With polymorphic associations, a model can belong to more than one other model, on a single association. For example, you might have a photo model that belongs to either a Site model or a Post model. Here’s how this could be declared:

var Site = bookshelf.Model.extend({
  tableName: 'sites',
  photo: function() {
    return this.morphOne(Photo, 'imageable');

var Post = bookshelf.Model.extend({
  tableName: 'posts',
  photos: function() {
    return this.morphMany(Photo, 'imageable');

var Photo = bookshelf.Model.extend({
  tableName: 'photos',
  imageable: function() {
    return this.morphTo('imageable', Site, Post);

Optionally, if you wish to use column names other than the name suffixed with _type and _id (for example, if you use a different naming convention in your database), you may specify custom columnNames. This argument, when specified, expects an array containing the substitute _type and _id columns, respectively.

Note that any custom columnNames must be specified on both ends of the relationship! Examples are provided for each of the polymorphic relationship types individually.