protected function addSingleRelation(string $relation)
    {
        if (!in_array($relation, $this->singleRelations)) {
            $this->singleRelations[] = $relation;
        }
    }
protected function addSingleRelation(string $relation)
    {
        if (!in_array($relation, $this->singleRelations)) {
            $this->singleRelations[] = $relation;
        }
    }
protected function addSingleRelation ( string $ relation ) { if ( ! in_array ( $ relation , $ this -> singleRelations ) ) { $ this -> singleRelations [ ] = $ relation ; } }
Add a single relation method name once.

@param string $relation
Add a single relation method name once .