code: function HasManyBy(model, parent, foreignKey, ownerKey) {
          var _this = _super.call(this, model) /* istanbul ignore next */ || this;
          _this.parent = _this.model.relation(parent);
          _this.foreignKey = foreignKey;
          _this.ownerKey = ownerKey;
          return _this;
      }
docs: Create a new has many by instance.