Reduce If Statements For MySQL Query

Question

I know there are duplicates of this question, and the answer was to refactor the code.

However I'm not sure where to begin with this particular function.

I'm practising my OOP API skills in PHP5 and decided to write my own little Database API.

I have a function with 4 nested if statements, Im not even sure if 4 nested if's are a lot.

But this piece of code just seems messy to me and was wondering if anybody could provide any tips of how to optimise, reduce if's etc.

How would this kind of function be written in a real-world scenario?

My Code Follows:

public function custom_query( $sql_query_string, $single_column = false){

    $link = $this->_Link_ID;

    // IF LINK IS VALID RESOURCE
    if ( is_resource( $link ) ) {

        $query_resource = mysql_query( $sql_query_string, $link );

        // IF QUERY WAS VALID
        if ( is_resource( $query_resource ) ) {

            $this->_Query_ID = $query_resource;

            $row_count = mysql_num_rows( $query_resource );

            // IF $ROW_COUNT IS A NUMBER, VALID ROWS WERE FOUND
            if ( is_numeric( $row_count ) ) {

                if ( $single_column ){

                    $result_set = mysql_fetch_assoc( $query_resource );
                    return $result_set;
                }

                else {

                    $result_set = array();
                    for ( $row = 0; $row < $row_count; $row++ ) {
                        $result_set[$row] = mysql_fetch_assoc( $query_resource );
                    }
                    return ( object ) array ( 'row_count' => $row_count, 'result_set' => $result_set );
                }
            }

            else {
                die( "Failed To Retrieve Row Count Query: $sql_query_string MySQL Error: " . mysql_error( $link ) );
            }
        }
        else {
            die( "Invalid Query : $query_string. MySql : " . mysql_error( $link ) );
        }
    }
    else {
        die( "Query attempted without valid link resource.  Query : $query_string" );
    }
}

Thanks,

Alex

Answer 1

Since you don't have a problem with die -ing in the middle of the function, you can save some intendation space by simply negating the if s:

public function custom_query( $sql_query_string, $single_column = false){

    $link = $this->_Link_ID;

    // IF LINK IS VALID RESOURCE
    if ( !is_resource( $link ) ) die( "Query attempted without valid link resource.  Query : $query_string" );

    $query_resource = mysql_query( $sql_query_string, $link );

    // IF QUERY WAS VALID
    if ( !is_resource( $query_resource ) ) die( "Invalid Query : $query_string. MySql : " . mysql_error( $link ) );

    $this->_Query_ID = $query_resource;

    $row_count = mysql_num_rows( $query_resource );

    // IF $ROW_COUNT IS A NUMBER, VALID ROWS WERE FOUND
    if ( !is_numeric( $row_count ) ) die( "Failed To Retrieve Row Count Query: $sql_query_string MySQL Error: " . mysql_error( $link ) );

    if ( $single_column ) {

        $result_set = mysql_fetch_assoc( $query_resource );
        return $result_set;
    }

    else {

        $result_set = array();
        for ( $row = 0; $row < $row_count; $row++ ) {
            $result_set[$row] = mysql_fetch_assoc( $query_resource );
        }
        return ( object ) array ( 'row_count' => $row_count, 'result_set' => $result_set );
    }
}

Answer 2

If you decide to stop using die() in your function you can rewrite your code to form:

class Yours {
  protected $errno = 0;
  protected $error = '';

  public function custom_query( $sql_query_string, $single_column = false){

    $link = $this->_Link_ID;

    // IF LINK IS VALID RESOURCE
    if ( !is_resource( $link ) ){
       $this->error = "Query attempted without valid link resource.  Query : $query_string";
       $this->errno = -1;
       return null;
    }
    ...
  }

}

Or you can use exceptions;

  public function custom_query( $sql_query_string, $single_column = false){

    $link = $this->_Link_ID;

    // IF LINK IS VALID RESOURCE
    if ( !is_resource( $link ) ){
       throw new Exception( "Query attempted without valid link resource.  Query : $query_string", -1);
    }
    ...
  }

I personally would go for exceptions... But I guess there are people that disagree with me and I'd like to read their arguments.

EDIT Exception example. We'll extend php Extension class :

class DbException {
  protected $sql;

  public __construct( $message = "", $code = 0, $sql = '', $previous = NULL){
    parent::__construct( $message, $code, $previous);
    $this->sql = $sql;
  }

  public function getSql(){
    return $this->sql;
  }
}

// In model:
throw new DbException( "Query attempted without valid link resource.", -1, $query);

// In main application:
try {
  ob_start();
  // run whole application
} catch( DbException &e){
  ob_clean(); // Suppress all output so far

  echo "<html><body><div class="error">" . htmlspecialchars( $e->getMessage()) . "</div>";
  if( NOT_IN_PRODUCTION){
    echo "<div class='sql'>" . htmlspecialchars( $e->getSql()) . "</div>";
  }
  echo "</body></html>";
}

Exceptions:

• provide backtrace (for easy debugging)
• can be caught by type (and therefore you can handle them in appropriate place or let them propagate to main application)
• can contain additional info for better debugging