PHP/MySQL - How to delete insert if query fails? - php

Question

I have this code
<?php
class Objekt{
// database connection and table name
private $conn;
private $table_name = "objects";
// object properties
public $id;
public $id_group;
public $title;
public $description;
public $lat;
public $lng;
public $icon;
public $tagsraw;
// constructor with $db as database connection
public function __construct($db){
$this->conn = $db;
}
function create(){
// query to insert record
$query = "INSERT INTO
" . $this->table_name . "
SET
id_group=:id_group, title=:title, description=:description, lat=:lat, lng=:lng, icon=:icon;
SELECT max(id) AS id FROM objects;";
// prepare query
$stmt = $this->conn->prepare($query);
// sanitize
$this->id_group=htmlspecialchars(strip_tags($this->id_group));
$this->title=htmlspecialchars(strip_tags($this->title));
$this->description=htmlspecialchars(strip_tags($this->description));
$this->lat=htmlspecialchars(strip_tags($this->lat));
$this->lng=htmlspecialchars(strip_tags($this->lng));
$this->icon=htmlspecialchars(strip_tags($this->icon));
// bind values
$stmt->bindParam(":id_group", $this->id_group);
$stmt->bindParam(":title", $this->title);
$stmt->bindParam(":description", $this->description);
$stmt->bindParam(":lat", $this->lat);
$stmt->bindParam(":lng", $this->lng);
$stmt->bindParam(":icon", $this->icon);
// execute query
if($stmt->execute()){
//$stmt->execute();
/*
ERROR below here
Uncaught PDOException: SQLSTATE[HY000]: General error
stack trace:
#0 PDOStatement ->fetch(2)
#1 Objekt->create()
*/
$result = $stmt->fetch(PDO::FETCH_ASSOC);
$this->id = $result['id'];
echo "$this->id";
//get tags matches
$tags = [];
$this->tagsraw = preg_replace('/\s+/', '', $this->tagsraw);
$tags = explode(',', $this->tagsraw);
$id_tags = [];
for ($i = 0; $i < sizeof($tags); $i++) {
$query = "SELECT id FROM category WHERE title=" . tags[i];
$stmt = $this->conn->prepare($query);
$stmt->execute();
$result = $stmt->fetch(PDO::FETCH_OBJ);
$id_tags[i] = $result->id;
}
for ($i = 0; $i < sizeof($id_tags); $i++) {
$query = "INSERT INTO category_object SET id_object=" . $this->id . ", id_category=" . $id_tags[i];
$stmt = $this->conn->prepare($query);
$stmt->execute();
}
return true;
}
return false;
}
What I want to do:
Insert Object and create a relation to a category_object table over foreign keys id_object / id_category
What I would like to improve:
What do I have to do to delete an insert if it fails (where should I put a try/catch or something else)
What is wrong with my fetch? I Select the value from max(id) to get the value of my inserted object, why is it throwing an Exception
I have another Warning why is it telling me that
for ($i = 0; $i < sizeof($id_tags); $i++) {
$query = "INSERT INTO category_object SET id_object=" . $this->id . ", id_category=" . $id_tags[i];
$stmt = $this->conn->prepare($query);
$stmt->execute();
}
will be deprecated in future php versions..

Answer 1

Use transactions.
Any insert/update/delete done within a transaction will not be actually executed against the database until you call commit(), and you can always roll back the changes, abandoning them in case of failure.
In your code, you should be OK with replacing if($stmt->execute()){ with
try {
$this->conn->beginTransaction();
$stmt->execute();
// ...everything else from inside the if statement here...
$this->conn->commit();
return true;
} catch (\Exception $e) {
$this->conn->rollback();
return false;
}