code: function(instance) {
      var updates = _.object([[this.foreignKey, undefined]]);
      var query = this.objectsQuery(instance).update(updates);
      var after = this.afterClearingObjects.bind(this, instance);
      return query.execute().tap(after);
    }
docs: Perform the necessary updates to clear objects for this relation.
  
  This method invalidates the {@link HasMany#objectsQuery}.
  
  Mixins can override {@link HasMany#executeClear} to change the way clears
  are performed when related objects are cleared. This is the default
  implementation.
  
  @method
  @protected
  @param {Model} instance The model instance on which to operate.