Function fetch() when I want to check [duplicate] - php

Question

This question already has answers here:
Why does this PDO statement silently fail?
(2 answers)
Closed 2 years ago.
I receive this error:
Fatal error: Call to a member function fetch() on boolean in
C:\xampp\htdocs\repo\generator\model\database.php on line 34
When I run this code:
class database
{
private $user = 'root';
private $pass = '';
public $pdo;
public function connect() {
try {
$this->pdo = new PDO('mysql:host=localhost; dbname=generatordatabase', $this->user, $this->pass);
echo 'Połączenie nawiązane!';
}
catch(PDOException $e) {
echo 'Połączenie nie mogło zostać utworzone: ' . $e->getMessage();
}
}
public function createTable() {
$q = $this->pdo -> query('SELECT * FROM article');
while($row = $q->fetch()) {
echo $row['id'].' ';
}
$q->closeCursor();
}
}
?>

Answer 1

As per the PHP manual for PDO::query
PDO::query() returns a PDOStatement object, or FALSE on failure.
It looks like your query is failing (on line 33) and thus returning a BOOLEAN (false), likely because at that point in execution, PDO has not connected to a database that contains a table called article. In the connect() method I see that it tries to connect to a db called 'generatordatabase'; ensure this connection is being made prior to calling createTable(), otherwise ensure that it contains a table called 'article'.
I would recommend adding some more code examples, for instance the code that calls this class/method before the error is triggered.

Answer 2

Some error handling will help you avoid issues like this:
$q = $this->pdo->query('SELECT * FROM article');
//error case
if(!$q)
{
die("Execute query error, because: ". print_r($this->pdo->errorInfo(),true) );
}
//success case
else{
//continue flow
}

Answer 3

I'm not sure wheatear this is exactly the error I struggled with, but my error was due to my $con variable, I used a single $con for 2 SQL statements, for example:
$con = new mysqli($host,$username,$password,$database);
$sql = "SELECT name FROM users WHERE email = '$email'";
$stm = $con->prepare($sql);
$stm->execute();
and
$sql1 = "INSERT INTO posts
VALUES('$email','$body')";
$stm1 = $con->prepare($sql1);
if ($stm1->execute()) {
I should have done:
$con = new mysqli($host,$username,$password,$database);
$sql = "SELECT name FROM users WHERE email = '$email'";
$stm = $con->prepare($sql);
$stm->execute();
and
$con1 = new mysqli($host,$username,$password,$database);
$sql1 = "INSERT INTO posts
VALUES('$email','$body')";
$stm1 = $con1->prepare($sql1);
$stm1->execute()