private function buildFieldsParameter() {
        list($parentEntities, $childrenEntities) = $this->getParentAndChildrenEntities();

        $parameter = new Swagger\Parameter();
        $parameter->setName('fields');
        $parameter->setDescription(
            'Can be fields on this entity, parent entities, or children entities. Specify entities other than this one with type.field. Eligible entities are: '
            . implode(', ', array_merge($parentEntities, $childrenEntities)) . '. Optional.'
        );
        $parameter->setParamType('query');
        $parameter->setType('string');
        $parameter->setAllowMultiple(true);
        return $parameter;
    }