If I create a registry object to store other objects and settings in like this...
$registry = Registry::getInstance();
And then create 2 other objects and pass the Registry object into them like this below...
$core = new core($registry);
$database = Database::getInstance($registry);
and then later in the script I add some objects to the Registry object...
// Store some Objects into our Registry object using a Registry Pattern
$registry->storeObject("database", $database);
$registry->storeObject("session", $session);
$registry->storeObject("cache", $cache);
$registry->storeObject("user", $user);
Will methods in the core and database objects that were created at the top, still have access to all the objects that I store into the registry even though the other objets were stored into the registry AFTER the core and database Objects were created?
yes they will, objects are passed by reference (in php >= 5) so, each variable will refer to the same underlying object.
in old php, you would need to pass by ref:
$obj->registry =& $registry;
function f(& $registry) { // $registry is a reference }
the key in php <5 is the ampersand syntax when assigning and in function declarations.
If its the same instance of the object, than yes - otherwise they'll have to use shared memory to pass the objects around or no, you won't have access to them.
However, I'd imagine your registry is a singleton right? So yes.
edit: maybe Im not understanding your question ....
Yes, they'll have access to these object, but IMO Registry isn't the best solution here - Context would be much better because it allows you to model each property. It also gives you 100% sure that when you call $registry->get('user') some User object will be returned.
Context is pretty similar to Registry:
class Context {
protected $database;
protected $user;
protected $logger;
public function setDatabse(PDO $database) {
$this->database = $database;
}
public function getDatabase() {
return $this->database;
}
public function setLogger(Logger $logger) {
if ($logger instanceof MySpecificLogger) {
// do sth
}
$this->logger = $logger;
}
// rest of setters/getters
}
And when you use it later:
$db = $contextObject->getDatabase();
When you use Registry you don't have 100% sure that $db is then an object of PDO (in this example) what might causes some problems in some situations.
No, not by default. Parameters are passed by value in PHP in almost every case. What you want is called "passing by reference", which you can read more about in the manual.
Related
let's say i have this class:
class DB {
private DBConnection $connection;
private string $databaseName;
public function __construct($databaseName) {
$this->databaseName = $databaseName;
}
private function initConnection(): void {
if (!isset($this->connection)) {
$this->connection = new DBConnection($this->databaseName);
}
}
public function query($str): array {
$this->initConnection();
return $this->connection->query($str);
}
public function something(): void {
$this->initConnection();
$this->connection->something();
}
}
Then I have some code that may or may not call the ->query / ->something methods, depending on the situation.
How can I avoid calling initConnection in every single place where $this->connection has to be used?
I only want to initialize it IF it is accessed, on its first access.
I already tried with the magic method __get but it only gets called if $connection is not in the class definition.
Another way is to create an accessor method (getConnection) which calls initConnection and use $this->getConnection() (returning the connection object, instead of void) instead of $this->connection, but still, initConnection would get called for nothing.
The problem with this approach is that I could accidentally still use $this->connection instead of the getter method; is there a way I can disallow the direct use of the property?
In my opinion, you are correct by concluding to use a (private) getConnection method to instantiate the connection only on its first use. And have the rest of the class method use getConnection() instead of $this->connection.
However, I also believe you are experiencing the downside of the singleton pattern. Perhaps consider refactoring out the actual DBConnection, and pass it as a constructor argument (dependency) to DB. You can then provide implementations of DBConnection that support lazy loading and singletons.
Why we can instantiate non-exist variable? What's the different when declare all properties on class and then assign value to it.
class hello {
public function __construct($db) {
$this->db = $db;
}
public function set($db) {
$this->db = $db;
}
public function get() {
return $this->db;
}
}
This isn't quite the same as using a non-existent variable - a non-existent variable will raise a notice in PHP. In your case, $this already exists, so setting a property on it just quietly creates a public property for your object. It's rather like an array that you add a new key-value pair to - you wouldn't expect that to raise a notice either.
If you know beforehand what properties you need, then yes, do declare them explicitly. In this case, you would probably want this to be protected, which you don't get if you don't declare. (Often people use private here, which means that a child class cannot access the property - though that's okay if you want to force descendants to use the getter).
The flexibility to add properties to objects can be useful if you don't know in advance what properties you'll want to store. For example, some ORMs use one class for all tables, and an instance of that class is used to store the column-value pairs for a row.
In PHP, I have two classes: Database and Item.
Database contains the connection properties and methods. For example, Database::Query can be used to pass a query string, etc.
Item is a generic item identifier. It's built by passing it an itemID which is then used to query the database for the rest of the item information.
In this case, what's the best practice for creating Item objects if they require database access? Is it normal to create each one using this syntax:
$item = new Item(12345, $db);
Or is it better, acceptible, or possible to create the Database object and have it used for each Item created in the application, such that the call could become:
$item = new Item(12345);
The second seems a lot cleaner (and can be expanded so that similar types of objects don't also need that $db addon), but I'm looking for suggestions from those who have more experience at this than I do! Thanks!
I would suggest that most seasoned developers would lean toward the approach of dependency injection as demonstrated in your first example.
Why?
Well largely because this allows you to decouple the class to which the dependency is being injected from the dependency's implementation.
So consider this dependency injection example:
Class some_class {
protected $db;
__construct($db) {
if($db instanceof some_db_class === false) {
throw new Exception('Improper parameter passed.');
}
$this->db = $db;
}
}
Here you could pass any type of object so long as it was an instance of some_db_class it could be a subclass of that object that implements the same methods used by this class. That doesn't matter to this class as long as the methods are implemented (you of course could also check that a passed object implements a specific interface in addition to or in lieu of checking its instance type).
This means that, for example, you can pass a mock DB object for testing or something like that. The class doesn't care as long as the methods are implemented.
Now consider the singleton approach (or similar instantiation of DB from with the class):
Class some_class {
protected $db;
__construct() {
$this->db = some_db_class::get_instance();
}
}
Here you have tightly coupled your class to a specific database class. If you wanted to test this class with a mock DB implementation it becomes very painful in that you need to modify the class to do so.
I won't even get into discussion of using global as that is just poor practice and should not be considered at all.
I would recommend using the Singleton Pattern for your database connection. This is actually the best practice. As you really dont need to instances of your database connection.
class Database_Instance
{
private static $database;
public static function getDatabaseObject() {
if (!self::$db) {
self::$db = new PDO( );
}
return self::$db;
}
}
function callWhatSoEver()
{
$connection = Database_Instance::getDatabaseObject();
}
For more information about the singleton pattern, see: http://en.wikipedia.org/wiki/Singleton_pattern
Typically a database connection object is global, or accessible globally. That works well for the vast majority of applications.
I do something like this (simplified for example purposes):
$db = connect_to_db();
function GetDB()
{
global $db;
return $db
}
//inside the item object
function Load( $id)
{
$db = GetDB();
$db->query(..);
}
There are, of course, cases where this isn't the best route. As always, it depend on the specific needs of your application.
I'm in the process of re factoring a lot of code to make it more testable and I have a bunch of useful functions that rely on an instantiated database object.
Things like this:
function id_from_name($table, $name)
{
$db = get_database();
//code that returns an id
}
function username_from_user_id($id)
{
$db = get_database();
//code that returns a username
}
There are a bunch more like id_exists, id_active etc.
Now I'm thinking that this isn't the right thing to do as the object should probably be passed through as an argument? But then that means creating and sending in a new object into each of these functions every time i want to use one.
So really, my questions are: Should I be moving these functions into their own class/library that has access to the database object? and are the examples that I've shown above generally a bad way of doing things?
A better approach would be indeed to make classes. And you would be passing the database object to the constructor and make it an instance variable. That way every function would have access to the database object.
Now the reason why it is considered bad to instantiate e.g. your database object in every function, is because if you decide for example one day to change your datasource, you might need a huge refactor. If you pass your database object into the constructor, you can just pass/inject the right object into the class without any refactor.
...a bit more about DI below...
By passing your objects into the constructors, you also create a more clear API => you know which object depends on the other, you know exactly which class uses your DB object. If you start instantiating it or accessing it in a static way inside the functions like you did, I would have to look through all your classes to see where your DB object is used. One more point, dependency injection forces SRP (single responsibility principle) => if you start injecting too many objects (constructor gets many arguments), you should suspect your class is doing too much than what it should, and start refactoring.
You can create a class Table_Adapter and instantiate database object inside its constructor:
class Table_Adapter
{
protected $db;
public function __construct()
{
$db = get_database();
}
}
Then you create a child class Items_Table_Adapter' that extendsTable_Adapterand put their all methods related toItems` table.
class Items_Table_Adapter extends Table_Adapter
{
public function item_by_id($id)
{
}
}
Then you use it like:
$tableAdapter = new Items_Table_Adapter();
$item = $tableAdapter->item_by_id(1);
Try something like:
class YourClass{
public static function get_database(){
// your creation
return $db;
}
public function id_from_name($table, $name)
{
/* your code */
//code that returns an id
}
public function username_from_user_id($id)
{
/* your code */
}
}
so you could just use it this way:
$db = YourClass::get_database();
$result = $db->id_from_name($table, $name);
It is certainly recommended that you have the option to swap out your database connection.
Now, if your function get_database() looks like this:
function get_database() {
static $db;
if (!$db)
$db = new \mysqli(...);
return $db;
}
Then you really, really should change it to a wrapper around a class, looking like this:
function get_database_manager() {
static $dbmgr;
if (!$dbmgr)
$dbmgr = new DbManager;
return $dbmgr;
}
function get_database() {
return get_database_manager()->getCurrentConnection();
}
where DbManager has an instance attribute with the current connection that is returned with getCurrentConnection(). If you want to swapt out the connection, do something like get_database_manager()->setConnection($newConn). Problem solved :)
I'll leave the downsides of static programming here (it remains with many examples in this thread): http://kunststube.net/static/
as well as the common method to get rid of that (we have another approach here): http://en.wikipedia.org/wiki/Dependency_injection
I have a class userdb in which I am declaring a function that returns the connection to the database:
return $con = new PDO("mysql:host=$host;dbname=$db", $user, $pass);
I have various functions, even across other classes, where I have to access $con (e.g. to pass a query or to fetch data), but I can't access this variable.
Is there a better way to define and use a database class? Remember that I have other classes where I need to access the userdb class.
I would advise you to use the Singleton Pattern for this:
In your userdb class, declare a static property $scon:
private static $scon;
and assuming the function you mention above is named createConnection(), you should create the folowing static method:
public static function connect() {
if (empty(self::$scon)) {
$instance = new userdb();
self::$scon = $indtance->createConnection();
}
return self::$scon;
}
With this, you will be able to access your userdb connection with:
userdb::connect();
Also since this is a singleton, it will only connect once, and use that connection until the end of the script.
Note (on dependency injection): Since #KevinM1 mentioned Dependency Injection, I must add that it is also a possible, and far superior solution. It requires you to create a setConnection() method (or an Abstract ancestor) for all your classes using a database connection, and during the instatiation of these classes you may use a Factory to add the required connection to the object. This should be wrapped inside some class loader, which is avare of your model structure.
See, peace of cake, but for small and fast developement I would stick with the Singleton ;)
If it's in a class, store the instance in a property:
class userDB
{
public $dbCon = false;//because you want to access the instance
//from outside the class, I have made the property public
function connect()
{
$con = new PDO("mysql:host=$host;dbname=$db", $user, $pass);
$this->dbCon = $con;
}
}
TO access it outside of the class:
$useDBInstance->dbCon;
return $this->con
return this way from your class and call it this way..
$this->classObject->con->prepare();
Checkout my video tutorial + code for an alternative to global PHP variables.
You're doing it wrong there. You need to use a static variable if you plan to create your connection in a function and store it there. Otherwise you'll keep connecting on every function call. My tutorial explains this very concept of static variables within regular functions.
If it's not clear enough, let me know and I'll try to answer your questions.
Here's some code to accompany this:
/**
* Arguments are none or [$db, [$user, [$pass[, $host]]]].
*
* #return PDO
*/
function PdoDb(){
static $con = null; // I'm explicit :)
// Every time you pass Arguments you reconnect
if(func_num_args()){
$args = array_pad(func_get_args(), 4, null);
list($db, $user, $pass, $host) = $args;
if(empty($user)) $user = 'root';
if(empty($host)) $host = 'localhost';
$con = new PDO("mysql:host={$host};dbname={$db}", $user, $pass);
}
if(empty($con)){
trigger_error('Provide arguments to connect first.', E_USER_ERROR);
return null;
}
return $con;
}
// First run (provide arguments to connect)
PdoDb($db, $user, $pass, $host);
PdoDb($db); // Works if you connect root#localhost with no password
// From here on (it returns PDO)
PdoDb()->DoStuffOfPdo();
Once connected it stays that way. But you can reconnect at will to by providing arguments.
Well, $con will already be an object, as it's instantiating a new PDO object. Unless you're trying to add functionality to your PDO object, wrapping it is pointless.
That said, the best way to share your userdb/PDO object (depending on whether or not you stick with the wrapper) with other objects is to use Dependency Injection. That's a fancy term for passing your db to whatever object needs it. Since objects are defaultly passed by reference in PHP, if you create your db object first, all objects that receive it as a constructor/method argument will be using that same single instance.
EDIT: Link to Dependency Injection implementation
EDIT2: Clarification on DI in small projects -
The normal DI pattern generally requires a special object called a DI Container. This is a special use object that automatically injects the dependency into the object that needs it. For small projects, it's overkill. The simple, low complexity version of DI is simply:
class SomeClass {
protected $db;
public function __construct($db) {
$this->db = $db;
}
}
class SomeClass2 {
public function SomeMethod($db) {
// do something with the db
}
}
$db = new PDO(/* connection string */);
$obj = new SomeClass($db, /* other constructor args */);
// or
$obj2 = new SomeClass2(/* constructor args */);
$obj2->someMethod($db, /* method args */);
The magic is that since objects are passed by reference by default in PHP, $obj and $obj2 are using the same db connection.
The whole idea is to not blow apart scope or encapsulation by having a static method, and to ensure that classes and their methods are up front about what they require in order to work.
Singletons do the exact opposite. They're accessed through static methods, which bypass scope, and since they're invoked and not passed, they never show up in method signatures, so anyone not familiar with the code won't be aware of that hidden requirement. Even Erich Gamma, one of the people who helped codify the Singleton Pattern has regrets about it:
I'm in favor of dropping Singleton. Its use is almost always a design smell.
In PHP, where there's no concept of shared memory, and where scripts execute once per request, the only reason to want to use a singleton is to have easy access to a single resource. Since objects are passed by reference, a single instance can be shared with multiple objects naturally. From there, it's about good design and delegation.
use singlton class implimentation
class connectdb
{
protected static $_instance = NULL;
private function __construct()
{
}
public function getinstance()
{
if (null === self::$_instance) {
self::$_instance = new self();
}
return self::$_instance;
}
public function connect()
{
$this->connection =new PDO("mysql:host=$host;dbname=$db", $user, $pass);
}
}
for using a variable within a class function or independent function you need to place a global keyword
$conn=mysql_connect();
function test(){
global $conn;
}
now $conn will be available within the scope of test function, and it will be available everywhere when defined at the top of the script. For class also you need to do the same thing, make a object of a class and declare it as global within a function