intro

• a model can belong to more than one other models.
• polymorphic belongs_to set up an interface that any other models can use.
  • e.g. Picture model belongs to imageable, Product model as imageable.
  • e.g. Reputation model belongs to reputable, User model as reputable.

basic example

• rails generator
  • rails g picture imageable:references{polymorphic}
  • t.references :imageable, polymorphic: true
    • add columns: :imageable_id and :imageable_type
    • add index: t.index ["imageable_type", "imageable_id"]
• models:
  • belongs_to :imageable, polymorphic: true # Picture
  • has_many :pictures, as: :imageable # User
  • has_many :pictures, as: :imageable # Product
• rails console:
  • @user.pictures
  • @product.pictures
  • @picture.imageable