[RESOLVED] Fatal error: Call to a member function prepare() on a non-object

cluelessPHP

<?php	   

error_reporting(-1); // reports all errors
ini_set("display_errors", "1"); // shows all errors
ini_set("log_errors", 1);
ini_set("error_log", "php-error.log");


class Database
{
		public
		$connection,
		$host,
		$user,
		$password,
		$dataBase;

function __construct()
{
	$this->connection = false;
	$this->host = "localhost";
	$this->user = "root";
	$this->password = "";
	$this->dataBase = "soma";
	$this->connect();
}

function connect()
{
	if(!isset($this->connection))	//test for connection 
	{
			try 
			{
				$this->connection = new PDO("mysql:host=$this->host;dataBase=$this->dataBase", $this->user, $this->password);
			}
			catch (PDOException $e) 
			{
				echo $e->getMessage();
				die();
			}
	}
	if (!$this->connection) //if no connection end 
	{	
		function __destruct() 
		{
			 $this->connection = null;
		}
	}
	else
	{
		return $this->connection;
	}	
}	

}


class Username extends Database
	{
//basic test insert 
     public function insert() 
		{

		$test = $this->connection->prepare("INSERT INTO username (username) VALUES ('Yeaaap')");
		$test->execute();

	}
}

$tester = new Username(); 
$tester->insert();
var_export($test);

It "should be a database class which will extend so I can insert into it current error message

Fatal error: Call to a member function prepare() on a non-object in ... on line 64

Weedpacket

When [font=monospace]connect[/font] is first called, [font=monospace]$this->connection[/font] has already been set (to [font=monospace]false[/font], so the actual connection doesn't happen.

I suggest you replace [font=monospace]false[/font] in the constructor there with [font=monospace]null[/font]. A variable containing [font=monospace]null[/font] doesn't count as being set.

NogDog

The other option is to test for empty() instead of !isset() -- mainly a stylistic thing, though Weedpacket's suggestion might save a microsecond or two, since it only needs to check if it's set.

Derokorian

Weedpacket;11060241 wrote:
When [font=monospace]connect[/font] is first called, [font=monospace]$this->connection[/font] has already been set (to [font=monospace]false[/font], so the actual connection doesn't happen.

I suggest you replace [font=monospace]false[/font] in the constructor there with [font=monospace]null[/font]. A variable containing [font=monospace]null[/font] doesn't count as being set.

Or just don't assign it at all in the constructor, since an uninitialized variable (IE empty property) is already null, and the purpose of the connect is to set it anyway.

cluelessPHP

<?php	   

error_reporting(-1); // reports all errors
ini_set("display_errors", "1"); // shows all errors
ini_set("log_errors", 1);
ini_set("error_log", "php-error.log");


class Database 
	{

	protected 
	$host,
	$dbname,
	$user,
	$password,
	$db;

	function __construct($host = "",$dbname = "",$user = "",$password = "") 
	{
		$this->host = "localhost";
		$this->user = "root";
		$this->password = "";
		$this->dataBase = "soma";

		try 
		{
			$this->db = new PDO("mysql:host=$this->host;dbname=$this->dataBase", $this->user, $this->password);
		}
		catch (PDOException $e) 
		{
			echo $e->getMessage();
			die();
		}	

	}

	function testConnection()
	{

		if (!$this->db) //if no connection end 
		{	
			$this->db = true; 
		}
		else
		{
			function __destruct() 
			{
				return	$this->db = null;
				throw new Exception('DOH!!');
				return false; 					 
			}
		}	

	}

}


class Username extends Database
	{
//basic test insert 
     public function insert() 
		{	
			$test = $this->db->prepare("INSERT INTO username (username) VALUES ('Yeaaap')");
			$test->execute();
			echo "got it";
		}
	}

$tester = new Username(); 
$tester->insert();
//var_export($tester);

The problem with this, it allows me to insert but I veuagley suspect it's wrong

NogDog

A few things to consider...

You can simply(?) have your Database class extend PDO, adding a few tweaks to let you put your DB config within the class, if that's what you'd like to do.

class Database extends PDO
{
    private $host   = 'localhost';
    private $user   = 'root';
    private $pass   = '';
    private $dbname = 'soma';

    public function __construct($dsn = null, $user = null, $pass = null, $opts = null)
    {
        parent::__construct(
            "mysql:host={$this->host};dbname={$this->dbname}",
            $this->user,
            $this->pass,
            $opts
        );
        $this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }
}

Since Username is not a database thing, but something that uses a database thing (a.k.a. object), in this case I would not have it extend the Database class, but instead use it via composition, in this case passing an already created PDO object into the class's constructor.

class Username
{
    private $pdo;

    public function __construct(PDO $pdo)
    {
        $this->pdo = $pdo;
    }

    public function create($username)
    {
        $sql = "INSERT INTO username (username) VALUES (:username)";
        $stmt = $this->pdo->prepare($sql);
        $stmt->bindParam(':username', $username);
        $stmt->execute();
        return $stmt->rowCount();
    }
}

Then to use it:

$db = new Database();
$username = new Username($db);
$username->create('NogDog');

Note that since Database is a child of PDO, it counts as being a PDO-type object with regard to the type-hinting for Username's constructor.

cluelessPHP

class Database extends PDO

Oh I think I understand, PDO is a class in php so by extending it you're taking advantage of pre-existing erm...wrappers?/classes?

NogDog

cluelessPHP;11060271 wrote:
class Database extends PDO 
Oh I think I understand, PDO is a class in php so by extending it you're taking advantage of pre-existing erm...wrappers?/classes?

Yep. You could do the same sort of thing with the MySQLi class if you wanted to (I wouldn't 😉 ), but you could not do it with the old MySQL extension, since it was just a set of functions. So your new Database class becomes a specific implementation of the PDO class by extending it, inheriting all its methods and properties, then adding to those or overriding them as needed. On the other hand, a User is not a specific case of a database, so it doesn't make much sense to have it be a child of (extend) either PDO or its child Database class. It does, however, need access to the database, so by passing any PDO-type object into it via its constructor, you now have a sort of contract in place saying, "You can only use me if you give me a PDO object that I can use."

Derokorian

NogDog;11060275 wrote:
Yep. You could do the same sort of thing with the MySQLi class if you wanted to (I wouldn't 😉 ), but you could not do it with the old MySQL extension, since it was just a set of functions. So your new Database class becomes a specific implementation of the PDO class by extending it, inheriting all its methods and properties, then adding to those or overriding them as needed. On the other hand, a User is not a specific case of a database, so it doesn't make much sense to have it be a child of (extend) either PDO or its child Database class. It does, however, need access to the database, so by passing any PDO-type object into it via its constructor, you now have a sort of contract in place saying, "You can only use me if you give me a PDO object that I can use."

Another benefit of using the database class in the username class, is it becomes easier to change the database connection the class uses. Instead of changing the definition of the class, you can simply construct it with a different database object.

$db = new Database2(); // same class with different connection parameters
$username = new Username($db); 
$username->create('NogDog');

now You've saved to an entirely new connection without having to restructure your classes.

cluelessPHP

Makes sense, going to try work on something I have an idea for now it's quite outside and I can google things again

dalecosp

And the formal name for this concept is Inheritance.

cluelessPHP

dalecosp;11060299 wrote:
And the formal name for this concept is Inheritance.

Yep. sitting working with classes and functions more now, interacting with them properly is my main concern now

NogDog

I found the book "PHP 5 Objects, Patterns, and Practice", by Matt Zandstra, to be a big help to me when I was first trying to really understand OOP.

Derokorian

NogDog;11060317 wrote:
I found the book "PHP 5 Objects, Patterns, and Practice", by Matt Zandstra, to be a big help to me when I was first trying to really understand OOP.

cluelessPHP

<?php 

class ShopProduct
{
	public 
		$numPages,
		$playLength,
		$title,
		$producerMainName,
		$producerFirstName,
		$price;

	function __construct($title, $firstName, $mainName, $price, $numPages=0, $playLength=0)
	{
		$this->title = $title;
		$this->producerFirstName = $firstName;
		$this->producerMainName = $mainName;
		$this->price = $price;
		$this->numPages = $numPages;
		$this->playLength = $playLength;
	}

	function getProducer()
	{
	return 
		"{$this->producerFirstName} ".
		"{$this->producerMainName}";
	}

	function getSummaryLine()
	{
		$base = "$this->title ({$this->producerMainName},";
		$base .= "{$this->producerFirstName})";
		return $base;
	}	
}

class CdProduct extends ShopProduct
{
	function getPlayLength()
	{
		return $this->playLength;
	}

function getSummaryLine()
{
	$base = "{$this->title} ({$this->producerMainName},";
	$base .= "{$this->producerFirstName})";
	$base .= ": Playing time - {$this->playLength}";
	return $base;
}
}	
class BookProduct extends ShopProduct
{
	function getNumberOfPages()
	{
		return $this->numPages;
	}

function getSummaryLine()
{
	$base = "{$this->title} ({$this->producerFirstName},";
	$base .= "{$this->producerFirstName})";
	$base .= ": Page count - {$this->numPages}";
	return $base;
}
}

$product2 = new CdProduct("Exile on Coldharbour lane", "The " . "Alabama 3", 10.99, null, 60.33);
print "artist: {$product2->getProducer()}\n";
print "Summary: {$product2->getSummaryLine()}\n";

It's more a case of this I'm not quite sure about yet, sure I can print static stuff but I will need to be able to dynamically generate stuff too

$product2 = new CdProduct("Exile on Coldharbour lane", "The " . "Alabama 3", 10.99, null, 60.33);
print "artist: {$product2->getProducer()}\n";
print "Summary: {$product2->getSummaryLine()}\n";

NogDog

You could make a general method to get all the properties as an array (maybe using [man]get_object_vars[/man]?) so that the client code can pick and choose what it needs when it needs it.

Derokorian

I wouldn't put playlength in the shopproduct class because its not a constant property (like bookproduct doesn't use it). Instead it should only be part of the CDProduct Class, since this is the only one that uses it. To make the parent class more generic, you could initialize it instead of using a bunch of arguments to the constructor (which is generally bad design anyway) but instead with an array, like:

public function __construct(array $props) {
    foreach ($props as $name => $value) {
        if (property_exists($this, $name)) {
            $this->$name = $value;
        }
    }
}