Variable parameter/result binding with prepared statements

Question

In a project that I'm about to wrap up, I've written and implemented an object-relational mapping solution for PHP. Before the doubters and dreamers cry out "how on earth?", relax -- I haven't found a way to make late static binding work -- I'm just working around it in the best way that I possibly can.

Anyway, I'm not currently using prepared statements for querying, because I couldn't come up with a way to pass a variable number of arguments to the bind_params() or bind_result() methods.

Why do I need to support a variable number of arguments, you ask? Because the superclass of my models (think of my solution as a hacked-up PHP ActiveRecord wannabe) is where the querying is defined, and so the find() method, for example, doesn't know how many parameters it would need to bind.

Now, I've already thought of building an argument list and passing a string to eval(), but I don't like that solution very much -- I'd rather just implement my own security checks and pass on statements.

Does anyone have any suggestions (or success stories) about how to get this done? If you can help me solve this first problem, perhaps we can tackle binding the result set (something I suspect will be more difficult, or at least more resource-intensive if it involves an initial query to determine table structure).

Answer 1

The more modern way to bind parameters dynamically is via the splat/spread operator (...).

Assuming:

• you have a non-empty array of values to bind to your query and
• your array values are suitably processed as string type values in the context of the query and
• your input array is called $values

Code for PHP5.6 and higher:

$stmt->bind_param(str_repeat('s', count($values)), ...$values);

In fact, all of the arguments fed to bind_param() can be unpacked with the splat/spread operator if you wish -- the data types string just needs to be the first element of the array.

array_unshift($values, str_repeat('s', count($values)));
$stmt->bind_param(...$values);

Answer 2

You've got to make sure that $array_of_params is array of links to variables, not values themselves. Should be:

$array_of_params[0] = &$param_string; //link to variable that stores types

And then...

$param_string .= "i";
$user_id_var = $_GET['user_id'];//
$array_of_params[] = &$user_id_var; //link to variable that stores value

Otherwise (if it is array of values) you'll get:

PHP Warning: Parameter 2 to mysqli_stmt::bind_param() expected to be a reference

---

One more example:

$bind_names[] = implode($types); //putting types of parameters in a string
for ($i = 0; $i < count($params); $i++)
{
   $bind_name = 'bind'.$i; //generate a name for variable bind1, bind2, bind3...
   $$bind_name = $params[$i]; //create a variable with this name and put value in it
   $bind_names[] = & $$bind_name; //put a link to this variable in array
}

and BOOOOOM:

call_user_func_array( array ($stmt, 'bind_param'), $bind_names); 

Answer 3

In PHP you can pass a variable number of arguments to a function or method by using call_user_func_array. An example for a method would be:

call_user_func_array(array(&$stmt, 'bindparams'), $array_of_params);

The function will be called with each member in the array passed as its own argument.