many :categorizations
has_many :categories, :through => :categorizations

          models/category.rb
        
has_many :categorizations
has_many :products, :through => :categorizations