I've 3 class (Mysqliconn, Users and News).
Mysqliconn.class
Class Mysqliconn {
..connect to db
}
News.class
class News {
private $db;
public function __construct( Mysqliconn $db ) {
$this->db = $db;
}
public test() {
do something...
}
}
Users.class
class Users {
private $db;
public function __construct( Mysqliconn $db ) {
$this->db = $db;
}
public test2() {
do something...
}
}
In my php page
$db = new Mysqliconn();
$nw = new News( $db );
$us = new Users( $db )
$us->test2();
$nw->test();
My error
Catchable fatal error: Argument 1
passed to Users::__construct() must be an instance of Mysqliconn,
none given, called in ....\class\class.news.php
Now in my class Users I would like to to call a News class method,
but I get an error if I try to istantiate the class News inside class Users.
How can I do this?
Thanks.
Plz post what error you are getting. Otherwise it's difficult to capture the problem. But if you dont want to instantiate the news class in the user class you can access it like
class News
{
// news class
}
class Users
{
public function some_method(News $news){
// work with the $news object
}
}
$us = new Users();
$us->some_method(new News(/*$db*/));
This is just a basic code to give you an idea of how you can use it. In a production environment you have to take a lot of precautions.
Related
I'm trying to use an existing class which has my DB connection in it to make a call within a new class. Here is my code to do this:
class ajaxHandler {
protected static $db;
function __construct() {
if (!class_exists('Db')) {
include "db_class.php";
$db = new Db();
}
}
function show_contest_details ($contest_id){
echo "The contest id is: ".$contest_id;
$event__conetest_details = $db->select("SELECT * FROM FF_CREATE_EVENT");
} // end of show_contest_details function
}
I am getting the following errors:
Notice: Undefined variable: db in /var/www/ajax_class.php on line 18
Fatal error: Call to a member function select() on a non-object in /var/www/ajax_class.php on line 18
How can I use my DB class within this class?
You've forgotten about self:::
class ajaxHandler {
protected static $db;
function __construct() {
if (!class_exists('Db')) {
include "db_class.php";
}
self::$db = new Db();
}
function show_contest_details ($contest_id){
echo "The contest id is: ".$contest_id;
$event__conetest_details = self::$db->select("SELECT * FROM FF_CREATE_EVENT");
} // end of show_contest_details function
}
Second thing, it is better to move code creating instance of Db outside the conditional block. You may accidentally include Db in other place, and then ajaxHandler will stop working, and you will not understand easily why.
You use class_exists() to test whether or not you have created the database. That is not correct. class_exists() checks if the class has been defined, which is true after PHP has loaded the file, not after it has created the first instatiation of the class. What you need is this:
class ajaxHandler {
protected static $db;
function __construct() {
if (is_null(self::$db)) {
include "db_class.php";
self::$db = new Db();
}
}
}
Here is sample code:
namespace myApp
class app
{
private $pdo = null;
public function __construct() {
$this->user=new User();
$this->user->getPDO();
}
}
class User
{
public function getPDO() {
//get PDO from app class
}
}
How from User class get $pdo from app class??
Can't use extends because of construct in app class.
I don't want to declare independent classes (app and User) and than use global to communicate with each other.
EDIT:
is this solution ok?
namespace myApp
class app
{
public $pdo = null;
public function __construct() {
$this->user=new User($this);
$this->user->getPDO();
}
}
class User
{
private $app=null;
public function __construct($app) {
$this->app=$app;
}
public function getPDO() {
return $this->app->pdo;
}
}
This sounds like a good candidate for dependency injection.
You can declare the constructor for your Userclass for example like
__constuct($pdo) {
$this->pdo = $pdo;
}
And then create User like
$this->user = new User($this->pdo)
An added advantage of this is that when you want to test your code you can easily mock pdo and test user without doing actual database actions.
You have to declare 2 functions in your app class like this:
Then you have acces through this functions to the pdo variable
public function setPDO($pdo) {
$this->pdo = $pdo;
}
public function getPDO() {
return $this->pdo;
}
I'm trying to learn how to properly code PHP OOP.
This is where I'm running into issues.
I created several classes that extend main Application class and I want to make things work properly.
I have main file that's index.php that looks like this:
include_once('classes/Application.php');
include_once('classes/Configuration.php');
include_once('classes/Database.php');
$app = new Application;
$config = new Configuration;
$db = new Database;
var_dump($app->db_connected);
var_dump($db->db_connected);
$db->connect($config->dbhost, $config->dbuser, $config->dbpass, $config->dbname);
var_dump($app->db_connected);
var_dump($db->db_connected);
The output is:
1. bool(false)
2. bool(false)
3. bool(false)
4. bool(true)
My main application file looks like this:
class Application {
public $db_connected = false;
}
And my Database class looks like this:
class Database extends Application {
function connect($dbhost, $dbuser, $dbpass, $dbname) {
if(!$this->db_connected) {
mysql_connect($dbhost, $dbuser, $dbpass) or die(mysql_error());
mysql_select_db($dbname) or die(mysql_error());
$this->db_connected = true;
}
}
}
So the question is, why would line #3 of the output of index.php display false? The db_connected property has been overridden in Database class and set to TRUE, but it still returns false.
Although when accessed directly from Database class instance it shows TRUE correctly. What's the deal here?
Also when does the class EXTEND command occurs? Whenever parent class' instance is created or I have to manually create instance of the child class?
It seems you are reaching for the concept of of a static variable all instances of a class share the same static variable so using the new twice will not be an issue.
You can see the code on ideaone.
// your code goes here
class Application {
static $db_connected = false;
}
class Database extends Application {
function connect() {
if(!static::$db_connected) {
static::$db_connected = true;
}
}
}
$app = new Application;
$db = new Database;
var_dump(Application::$db_connected);
var_dump(Database::$db_connected);
$db->connect();
var_dump(Application::$db_connected);
var_dump(Database::$db_connected);
Your comment make me think you are looking for a better pattern all together. I would like to throw out some key principles namely OCP and LSP SOLID.
In this case you would avoid having Application being an instance of Database but instead use dependency injection. Here is the refactored code.
class Database {
private $db_connect = false;
public function connect () {
if(!$this->db_connect) { /* do connection */ }
}
}
class Application {
private $db;
public function setDatabse(Database $db) {
$this->db = $db;
}
public function getDatabase() {
return $this->db;
}
}
$db = new Database;
$app = new Application;
$app->setDatabase($db);
$app->getDatabase()->connect();
This line is your hint
Although when accessed directly from Database class instance it shows TRUE correctly. What's the deal here?
You have 2 instances. Above you are checking $db instance which you connected with, and then you print from $app which was never connected. They are separate entities, one is connected one is not.
Extend occurs as soon as the file is loaded, read by the php interpreter, this happens regardless of ever using the class.
Extend is called from the child and inherits everything form the class it extends. So if you call a child method in the parent, well you are doing it backwards. It goes one way, Prent -> Child.
I would use Dependance injection for the database, then you can reuse it's code.
Like this:
//parent class
class Application {
//holds a reference to the Database class
protected static $db_conn = false;
public function __construct($db){
self::$db_conn = $db;
}
}
//child class of Application
class Application2 extends Application {
public function getSomething($id){
return self::$db_conn->getbyId($id) ;
}
}
//separate utility class
class Database{
static $conn;
public function __construct( $dbhost, $dbname, $dbuser, $dbpass, $dbname) {
static::$conn = mysqli_connect($dbhost, $dbuser,$dbpass,$dbname);
}
public function getbyId( $id ){
..code to get stuff by id using $conn - previous connection ...
return $result;
}
}
$db = new Database("myhost", "myuser", "mypassw", "mybd");
$app = new Application2( $db );
$app->getSomething(1);
//create another app with the same database connection, this is the value of injecting it.
$second_app = new Application2( $db );
See you can reuse database over and over, you can replace it without changing the code in Application as long as the calls for the functions of the Database class don't change. Each thing is responsible for it's own business.
This is called separation of concerns.
Inheritance is good, when it's needed. You might have an basic application for free users of you're services and then extend that with a premium application for paid members. Sense they paid they get all the free functionality, but also the premium stuff to.
In my example above the database is something they both need, as well as other things will probably use this. Such as a login system may need a database connection, payment system might, a shopping cart might. These are all separate objects, they don't / nor should they extend off of one Master Class, that's a bad idea. Keep them separate.
STATIC
I seen mention of the :: static object operator. My example is a bit flawed when using the static property protected static $db_conn = false;
$app = new Application2( $db );
$second_app = new Application2( $db ); //assigning db 2x is not needed.
The reason for :: and the -> normal way. Is that static :: is shared across all instance of a class, and -> is just this instance of the class. I had assigned the $db class to a static variable 2 times a better way would have been like this.
//parent class
class Application {
protected static $db_conn = false;
//separate method then construct.
public function connect($db){
self::$db_conn = $db;
}
}
//we'll keep the rest of the code the same here.
$db = new Database();
$app = new Application2();
$app->connect( $db );
$second_app = new Application2();
$second_app->getSomething(1);
Now in this example $second_app never ran it's connect method. But because the first $app did and because the static for the database variable protected static $db_conn. Now all classes that have extended the Application class have a database connection. This is what static does. It's value is shared across all instance of the class. So when you see :: think all class instance and when you see -> think only this class instance. It's actually one thing I love about php, makes it so much easier to keep track of then in some other languages.
Not to confuse you but the other use of the :: is not actually needing an instance at all. Assume you have a Config class like this.
class Config{
static $db = 'hello';
static $items = array('one' => 'item 1' );
private __construct(){} // no construction allowed
static function getItem( $which ){
return self::$items[$which];
}
}
Now without ever creating an instance of the class by calling new Config() , you can simply.
echo Config::$db;
// prints hello
echo Config::getItem('one');
// prints 'item 1'
This is quite use full for config type classes. Where they are an empty shell just used to store data in and you don't need an object for them, essentially a way to keep things organized. So tying this in to the previous examples
$db = new Database(Config::$myhost, Config::$myuser, Config::$mypassw, Config::$mybd);
In your case best OOP practice is to use Mediator pattern. Concrete Mediator will be Application class:
class ApplicationBase {
private $db;
private $cfg;
public function setDb(Database $db) {
$this->db = $db; return $this;
}
public function setConfig(Config $cfg) {
$this->cfg = $cfg; return $this;
}
}
class Application extends ApplicationBase {
public function getDsn() {
return $this->cfg->getDsn();
}
public function getDbUser() {
return $this->cfg->getDbUser();
}
public function getDbPass() {
return $this->cfg->getDbPass();
}
public function getConnection() {
return $this->db->getConnection();
}
}
class AppComponent {
protected $app;
public function __construct(Application $app) {
$this->app = $app;
}
}
class Config extends AppComponent {
private $dsn;
private $dbuser;
private $dbpass;
// ... getters and setters
}
class Database extends AppComponent {
private $connection;
private function connect() {
$this->connection = new PDO(
$this->app->getDsn(),
$this->app->getUser(),
$this->app->getPass()
);
}
public function getConnection() {
if (null === $this->connection) $this->connect();
return $this->connection;
}
}
class Model extends AppComponent {
protected $table;
// Model stuff here
}
class Content extends Model {
public function getNews() {
$db = $this->app->getConnection();
return $db->query("SELECT * FROM $this->table LIMIT 5")->fetchAll();
}
}
Such architecture will be enough for simple, clean-looking applications and classes will be ready for easy unit-testing:
$app = new Application();
$cfg = new Config($app);
$db = new Database($app);
$app->setDb($db)->setConfig($cfg);
$content = new Content($app);
$news = $content->getNews();
My question is rather simple and after checking a few bits and bobs on here I feel its best to ask a new question.
Lets say I have 2 classes
class FirstClass {
function test() {
return "info";
}
}
class SecondClass {
function test() {
return "info";
}
}
Then I have my mysqli object
$mysqli = new mysqli(host, user, password, db);
What do i need to do to be able to use the mysqli object inside the functions inside the classes.
This is my 2 thoughts so far although I haven't placed it on a site for testing yet.
class FirstClass {
global $mysqli;
function test() {
$mysqli->query("some query");
return "info";
}
}
or
class FirstClass {
function test() {
global $mysqli;
$mysqli->query("some query");
return "info";
}
}
I am pretty sure I can setup a construct if need be but I just need to know which way is the best way/only way to share the mysqli object.
Thanks
EDIT:
So I have done a hell of a load of learning and now have a lot more experience with passing info in and out.
Here is a latest working example type that I use.
namespace Page;
use mysqli;
class edit extends details{
protected $db;
//this function is actually in the details class but there is no point in demoing 2 classes
function __construct(mysqli $con){
$this->db = $con;
}
}
To expand what Kneel told you in comments and to counter the other answer
class foo {
function __construct($mysqli){
$this->mysqli = $mysqli;
}
function test() {
return $this->mysqli->query("some query");
}
}
is what it have to be.
You should create a mysqli instance somewhere outside the class and then pass it in coustructor.
You could use __construct() to initialize your MYSQLi. You can then access it around your class with $this.
class FirstClass {
public function __construct(){
$this->mysqli = new mysqli("host", "user", "password", "db");
}
function test() {
$this->mysqli->query("some query");
return "info";
}
}
If you wanted to use it in your second class too, you could construct it in the same way or extend your first class.
class SecondClass extends FirstClass {
public function __construct(){
parent::__construct();
}
function test() {
return "info";
}
}
I have an issue accessing top level variables from sub-level class.
Here's an example...
Application.php:
class Application {
var $config;
var $db;
function __construct() {
include_once('Configuration.php');
include_once('Database.php');
$this->config = new Configuration;
$this->db = new Database;
}
}
Configuration.php:
class Configuration {
var $dbhost = 'localhost';
}
Database.php:
class Database {
function __construct() {
echo parent::config->dbhost;
}
}
It is clear to me that usage of parent is wrong here as the subclass does not extend the parent class, but how do I access it?
Thank you.
You should create a Base class that in its construct creates a $db link. Then let all classes that require database access extend that class. Your nomenclature here with "parent class" is incorrect.
class Base {
private $db; // Make it read-only
function __construct() {
$this->db = DB::connect(); // It's a good practice making this method static
}
function __get($property) {
return $this->$property;
}
}
class Application {
public $config;
function __construct() {
parent::__construct();
require_once 'Configuration.php';
require_once 'Database.php';
$this->config = new Configuration();
}
function random_function() {
$this->db(....) // Has full access to the $db link
}
}
The parent notation is used to access the parent of the object in the object hierarchy. What you are doing here is trying to get at the caller, not the parent
The way that you would do this is to pass in an instance of your configuration to the database object.
class Database {
protected $config;
public function __construct(Configuration $config){
$this->config = $config;
}
public function connect(){
//use properties like $this->config->username to establish your connection.
}
}
The parent notation is used when you extend a class and make a child class to call methods on the parent .
class MySuperCoolDatabase extends Database {
protected $is_awesome;
public function __construct(Configuration $config){
// do all the normal database config stuff
parent::__construct($config);
// make it awesome
$this->is_awesome = true;
}
}
This defines a child class, which is a type definition that serves the same role as the base class with a slightly different implementation. Instances of this can still be said to be a Database.... just a different kinds of database.
Well, although I think that Orangepills answer is better. If you dont want to use it and since all variables are public, you could simply pass the variable like this:
class Application {
var $config;
var $db;
function __construct() {
include_once('Configuration.php');
include_once('Database.php');
$this->config = new Configuration;
$this->db = new Database($this->config->dbhost);
}
}
class Configuration {
var $dbhost = 'localhost';
}
class Database {
function __construct($dbhost) {
echo $dbhost;
}
}