A model can associate with other models by way of a polymorphic association. This can be useful when the associated models are not of the same class but share a common interface, or when a model shares the same type of relationship with multiple other models.
For example, three models Post
, Project
, and Issue
may have many comments.
Instead of creating a different comment model for each of these three models (PostComment
, ProjectComment
…) it would be much more straightforward to have a single Comment
model and establish a relationship to a subject.
create_table :comments do |t|
t.text :body
t.references :subject, polymorhic: true
The subject
could be a Post
, Project
, Issue
or any other model we wish to attach a comment to.
The polymorphic option, instructs the database to store the associated object's type. The above migration creates a :subject_type
column.
The relationships are established in the models like so:
class Comment < ApplicationRecord
belongs_to :subject, polymorphic: true
end
class Post < ApplicationRecord
has_many :comments, as: subject
end
class Project < ApplicationRecord
has_many :comments, as: subject
end
class Issue < ApplicationRecord
has_many :comments, as: subject
end
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