code: protected function loadForeignDataItems()
      {
          $this->_foreignDataItems = [];
          if ($this->lazyForeign) {
              $primaryKeys = $this->foreignModel->findPrimaryKeys($this->settings['foreignPullParams']);
              foreach ($primaryKeys as $primaryKey) {
                  $this->createForeignDataItem(null, ['foreignPrimaryKey' => $primaryKey]);
              }
          } else {
              $foreignModels = $this->foreignModel->findAll($this->settings['foreignPullParams']);
              foreach ($foreignModels as $key => $model) {
                  $this->createForeignDataItem($model, []);
              }
          }
      }
docs: Load the foreign data items, either lazily or not.