未捕获错误：调用成员函数prepare（）on null error [duplicate]

Question

This question already has an answer here:

• Fatal error Call to a member function prepare() on null 1 answer

I know there were a lot of answers related to this error, but I still don't know how to solve it... I'm trying to make the database connection, which would connect to the database and insert user's entered values in it and i got this error. I've created 2 files (with different classes):

Here is a connection file:

<?php
class Connection {
    // Setting Database Source Name (DSN)
 public function __construct() {
$dsn = 'mysql:host=localhost;dbname=employees';
// Setting options
$options = array (PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION);
// Making the connection to the database
try {
$this->dbh = new PDO($dsn, 'root', '', $options); 
}
catch (PDOException $e) {
$this->error = $e->getMessage();
        }
    }
}
$connection = new connection();
?>

And here is users.php file:

<?php
include 'connection.php';
class Users {
public $name;
public $surname;
public $employmentDate;
public function __construct()
{
if(isset($_POST['Submit'])) {
$this->name = $_POST['name'];
$this->surname = $_POST['surname'];
$this->employmentDate = $_POST['employmentDate'];
}
}
// Inserting users values to the database table
public function insertUserValues() {
 $stmt= 'INSERT INTO employee (name,surname,employment_date) VALUES (:name,:surname,:employmentDate)';
 $stmt = $this->dbh->prepare();
 $stmt->bindValue(':name',$name, PDO::PARAM_STR);
 $stmt->bindValue(':surname',$surname, PDO::PARAM_STR);
 $stmt->bindValue(':employmenDate',$employmentDate, PDO::PARAM_STR);
 $stmt->execute([$this->name,$this->surname,$this->employmentDate]);
}
}
$users = new Users();
$users->insertUserValues();
?>

I guess there are some mistakes in code structure, but I'm just learning, so. The code line which throws the error 18 line in users.php file:

$stmt = $this->dbh->prepare();

Please someone tell me where I am doing a mistake, thank you for any help.

</div>

Answer 1

You just have somes mistakes in your code. Try to use this lines :

Connection file :

<?php
class Connection {
    public $dbh;

    // Setting Database Source Name (DSN)
    public function __construct() {
        $dsn = 'mysql:host=localhost;dbname=employees';
        // Setting options
        $options = array (PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION);
        // Making the connection to the database
        try {
            $this->dbh = new PDO($dsn, 'root', '', $options); 
        }
        catch (PDOException $e) {
            $this->error = $e->getMessage();
        }
    }
}

$connection = new connection();

users.php file :

<?php

include 'connection.php';
class Users {
    public $name;
    public $surname;
    public $employmentDate;
    public $connection;

    public function __construct($connection)
    {
        $this->connection = $connection;
        if(isset($_POST['Submit'])) {
            $this->name = $_POST['name'];
            $this->surname = $_POST['surname'];
            $this->employmentDate = $_POST['employmentDate'];
        }
    }

    // Inserting users values to the database table
    public function insertUserValues() {
        $query = 'INSERT INTO employee (name,surname,employment_date) VALUES (:name,:surname,:employmentDate)';
        $stmt = $this->connection->dbh->prepare($query);
        $stmt->bindValue(':name',$this->name, PDO::PARAM_STR);
        $stmt->bindValue(':surname',$this->surname, PDO::PARAM_STR);
        $stmt->bindValue(':employmentDate',$this->employmentDate, PDO::PARAM_STR);
        $stmt->execute();
    }
}   

$users = new Users($connection);
$users->insertUserValues();

Explanations :

• You have to pass the $connection variable to your users class (or import it with global $connection;)
• Your connection file has to make visible the dbh property, otherwise you will not be able to make any query on your database
• PDO prepare() method is waiting for a query in first argument
• You don't need to pass an array to execute() method if you already have binded your values before