php: sql-query - avoid error

Question

i've wrote a little database class which goes like this:

class dbClass extends mysqli
{
    public function execute($sq)
    {
    $res = parent::query($sq);
    $rs = $res->fetch_array();
    return $rs; 
    }
}

works so far, but the poblem is when running a delete query ("delete from mytable where..") the class throws an error on that line: $rs = $res->fetch_array(); (as it doesn't return anything i guess)

the question is: how can i trap this error? it should simple not do fetch_array() on queries like insert, delete, update ..

thanks!

one option to transfer to function an action like delete , and according to that do not do a fetch_array, another option is to separate function to each action — Haim Evgi
– Haim Evgi, Commented Apr 27, 2011 at 6:52
Are you only planning to get the first row returned by the query, or do you want an array containing all the rows from the query? — Gary Barnett
– Gary Barnett, Commented Apr 27, 2011 at 7:04

Shakti Singh · Accepted Answer · 2011-04-27 06:54:24Z

3

For other type of SQL statements, INSERT, UPDATE, DELETE, DROP, etc, mysql_query() returns TRUE on success or FALSE on error.

you must check the type of result if it is boolean type do not fetch.

And the other solution could be send addition parameter which holds type of query and check that type before fetching.

    public function execute($sq)
    {
      $res = parent::query($sq);
      if (is_bool($res))
      {
       //not to fetch
      }
      else
      {
        $rs = $res->fetch_array();
      }

      return $rs; 
    }

answered Apr 27, 2011 at 6:54

Shakti Singh

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Comments

DhruvPathak · Accepted Answer · 2011-04-27 06:54:28Z

1

what is parent::query code ?

You can just check if the array is present using isset in your fetch_array() function, and return empty array or null if it is not set.

answered Apr 27, 2011 at 6:54

DhruvPathak

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Comments

Sander Marechal · Accepted Answer · 2011-04-27 06:57:24Z

0

Other PHP libraries use two different functions. PHP's PDO for example uses PDO::query for queries that return a result set (i.e. SELECT) and PDO::exec for queries that do not return any results, aside from the number of affected rows (i.e. UPDATE, DELETE, etcetera).

answered Apr 27, 2011 at 6:57

Sander Marechal

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Comments

Emil Vikström · Accepted Answer · 2011-04-27 06:59:33Z

0

As have already been mentioned, the query function does not return a resultset on write queries.

When you write your own db class, take the chance to differentiate between write and read queries. Make them into different functions. That way you can more easily scale up using simple master-slave replication of the database, since you always want to write to the master but read from one of the slaves. You also make it easier to switch to other database extensions, like PDO.

answered Apr 27, 2011 at 6:59

Emil Vikström

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Comments

Ben · Accepted Answer · 2011-04-27 07:03:30Z

0

I'm guessing $res returns null in that case, so test for that:

$res ? $rs = $res->fetch_array() : $rs = $res;

edited Apr 27, 2011 at 7:03

answered Apr 27, 2011 at 6:54

Ben

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2 Comments

Emil Vikström Over a year ago

No, the same code will not work. What happens when $res is "true"?

Ben Over a year ago

You're right. Edited to reflect that. Code only works if $res returns null or an array.

Gary Barnett · Accepted Answer · 2011-04-27 07:57:35Z

I'd warn strongly against a function that has no error checking in it. So here's my suggestion - this code will return an array in every case. If there's an error the array will only have one row containing "Error" in dimension [0] and the error message in dimension [1].

If the query doesn't return a result, the code will return [0] = "OK" and [1] = the number of rows affected.

If the query does return a result, the code will build a resultset containing the returned rows.

$retarray = array();

    $result = $mysqli->query($sq);
    if (!$result) {
       $err = $mysqli->error;
       echo $err;
        $retarray = array(array("Error",$err));

        return $retarray;
    }else {
        if (is_bool($result)){
            $retarray = array(array("OK",$mysqli->affected_rows));

        return $retarray;
        }else{
             while ($row = $result->fetch_array()) {
            array_push($retarray,$row);
        }
        }

        $result->close();
        return $retarray;
    }

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