src/Adapter/AbstractResourceAdapter.php
protected function isFillableRelation($field, $record)
    {
        return $this->isRelation($field) && $this->isFillable($field, $record);
    }
protected function isFillableRelation($field, $record)
    {
        return $this->isRelation($field) && $this->isFillable($field, $record);
    }
Is the field a fillable relation?

@param $field
@param $record
@return bool