Simple PHP OOP Query null

Question

I am trying to write a simple program that queries sql to the database using object orientated programing. I keep getting the error:

Fatal error: Uncaught Error: Call to a member function query() on null in C:\xampp\htdocs\learning\core\classes\core.php:11 Stack trace: #0 C:\xampp\htdocs\learning\core\classes\core.php(23): core->query('SELECT * FROM c...') #1 C:\xampp\htdocs\learning\core\classes\core.php(27): test->test() #2 C:\xampp\htdocs\learning\core\init.php(6): require('C:\xampp\htdocs...') #3 {main} thrown in C:\xampp\htdocs\learning\core\classes\core.php on line 11

<?php
class core{
    protected $db, $results;
    private $rows;

    public function __construct(){
        $this->db = new mysqli('localhost', 'root','','test');
    }

    public function query($sql){
        $this->result = $this->db->query($sql);
    }

    public function rows(){
        for($x = 1; $x <= $this->db->affected_rows; $x++){
            $this->rows[] = $this->result->fetch_assoc();
        }
        return $this->rows;
    }
}
class test extends core{
    public function test(){
        $this->query("SELECT * FROM currentseason");

    }
}


  $test = new test();
    $test->test();
    ?>

It would seem that `$this->db` is `NULL`, you should be checking the result of `$this->db = new mysqli('localhost', 'root','','test')` to make sure it succeeded. — Nick, Oct 16 '18 at 00:47
The real issue here is that without a `__construct()` method, PHP will also use a method named the same as the class as the constructor so unfortunately OP, `test#test()` is your constructor. I'd say this little fact is not widely known (these days) so downvotes are a little harsh. — Phil, Oct 16 '18 at 02:36
@Nick that's not necessary if OP has [set MySQLi to throw exceptions](https://stackoverflow.com/a/22662582/283366) (which is always a good idea IMO) — Phil, Oct 16 '18 at 02:39
@Phil definitely a good idea but seemingly one that has been adopted more by the PDO crowd... — Nick, Oct 16 '18 at 03:09
The problem was that the method name "test" was the same name as the class. Thank you for your help! — Temp0w, Oct 16 '18 at 14:10

Paul T. · Accepted Answer · 2018-10-16T02:37:59.647

You have not called the parent constructor from the test class.

The PHP docs says:

Note: Parent constructors are not called implicitly if the child class defines a constructor. In order to run a parent constructor, a call to parent::__construct() within the child constructor is required. If the child does not define a constructor > then it may be inherited from the parent class just like a normal class method (if it was not declared as private).

I modified your test class as follows: (with a modified query to a table in my test DB)

class test extends core {
    public function __construct(){
        parent::__construct();
    }

    public function test() {
        $this->query("SELECT * FROM bug_table");
        foreach ($this->rows() as $row) {
            echo $row['category_id'], '<br>';
        }
    }
}

Output:

Server
Database
Server
Server
Server

...at the same PHP information found here, I changed the test() class constructor to __construct as you have in the core class, but kept the function named test() that runs the query. Having a constructor the same name as the class is quickly being deprecated. Depending on your PHP version, run php -l file.php at the command line on your file to check any potential issues.

The problem was the method name "test" was the same name as the class. Thank you for your help! — Temp0w, Oct 16 '18 at 14:11

Simple PHP OOP Query null

1 Answers1