mysql数据库错误：在null上调用成员函数query（）

Question

I am trying to create a mysql table using php

I have the following function to create the table

class dbActions{
public $connection;
function dbConnect(){
    $dbname = 'kilimokenya';
    $dbhost = 'localhost';
    $dbpass = '';
    $dbuser = 'root';

    $connection = new mysqli($dbhost, $dbuser, $dbpass, $dbname);

    if($connection ->connect_errno) echo ($connection ->connect_error());
}

function createCustomerTbl(){
    GLOBAL $connection;
    $CustomerTbl = "CREATE TABLE customers_tbl(
        customer_id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
        firstname VARCHAR(30) NOT NULL,
        lastname VARCHAR(30) NOT NULL,
        emailAddress VARCHAR(30) NOT NULL,
        phone_number VARCHAR(15) NOT NULL,
        dateRegistered TIMESTAMP
        )";
    $check = $connection ->query($CustomerTbl);
    if(!$check)
        echo "Customer table not created because ".$connection ->error;
    return true;
}

I call the function here :

$dbObject = new dbActions();
$dbObject ->dbconnect();

$dbObject ->createCustomerTbl();

I get the following error when i run the code: Fatal error: Call to a member function query() on null in C:\xampp\htdocs\current\kilimokenyafoods\common\server.php on line 31

What im i missing?

Answer 1

The $connection property should be accessed within the class using $this rather than declaring as a global variable.

The above could be rewritten a little to follow the singleton pattern to ensure that only one instance of the class is initialised for your scripts

class dbAction{

    private static $instance=false;
    private $connection;

    private function __construct($dbhost, $dbuser, $dbpass, $dbname){
        $this->connection=new mysqli($dbhost, $dbuser, $dbpass, $dbname);
    }
    public static function initialise($dbhost, $dbuser, $dbpass, $dbname){
        if( !self::$instance ) self::$instance=new dbAction( $dbhost, $dbuser, $dbpass, $dbname );
        return self::$instance;
    }


    public function createCustomerTbl(){
        $sql='CREATE TABLE customers_tbl(
            customer_id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
            firstname VARCHAR(30) NOT NULL,
            lastname VARCHAR(30) NOT NULL,
            emailAddress VARCHAR(30) NOT NULL,
            phone_number VARCHAR(15) NOT NULL,
            dateRegistered TIMESTAMP)';
        $res = $this->connection->query( $sql );
        if( !$res )printf( 'Customer table not created because : %s', $this->connection->error );
        return $res;
    }
}



$dbo=dbAction::initialise( 'localhost', 'root', 'xxx', 'kilimokenya' );
$status=$dbo->createCustomerTbl();

echo $status ? 'good' : 'bad';