public function where(string $key, string $operator, $value): QueryBuilder
    {
        $this->addWhere($key, $operator, $value, 'AND');
        return $this;
    }
public function where(string $key, string $operator, $value): QueryBuilder
    {
        $this->addWhere($key, $operator, $value, 'AND');
        return $this;
    }
public function where ( string $ key , string $ operator , $ value ) : QueryBuilder { $ this -> addWhere ( $ key , $ operator , $ value , 'AND' ) ; return $ this ; }
Adds a where condition.

@param string $key
@param string $operator
@param mixed $value
@return QueryBuilder
Adds a where condition .