php - PDO alternative to mysql_ for getting field info -

when learned php, learned apparently older guides , have been using mysql_ functions. i'm switching on pdo , have function want keep can't quite figure out how change it. mysql_ function.

function getfield($field){   $query = "select $field users id='".$_session['user_id']."'";   if($query_run = mysql_query($query)){      if ($query_result = mysql_result($query_run, 0, $field)){       return $query_result;      }   }  } 

and can field want. it's using mysql_ stuff hear deprecated , on way out. function gets session id when log in, , using session info, gathers information user.

here quick example of function using pdo. i've left comments in code grasp idea.

function getfield($field) {     // assuming obtained connection here.     // purpose of showing example name database connection variable $db      // first check if have user_id in our session, , sanitize it.     // never query database unsanitized data.      $userid = isset($_session['user_id']) ? filter_var($_session['user_id'], filter_sanitize_number_int) : null;      // if user_id not presented, don't need query database @ all. return null or whatever suits needs     if( ! $userid ) {         return null;     }      // build query     $sql = sprintf(         "select `%s` `users` `id` = :userid limit 1",         $field     );      // prepare statement executed     // more read prepared statements: http://php.net/manual/en/pdo.prepare.php     $query = $db->prepare($sql);      // pass user id our prepared query     // more read binding parameters: http://php.net/manual/en/pdostatement.bindparam.php     $query->bindparam(':userid', $userid);      // execute query     $query->execute();      // return single result     return $query->fetch(pdo::fetch_assoc); } 

if have questions, don't hesitate ask.

- update per op comment -

using above function end getting array result following reasons:

• ->fetch() combined pdo::fetch_assoc option return array single item in if result being found. key in array in case field name.

now can either access value this:

$result = getfield('username'); print $result['username']; 

or in function:

$result = $query->fetch(pdo::fetch_assoc); if( isset($result[ $field ] ) {     return $result[ $field ]; }  return null;