How to save multiple values from same input names - php

Question

How would I save in multiple rows values from same input names.
For example, my php,html code from is:
<form action="functions.php" method="post" name="grades">
<table>
<thead>
<tr>
<th>Subject</th>
<th>Grade</th>
</tr>
</thead>
<tbody>
<?php $unos = $baza->odradi("SELECT subject FROM subjects ORDER BY id ASC");
if (!empty($unos)) {
foreach($unos as $row=>$value){ ?>
<tr>
<td><input type="hidden" name="subject_id[]" value="<?= $unos[$row]["id"]; ?>"> <?= $unos[$row]["subject"]; ?></td>
<td>
<select class="form-control input-xs" name="grade_id[]" required>
<option selected disabled>Select grade</option>
<option value="5">excelent</option>
<option value="4">very good</option>
<option value="3">good</option>
<option value="2">ok</option>
<option value="1">bad</option>
</select>
</td>
</tr>
</tbody>
</table>
<input type="submit" name="grades" class="btn btn-success btn-lg" value="Submit grades">
</form>
And function which from where it needs to be saved looks like this:
if (isset($_POST['grades'])) {
foreach (array_combine($_POST['subject_id'], $_POST['grade_id']) as $i => $val){
$subject = $_POST["subject_id"][$i];
$grade = $_POST["grade_id"][$i];
$sql = "INSERT INTO final_grade (subject_id,grade_id) VALUES ('$subject','$grade')";
$u = mysqli_query($db, $sql);
}
But it's all messed up,in first two rows there is no grade or subject saved, and all some rows are missing completely.

Answer 1

Because you are calling array_combine(), your loop is not passing the subarray indexes as $i anymore. It is passing the subject_id as $i and grade_id as $val. You could have just used $i and $val as the values to insert rather than trying to re-access the $_POST arrays with $i.
Cleaner scripting would be to use the ids as hardcoded element keys on each <select> instead of passing a hidden field.
<?php
$options = [
5 => 'excellent',
4 => 'very good',
3 => 'good',
2 => 'ok',
1 => 'bad'
];
?>
<td><?= $unos[$row]["subject"]; ?></td>
<td><select class="form-control input-xs" name="grade[<?= $unos[$row]["id"]; ?>]" required>
<option disabled>Select grade</option>
<?php
foreach ($options as $opt_id => $opt_val) {
echo "<option value=\"{$opt_id}\">{$opt_val}</option>";
}
?>
</select>
</td>
Then you can simply access the associative submission.
if (isset($_POST['grade'])) {
// use prepared statement and bind variables
foreach ($_POST['grade'] as $id => $val) {
// execute prepared statement with each iteration
}
}
Alternatively, you could build up a single batch of results and do a single INSERT (I'd probably do it this way).
Suggested batch insert code:
$placeholders = [];
$params = ['']; // instantiate with no types in first element
foreach ($_POST['grade'] as $subject_id => $grade_id) {
$placeholders[] = '(?,?)'; // all necessary placeholders for the row
$params[0] .= 'ii'; // because you are passing 2 integer values per batch
array_push($params, $subject_id, $grade_id);
}
// execute single batch of inserts
$query = "INSERT INTO final_grade (subject_id,grade_id) VALUES " . implode(',', $placeholders);
$stmt = $conn->prepare($query);
$stmt->bind_param($params);
$stmt->execute();
The truth is, there are a number of ways that you can pass the data from your form and a number of ways that you can execute the INSERT query. I won't bother to write out all of the variations -- do what you like ...but definitely write stable/secure queries.