mcbeav mcbeav - 3 months ago 9
PHP Question

Call to a member function prepare() on a non-object PHP Help

I am trying to write a PHP function. It is very simple. It is just a prepared statement that queries the database, but I can not get this to work. I keep recieving the error Call to a member function prepare() on a non-object. here is the code:

$DBH = new mysqli("host", "test", "123456", "dbname");
function selectInfo($limit, $offset){
$stmt = $DBH->prepare("SELECT * FROM information LIMIT ?,?");
$stmt->bind_param("ii", $limit, $offset);
$stmt->execute();
}
selectInfo();


Any time I call the function i get that error. Can someone please help?

Answer

It's a scoping error. You're making $DBH a global variable. So when you enter the function, the global variable is not available. You have 5 real options.

1. Use the global keyword

function doSomething() {
    global $DBH;
    //...

This is not a good idea, since it makes maintenance and testing a PITA. Imagine trying to debug that function call. You now need to go find out where $DBH is defined to try to figure out what's going on...

2. Make $DBH a parameter to the function

function doSomething(MySQLi $DBH) {

It has the advantage of being explicit. But it's still not great since the calling code then needs to keep track of the global variable.

3. Create a function to "get" the $DBH object

function getDBH() {
    static $DBH = null;
    if (is_null($DBH)) {
        $DBH = new mysqli(...);
    }
    return $DBH;
}

function doSomething() {
    $DBH = getDBH();
}

This has the advantage of getting around the global variable problem completely. But it's also hard to have multiple connections or re-use any of the code for other connections.

4. Create a class to wrap database access

class Database {
    public function __construct($host, $user, $pass) {
        $this->DBH = new MySQli($host, $user, $pass);
    }
    public function doSOmething() {
        $this->DBH->foo();
    }
}

This encapsulates everything for you. All database access will go through a single class, so you don't need to worry about global variable access or anything else.

5. Use a pre-built class/framework

This is the best option, since you don't need to worry about doing it yourself.

Database Access Classes:

Full Frameworks:

Really, the choices are endless. Find something you like, and stick with it. It really will make your life easier...

Good Luck!

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