Question

In my case, I’m deleting from multiple tables using LEFT JOIN and need to provide an array of question ids to delete. The array of question ids is $questions_to_delete.

Not being able to bind an array as a parameter through mysqli is kind of a pain, and I’ve looked through a few SO questions to arrive at this:

$params = implode(',', array_fill(0, count($questions_to_delete), '?'));
$types = array_fill(0, count($questions_to_delete), 'i');
$delete_questions = $mysqli->prepare('DELETE    ...
                                          FROM questions
                                          LEFT JOIN ...
                                          WHERE questions.id IN ('.$params.')');

call_user_func_array(array(&$delete_questions, 'bind_param'), array_merge($types, $questions_to_delete));
$delete_questions->execute();
$delete_questions->close();

The error I’m getting is

Warning: mysqli_stmt::bind_param() [mysqli-stmt.bind-param]: Number of elements in type definition string doesn’t match number of bind variables

I noticed that some answers used &$delete_questions versus $delete_questions, but I’m stumped as to what PHP is complaining about.

Answer 1

I wasn’t merging $types and $questions_to_delete correctly! In my original code:

// Produces ['i', 'i', 'i', ...]
$types = array_fill(0, count($questions_to_delete), 'i');

// The argument (array_merge) is then ['i', 'i', ..., 'id1', 'id2', ...]
call_user_func_array(array($delete_questions, 'bind_param'), array_merge($types,$questions_to_delete));

What eventually worked for me was:

// Produces 'iii..'
$types = str_repeat('i', $questions_to_delete);

// The argument (array_merge) is then ['iii...', 'id1', 'id2', ...]
call_user_func_array(array($delete_questions, 'bind_param'), array_merge(array($types),$questions_to_delete));

So the types of the parameters need to be a String at the beginning of the parameters array.

I don’t really understand how call_user_func_array handles array(mysqli_stmt, 'bind_param') as a callable, or why the parameters have to be constructed this way, and I’d like to see if anyone can come up with an explanation!