lastInsertId() returns NULL - php

Question

i am trying to get the last id inserted in my sql query, but my varieble returns with NULL
here is my code
$conn->beginTransaction();
try{
$stmt=$conn->prepare("SELECT cn_id FROM food_category WHERE catname= :catname");
$stmt->bindParam(':catname', $_POST['catname'], PDO::PARAM_STR);
$stmt->execute();
$catres= $stmt->fetch(PDO::FETCH_ASSOC);
if(count($catres) > 0 ){
$cn_id= $catres['cn_id'];
}else{
$stmt1= $conn->prepare("INSERT INTO food_category (catname) VALUES (:catname)");
$stmt1->bindParam(':catname', $_POST['catname'], PDO::PARAM_STR);
$stmt1->execute();
$cn_id= $stmt1->lastInsertId();
}
$stmt2=$conn->prepare("SELECT cn_id FROM food_category_en WHERE catname= :catname_en");
$stmt2->bindParam(':catname_en', $_POST['catname_en'], PDO::PARAM_STR);
$stmt2->execute();
$catresen= $stmt2->fetch(PDO::FETCH_ASSOC);
if(count($catresen) > 0 ){
$cn_id_en= $catresen['cn_id'];
}else{
$stmt3= $conn->prepare("INSERT INTO food_category_en (catname) VALUES (:catname_en)");
$stmt3->bindParam(':catname_en', $_POST['catname_en'], PDO::PARAM_STR);
$stmt3->execute();
$cn_id_en= $stmt3->lastInsertId();
}
$stmt4=$conn->prepare("INSERT INTO food_category_main (st_id, cn_id, cn_id_en, catcount) VALUES (:st_id, :cn_id, :cn_id_en, :catcount)");
$stmt4->bindParam(':st_id', $_POST['st_id'], PDO::PARAM_INT);
$stmt4->bindParam(':cn_id', $cn_id, PDO::PARAM_INT);
$stmt4->bindParam(':cn_id_en', $cn_id_en, PDO::PARAM_INT);
$stmt4->bindParam(':catcount', $noc, PDO::PARAM_INT);
$stmt4->execute();
$stmt5=$conn->prepare("UPDATE magazia_main SET noc= :noc WHERE st_id= :st_id");
$stmt5->bindParam(':st_id', $_SESSION['st_id'], PDO::PARAM_INT);
$stmt5->bindParam(':noc', $noc, PDO::PARAM_INT);
$stmt5->execute();
$conn->commit();
header ("Location:dashboard.php?store=".$_SESSION['name']);
exit;
}catch(Exception $e){
//An exception has occured, which means that one of our database queries
//failed.
//Print out the error message.
echo $e->getMessage();
//Rollback the transaction.
$conn->rollBack();
}
I read in the php manual here that if am i using transaction the lastInsertId will return 0. As you see both lastInsertId (1st in stmt1, 2nd in stmt3) are before $conn->commit();, although they return with NULL.
cn_id in food_category and cn_id in food_category_en are both primary keys and AUTO_INCREMENT
i search for some solutions in the internet but none of them seems to fix my problem.
here is a printscreen from php my admin
*** connection to database****
$servername = "localhost";
$username = "root";
$password = "12345";
try {
$conn = new PDO("mysql:host=$servername;dbname=superdb; charset=utf8", $username, $password);
// set the PDO error mode to exception
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
catch(PDOException $e)
{
echo "Connection failed: " . $e->getMessage();
}
?>
Any ideas?
Thanks in advance
Vaggelis

Answer 1

After hours of searching, i didnt find the reason why lastInsertId() returns NULL. Anyway changed my code a little bit and now is working.
I removed the SELECT queries from transaction and i put them in the if statement which checks if the input has value. After that i made two if statements in the pdo transaction to check that if the value cn_id= 0 or cn_id_en= 0.
Here is my code now:
//check is inputs has value
if (empty($_POST['catname'])) {
$errors[] = 'Ξεχάσατε το όνομα της κατηγορίας!';
}else{
$stmt=$conn->prepare("SELECT cn_id FROM food_category WHERE catname= :catname");
$stmt->bindParam(':catname', $_POST['catname'], PDO::PARAM_STR);
$stmt->execute();
$catres= $stmt->fetch(PDO::FETCH_ASSOC);
if(count($catres) > 0 ){
$cn_id= $catres['cn_id'];
}else{
$cn_id=0;
}
}
if (empty($_POST['catname_en'])) {
$errors[] = 'Ξεχάσατε το όνομα της κατηγορίας στα Αγγλικά!';
}else{
$stmt2=$conn->prepare("SELECT cn_id FROM food_category_en WHERE catname= :catname_en");
$stmt2->bindParam(':catname_en', $_POST['catname_en'], PDO::PARAM_STR);
$stmt2->execute();
$catresen= $stmt2->fetch(PDO::FETCH_ASSOC);
if(count($catresen) > 0 ){
$cn_id_en= $catresen['cn_id'];
}else{
$cn_id_en=0;
}
}
if(empty($errors)){
//pdo trasaction
$conn->beginTransaction();
try{
if($cn_id == 0){
$stmt1= $conn->prepare("INSERT INTO food_category (catname) VALUES (:catname)");
$stmt1->bindParam(':catname', $_POST['catname'], PDO::PARAM_STR);
$stmt1->execute();
$cn_id= $conn->lastInsertId();
echo "id1=" . $cn_id;
}
if($cn_id_en == 0){
$stmt3= $conn->prepare("INSERT INTO food_category_en (catname) VALUES (:catname_en)");
$stmt3->bindParam(':catname_en', $_POST['catname_en'], PDO::PARAM_STR);
$stmt3->execute();
$cn_id_en= $conn->lastInsertId();
}
$stmt4=$conn->prepare("INSERT INTO food_category_main (st_id, cn_id, cn_id_en, catcount) VALUES (:st_id, :cn_id, :cn_id_en, :catcount)");
$stmt4->bindParam(':st_id', $_POST['st_id'], PDO::PARAM_INT);
$stmt4->bindParam(':cn_id', $cn_id, PDO::PARAM_INT);
$stmt4->bindParam(':cn_id_en', $cn_id_en, PDO::PARAM_INT);
$stmt4->bindParam(':catcount', $noc, PDO::PARAM_INT);
$stmt4->execute();
$stmt5=$conn->prepare("UPDATE magazia_main SET noc= :noc WHERE st_id= :st_id");
$stmt5->bindParam(':st_id', $_SESSION['st_id'], PDO::PARAM_INT);
$stmt5->bindParam(':noc', $noc, PDO::PARAM_INT);
$stmt5->execute();
$conn->commit();
header ("Location:dashboard.php?store=".$_SESSION['name']);
exit;
}catch(Exception $e){
//An exception has occured, which means that one of our database queries
//failed.
//Print out the error message.
echo $e->getMessage();
//Rollback the transaction.
$conn->rollBack();
}
i wont accept this as an answer for few days, in order to be seen from as many users is possible

Answer 2

Please replace $stmt1, $stmt3 with $conn your code is like this
$conn->beginTransaction();
try{
$stmt=$conn->prepare("SELECT cn_id FROM food_category WHERE catname= :catname");
$stmt->bindParam(':catname', $_POST['catname'], PDO::PARAM_STR);
$stmt->execute();
$catres= $stmt->fetch(PDO::FETCH_ASSOC);
if(count($catres) > 0 ){
$cn_id= $catres['cn_id'];
}else{
$stmt1= $conn->prepare("INSERT INTO food_category (catname) VALUES (:catname)");
$stmt1->bindParam(':catname', $_POST['catname'], PDO::PARAM_STR);
$stmt1->execute();
$cn_id= $conn->lastInsertId();
}
$stmt2=$conn->prepare("SELECT cn_id FROM food_category_en WHERE catname= :catname_en");
$stmt2->bindParam(':catname_en', $_POST['catname_en'], PDO::PARAM_STR);
$stmt2->execute();
$catresen= $stmt2->fetch(PDO::FETCH_ASSOC);
if(count($catresen) > 0 ){
$cn_id_en= $catresen['cn_id'];
}else{
$stmt3= $conn->prepare("INSERT INTO food_category_en (catname) VALUES (:catname_en)");
$stmt3->bindParam(':catname_en', $_POST['catname_en'], PDO::PARAM_STR);
$stmt3->execute();
$cn_id_en= $conn->lastInsertId();
}
$stmt4=$conn->prepare("INSERT INTO food_category_main (st_id, cn_id, cn_id_en, catcount) VALUES (:st_id, :cn_id, :cn_id_en, :catcount)");
$stmt4->bindParam(':st_id', $_POST['st_id'], PDO::PARAM_INT);
$stmt4->bindParam(':cn_id', $cn_id, PDO::PARAM_INT);
$stmt4->bindParam(':cn_id_en', $cn_id_en, PDO::PARAM_INT);
$stmt4->bindParam(':catcount', $noc, PDO::PARAM_INT);
$stmt4->execute();
$stmt5=$conn->prepare("UPDATE magazia_main SET noc= :noc WHERE st_id= :st_id");
$stmt5->bindParam(':st_id', $_SESSION['st_id'], PDO::PARAM_INT);
$stmt5->bindParam(':noc', $noc, PDO::PARAM_INT);
$stmt5->execute();
$conn->commit();
header ("Location:dashboard.php?store=".$_SESSION['name']);
exit;
}catch(Exception $e){
//An exception has occured, which means that one of our database queries
//failed.
//Print out the error message.
echo $e->getMessage();
//Rollback the transaction.
$conn->rollBack();
}
If you get by SQL query then
$stmt1 = $db->query("SELECT LAST_INSERT_ID()");
$lastId = $stmt1->fetchColumn();