Execute Multiple MySQL Queries using PDO from PHP Post - php

Question

I have a PHP script to post the following data to add-rma-process.php after submission:
$_POST['rmanumber']
$_POST['parent']
$_POST['qty']
However, there are also other fields which are to be posted but will depend on the $_POST['qty'] variable. Say, the $_POST['qty'] = 5 then I will have $_POST['pn1'], $_POST['sn1'], $_POST['rm1'] up to $_POST['pn5'], $_POST['sn5'], $_POST['rm5']. I think you guys get the logic.
Once add-rma-process.php receives these data, I am doing this:
require("common.php");
for($i=0; $i<$_POST['qty']; $i++) {
$count = $i+1; // to start with 1 instead of 0
$query = "INSERT INTO rmadb (rmanumber, parent, childpn, childsn, remarks, user, date) VALUES (:rmanumber, :parent, :childpn, :childsn, :remarks, :user, NOW())";
$query_params = array(
":rmanumber" => $_POST['rmanumber'],
":parent" => $_POST['parent'],
":childpn" => $_POST['pn$count'],
":childsn" => $_POST['sn$count'],
":remarks" => $_POST['rm$count'],
":user" => $_SESSION['user']['fname']." ".$_SESSION['user']['lname']
);
try {
$stmt = $db->prepare($query);
$res = $stmt->execute($query_params);
} catch(PDOException $ex) {
die("Failed to run query: " . $ex->getMessage());
}
}
What I was trying to do is do a for loop to execute the query until the condition is met but it is not working. What seems to be wrong?

Answer 1

You should use double quotes here so that key can be evaluated
$_POST["pn$count"]
^ ^
You don't need to introduce $count variable. Change condition in for
You should prepare your query once and then execute it multiple times with different parameters. That's the whole point behind prepared statements. Preventing sql injections is just a beautiful side effect.
That being said your might look something like this
require("common.php");
$query = "INSERT INTO rmadb (rmanumber, parent, childpn, childsn, remarks, user, date) VALUES (:rmanumber, :parent, :childpn, :childsn, :remarks, :user, NOW())";
$stmt = $db->prepare($query);
for ($i = 1; $i <= $_POST['qty']; $i++) {
$query_params = array(
":rmanumber" => $_POST['rmanumber'],
":parent" => $_POST['parent'],
":childpn" => $_POST["pn$i"],
":childsn" => $_POST["sn$i"],
":remarks" => $_POST["rm$i"],
":user" => $_SESSION['user']['fname']." ".$_SESSION['user']['lname']
);
$res = $stmt->execute($query_params);
}

Answer 2

Anytime you see yourself naming inputs like rm1, rm2, etc. know that that this is a clear anti-pattern. You should be using array access notation for your input names like:
<input name="rm[]" ... />
PHP will automatically take all inputs with same name and compile into an array that is available in $_POST - so $POST['rm'] and so forth.
This would simplify you loop to something like
$count = $_POST['qty']; // not shown you probably want to validate this value before using it
for ($i = 0; $i < $count; $i++) {
$query_params = array(
":rmanumber" => $_POST['rmanumber'],
":parent" => $_POST['parent'],
":childpn" => $_POST['pn'][$i],
":childsn" => $_POST['sn'][$i],
":remarks" => $_POST['rm'][$i],
":user" => $_SESSION['user']['fname']." ".$_SESSION['user']['lname']
);
$res = $stmt->execute($query_params);
}
Note that since I am guessing you are using some kind of javascript in your form to create X number of input fields based on the value in qty, this saves you a lot of headache in javascript in trying to number each input field. You can easily just clone the same input field (or template for the input field) and insert it into the DOM X times without the need to individually change it's one's name property.