PHP pdo lastInsertId() always returns a 0 - php

Question

Here is the database and PHP information:
Database vendor and version : 10.2.32-MariaDB
PHP Version : PHP 7.3
I am running into an issue when trying to retrieve the last inserted id to use in another insert statement using PHP PDO and MariaDB...
Sorry for the vague pseudo-code below but trying to mask proprietary data:
try {
include_once $pdo connection stuff here;
$pdo->beginTransaction();
$sql = 'AN INSERT STATEMENT HERE';
$stmt = $pdo->prepare($sql);
$stmt->bindValue(':some_value', $some_value);
$stmt->bindValue(':another_one', $another_one);
$stmt->bindValue(':additional_value', $additional_value);
$stmt->execute();
// have tried to call $pdo->commit(): here to no avail.
//should get the last inserted id here on the AUTO_INCREMENT column in the target table from above prepared statement
// the AI column is not included in the insert statement above nor any value specified in the VALUES clause so should
// set to the next available value (and does so according to peeking at row over in phpMyAdmin).
$last_insert_id = $pdo->lastInsertId();
// don't really want to commit the above insert here just yet in case something goes wrong below and can rollback
// a file could be uploaded but it's not mandatory
if (!empty($_FILES['some_file'])) { // file has been attached.
// some file operations here
// some file operations here
// some file operations here
// some file operations here
$extensions = array("extension I am expecting");
if (in_array($file_ext, $extensions) === false) {
//Uh-oh not the correct extension so rolling back
$pdo->rollback();
die('message here...');
} else {
// file type is ok so proceeding
// if the file already exists, get rid of it so we don't have 2 copies on the server
if (file_exists($file_dir.$file_name)) {
unlink($file_dir.$file_name);
}
// storing the attached file in designated directory
move_uploaded_file($file_tmp, $file_dir.$file_name);
// going to parse the file...
$xml = simplexml_load_file('xml file to parse');
// have tried to call $pdo->commit(): here to no avail.
foreach ($xml->children() as $row) {
foreach ($row as $obj) {
if (some checking things with the obj here yada yada yada) {
$insert_sql = "INSERT INTO another table(columns.....) //there is no AUTO_INCREMENT column attribute on any column in this table just FYI
VALUES(column values...)";
$stmt = $pdo->prepare($insert_sql);
// want the AI value here from the very first insert above but it's always zero (0)
$stmt->bindValue(':last_insert_id', intval($last_insert_id), PDO::PARAM_INT);
$stmt->bindValue(':some_column', strval($some_column));
$stmt->bindValue(':another_one', strval($another_one));
$stmt->execute();
}
}
}
// all is good so committing the first insert
$pdo->commit();
}
} else {
// the file was not uploaded and it is not mandatory so committing the first insert here and the second insert never happens
$pdo->commit();
}
} catch (Exception $e) {
if ($pdo->inTransaction()) {
$pdo->rollback();
}
throw $e;
echo 'An error occurred.';
echo 'Database Error '. $e->getMessage(). ' in '. $e->getFile().
': '. $e->getLine();
}
}
My goal is that the first insert always gets inserted (should nothing fail in it). The second insert is optional depending if a file is attached.
If the file is attached and all the file operations are good, then I'll insert some values in another table and use the auto_increment value from the first insert in this second table ( the idea is as a foreign key).
But for whatever reason, the value inserted is always zero (0).
When the code executes successfully both table inserts complete (granted a file is present and the second insert even fires)...
The row in the first table is created and 1 or more rows in the second insert's table are created but they have a value of 0 in the designated column, where I would expect them to contain the AI value from the first insert...
I've tried to call $pdo->commit() in several other places that "make sense" to me thinking that the first insert must be committed for an AI value to even exist on that table but no luck with any of them...
I even tried this I saw in another Stackoverflow post as a test to make sure PDO isn't doing anything wonky, but PDO is fine...
$conn = new PDO(connection info here);
$conn->exec('CREATE TABLE testIncrement ' .
'(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, name VARCHAR(50))');
$sth = $conn->prepare('INSERT INTO testIncrement (name) VALUES (:name)');
$sth->execute([':name' => 'foo']);
var_dump($conn->lastInsertId());
And the above does return: string(1) "1"
So I think PDO is ok (granted the above was not wrapped in a transaction and I haven't tried that yet)
Hope I have provided enough clear details...
Does anyone know why I am getting 0 and not the last insert id?
Any help is greatly appreciated and thank you!

Answer 1

You need to check the result of $stmt->execute. Read the docs on PDOStatement::execute and you'll see that it returns a boolean value:
Returns TRUE on success or FALSE on failure.
Then read the docs on PDOStatement::errorInfo. Check this if execute returns FALSE.
$stmt->execute();
echo "\nPDOStatement::errorInfo():\n";
$arr = $stmt->errorInfo();
print_r($arr);
EDIT: it's not generally a good idea to output errors to the screen, I did so in this case for convenience. A better approach would be to write a log file:
$arr = $stmt->errorInfo();
file_put_contents("/path/to/file.log", print_r($arr, TRUE));