public function where($flag, $value = null)
    {
        if (!in_array(strtolower($flag), static::$searchCriteria)) {
            throw new InvalidArgumentException("Invalid where criteria '{$flag}'");
        }

        $this->where[$flag] = $value;
        return $this;
    }
public function where($flag, $value = null)
    {
        if (!in_array(strtolower($flag), static::$searchCriteria)) {
            throw new InvalidArgumentException("Invalid where criteria '{$flag}'");
        }

        $this->where[$flag] = $value;
        return $this;
    }
public function where ( $ flag , $ value = null ) { if ( ! in_array ( strtolower ( $ flag ) , static :: $ searchCriteria ) ) { throw new InvalidArgumentException ( "Invalid where criteria '{$flag}'" ) ; } $ this -> where [ $ flag ] = $ value ; return $ this ; }
Set where condition.

@param  string $flag
@param  string $value
@return $this
Set where condition .