One of Many (Polymorphic)

Sometimes a model may have many related models, yet you want to easily retrieve the "latest" or "oldest" related model of the relationship. For example, a User model may be related to many Image models, but you want to define a convenient way to interact with the most recent image the user has uploaded. You may accomplish this using the morphOne relationship type combined with the ofMany methods:

class Post extends Model {
  /**
   * Get the user's most recent image.
   */
  @MorphOneColumn({
    related: Image,
    morphName: 'imageable',
    onQuery: (q) => {
      q.latestOfMany();
    }
  })
  public latestImage;
}

Likewise, you may define a method to retrieve the "oldest", or first, related model of a relationship:

class Post extends Model {
  /**
   * Get the user's oldest image.
   */
  @MorphOneColumn({
    related: Image,
    morphName: 'imageable',
    onQuery: (q) => {
      q.oldestOfMany();
    }
  })
  public oldestImage;
}

By default, the latestOfMany and oldestOfMany methods will retrieve the latest or oldest related model based on the model's primary key, which must be sortable. However, sometimes you may wish to retrieve a single model from a larger relationship using a different sorting criteria.

For example, using the ofMany method, you may retrieve the user's most "liked" image. The ofMany method accepts the sortable column as its first argument and which aggregate function (min or max) to apply when querying for the related model:

class Post extends Model {
  /**
   * Get the user's most popular image.
   */
  @MorphOneColumn({
    related: Image,
    morphName: 'imageable',
    onQuery: (q) => {
      q.ofMany('likes', 'max')
    }
  })
  public bestImage;
}

NOTE

It is possible to construct more advanced "one of many" relationships. For more information, please consult the has one of many documentation).