Polymorphic Relationships

A polymorphic relationship allows the target model to belong to more than one type of model using a single association.

MorphOne & MorphMany

Imagine an application where both Post and Video models can have Comments.

Table Structure

posts
    id - integer
    title - string

videos
    id - integer
    title - string

comments
    id - integer
    body - string
    commentable_id - integer
    commentable_type - string

Defining the Relationship

Parent Models:

class Post extends Model {
  MorphMany<Comment> comments() => morphMany(Comment.new, 'commentable');
}

class Video extends Model {
  MorphMany<Comment> comments() => morphMany(Comment.new, 'commentable');
}

Child Model (Inverse):

class Comment extends Model {
  MorphTo<Model> commentable() => morphToTyped('commentable', {
    'posts': Post.new,
    'videos': Video.new,
  });
}

Note: In the MorphTo definition, you must provide a map connecting the table names (stored in commentable_type) to the Model factories.

MorphToMany

A many-to-many polymorphic relation allows a model to belong to many other models of different types via a pivot table. A common example is Tags that can be applied to Posts and Videos.

Table Structure

posts
    id - integer
    title - string

videos
    id - integer
    title - string

tags
    id - integer
    name - string

taggables (pivot table)
    tag_id - integer
    taggable_id - integer
    taggable_type - string

Defining the Relationship

Inverse (Tag):

class Tag extends Model {
  MorphToMany<Post> posts() => morphToMany(Post.new, 'taggable');
  MorphToMany<Video> videos() => morphToMany(Video.new, 'taggable');
}

Owning Side:

class Post extends Model {
  MorphToMany<Tag> tags() => morphToMany(Tag.new, 'taggable');
}