So recently I've really started to use php actively, and I need some insights on different ways to use database connections.
At first I just used the simple mysql_connect():
<?php
$connection = mysql_connect(DB_HOST, DB_USER, DB_PASS) or die(mysql_error());
mysql_select_db(DB_DB, $connection);
?>
After a while I created a database class which I started to include and initialize in every file - something like this:
<?php
class MySQL_DB {
var $connection;
function MySQL_DB(){
$this->connection = mysql_connect(DB_HOST, DB_USER, DB_PASS) or die(mysql_error());
mysql_select_db(DB_DB, $this->connection);
}
function query($q){
$res = mysql_query($q, $this->connection) or die(mysql_error());
return $res;
}
}
$database = New MySQL_DB;
?>
And this is what I'm using at the time - and it's working fine - but there are always ways to improve.
So my question to you is how do you manage your database connections?
Do you use classes?
What does your classes contain (just
the connection or even functions?)
What practices do you recommend?
I recommend to use PDO. Don't reinvent the weel. It's a nice OO-interface to many database engines.
Additionally I create a small function which just inititializes PDO object. So all connection settings can be changed in one place.
Your current approach is pretty standard, and works well. I used it for a long time. It's true that modules like PDO provide base functionality like this now, which is very nice as well and can get you away from problems with home-brew code.
However, I've taken the connection management one step further. If you get into a complex application, you might get into a situation where you have multiple databases, or heavy database use. Including a single database connection file and having a global $database variable becomes unwieldy for multiple databases, and it's unnecessary for application requests that might not need a database connection. Remember, connecting to the database is expensive.
What I've done is create a singleton DatabaseManager class that handles the database object for me, and makes sure multiple connections to a given DB don't get instantiated. Instead of initializing a new database object at the top of your app, you simply call on the DatabaseManager every time you need the object.
$db = DatabaseManager::getDatabase();
Here's an example class that I had whipped up for a CodeIgniter project. You can see in the getDatabase() function it simply loads CodeIgniter's default database object, which you would substitute for your own class (and run the connection routine for it) if you weren't using CI. This is a pretty simplistic management class, and could be extended to manage multiple connections to different databases fairly easily.
<?php
/**
* Implements the Singleton pattern to prevent multiple instantiations and connections
* to the application database.
*
*/
class Database_manager
{
private static $instance;
public $db;
/**
* Constructor function is declared private to prevent instantiation.
*
*/
protected function __construct()
{
parent::__construct();
}
/**
* Returns an instance of a Database_manager.
*
* #return object Database_manager object
*/
public static function getInstance()
{
if (self::$instance == null) {
$className = __CLASS__;
self::$instance = new $className();
}
return self::$instance;
}
public static function getDatabase()
{
$instance = self::getInstance();
if ($instance->db == null) {
//utilize CodeIgniter's database loader
$instance->db = $instance->load->database('',true);
if (! is_object($instance->db)) throw new Exception("Could not load database.");
}
return $instance->db;
}
}
Perhaps the most common advantage I get out of using this style of connection management is when I have to take down an application for database maintenance. By not instantiating a database connection until I need it, I can easily put up a "maintenance in progress" message on a site (short circuiting normal MVC dispatching), and not worry about requests to the application opening a DB connection while maintenance is in progress.
Usage of classes are the way to go to increase customized re-usability.
Bring in all generic implementations into the class. You are on the right track.
This website has the following clean approach.
This website link is no longer present. Archive Link.
class connection {
// Possible Modules are as follows:
// DBX_MYSQL, DBX_ODBC, DBX_PGSQL, DBX_MSSQL, DBX_FBSQL, DBX_SYBASECT, DBX_OCI8, DBX_SQLITE
private $module = DBX_MYSQL;
private $host = "localhost";
private $database = "test";
private $username = "testuser";
private $password = "testpass";
private $link;
private $result;
public $sql;
function __construct($database=""){
if (!empty($database)){ $this->database = $database; }
$this->link = dbx_connect($this->module,$this->host,$this->database,$this->username,$this->password);
return $this->link; // returns false if connection could not be made.
}
function query($sql){
if (!empty($sql)){
$this->sql = $sql;
$this->result = dbx_query($this->link,$sql,DBX_RESULT_UNBUFFERED);
return $this->result;
}else{
return false;
}
}
function fetch($result=""){
if (empty($result)){ $result = $this->result; }
return dbx_fetch_row($result);
}
function __destruct(){
dbx_close($this->link);
}
}
In your database manager example, you did not define a parent for your class.
Therefore, invoking parent::__constructor() yields an exception,
and also, you cannot use the load property of code ignitor.
Which class did you use as an extension for your DatabaseManager?
Since i do not know where you placed your databasemanager code, nor which class you used as its parent, i circumvented the exceptions by making the getDatabase() method receive an input parameter which i called $loader.
Normally, this $loader object will be the model class requiring access to a database.
public static function getDatabase($loader)
{
$instance = self::getInstance();
if ($instance->db == null) {
//utilize CodeIgniter's database loader
$instance->db = $loader->load->database('default',true);
if (! is_object($instance->db)) throw new Exception("Could not load database.");
}
return $instance->db;
}
Best regards.
Related
I'm pretty new to classes and struggling to connect a simple function to another function. Whenever I add an echo 'test' inside the ConnectDB function it passes through the 'test'. However, it doesn't include the include files.
It's probably a noob mistake.
Note: When I copy/paste the content from ConnectDB to the UpdateFollowers function it works. I'm looking for a way to save time without using an include file.
class UpdateAccountInfo {
public function ConnectDB() {
if (strposa($_SESSION['geturl'], $_SESSION['folders']) != FALSE) {
include '../_includes/config.php';
include '../_includes/opendb.php';
} else {
include './_includes/config.php';
include './_includes/opendb.php';
}
}
// update followers
public function UpdateFollowers($getid) {
$this->ConnectDB();
//find the source of the ig account
$sql = "SELECT * FROM ig_accounts WHERE iid = $getid";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
// output data of each row
while($row = $result->fetch_assoc()) {
$igname = $row["igname"];
}
............
What is a class?
Before going into any explanation concerning the case at hand, I think it's important to get some OOP concepts straight first. From the example in the question, I get the feeling that your understanding of classes is that they simply are "function buckets" so to speak. This isn't the case. A class is a generic data structure you can use to define objects, behavior related to those objects and data used by those objects.
class Human {
private $firstName;
private $lastName;
private $dateOfBirth;
public function __construct($fn, $ln, $dob) {
$this->firstName = $fn;
$this->lastName = $ln;
$this->dateOfBirth = $dob;
}
public function getFullName() {
return $this->firstName.' '.$this->lastName;
}
}
In the example above, we've defined a basic structure shared by all objects of type Human as well as encapsulated some very basic functionalities (getting the full name of our Human).
If we take a look at your example, UpdateAccountInfo is more of a functionality rather than an object. It is a process that will always be performed by some other component of the system, for the purpose of this example let's call that other component an Account.
class Account {
private $id;
private $name;
private $conn; // <-- our DB connection
/* other Account properties */
public function __construct($id, $name) {
$this->id = $id;
$this->name = $name;
/* Initialize DB connection */
}
public function updateFollowers() {
/* Perform any logic required to update the followers */
}
}
Now we have an object of type Account to which we add however many functions we need in the future. addFollowers(), removeFollowers(), changeUsername(). Those are all examples of processes that belong to the Account object and will likely never be used by any other component of the system.
Initializing the Database connection
You may have noticed that I have left out the database initialization part out of the previous example. There is a few reasons for this but mainly:
Opening and closing a connection each time create an instance of Account (or any object for that matter) using the new keyword is very costly.
It breaks the Single Responsibility Principle. I won't get into that too much as it is a pretty lengthy topic. What you need to know for the time being is that it essentially means that an object should only deal with its own data/processes, and no more. In this case, opening a database connection simply isn't the job of Account.
To get around this, we can simply encapsulate the database connection logic in a Database object.
class Database {
private $connection;
public function connect($localhost, $name, $password, $database) {
$this->connection = new mysqli($localhost, $name, $password, $database);
if($this->connection->connect_error) {
/* throw an exception */
}
}
public function getConnection() {
return $this->connection;
}
}
Now you simply need to initialize the database connection once at the beginning of the script, and pass it around to other objects/functions that may need it.
<?php
include_once('../../config.php');
/* include any other required files */
$database = new Database($config['localhost'], $config['username'], $config['password'], $config['dbname']);
// get a specific account
$account = new Account(/* ... */, $database);
// update the account's followers
$account->updateFollowers(/* ... */);
If we want to modify a second account, we can do so using the same database connection we just opened.
<?php
/* ... code from previous example ... */
// initialize a new Account with the same Database
$otherAccount = new Account(/* new account's info */, $database);
$otherAccount->updateFollowers(/* ... */);
Further readings
PHP documentation on OOP
Wikipedia page on Single Responsibility Principle
How to initialize a database connection
A couple of the options are:
$connection = {my db connection/object};
function PassedIn($connection) { ... }
function PassedByReference(&$connection) { ... }
function UsingGlobal() {
global $connection;
...
}
So, passed in, passed by reference, or using global. I'm thinking in functions that are only used within 1 project that will only have 1 database connection. If there are multiple connections, the definitely passed in or passed by reference.
I'm thining passed by reference is not needed when you are in PHP5 using an object, so then passed in or using global are the 2 possibilities.
The reason I'm asking is because I'm getting tired of always putting in $connection into my function parameters.
I use a Singleton ResourceManager class to handle stuff like DB connections and config settings through a whole app:
class ResourceManager {
private static $DB;
private static $Config;
public static function get($resource, $options = false) {
if (property_exists('ResourceManager', $resource)) {
if (empty(self::$$resource)) {
self::_init_resource($resource, $options);
}
if (!empty(self::$$resource)) {
return self::$$resource;
}
}
return null;
}
private static function _init_resource($resource, $options = null) {
if ($resource == 'DB') {
$dsn = 'mysql:host=localhost';
$username = 'my_username';
$password = 'p4ssw0rd';
try {
self::$DB = new PDO($dsn, $username, $password);
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
} elseif (class_exists($resource) && property_exists('ResourceManager', $resource)) {
self::$$resource = new $resource($options);
}
}
}
And then in functions / objects / where ever:
function doDBThingy() {
$db = ResourceManager::get('DB');
if ($db) {
$stmt = $db->prepare('SELECT * FROM `table`');
etc...
}
}
I use it to store messages, error messages and warnings, as well as global variables. There's an interesting question here on when to actually use this type of class.
Try designing your code in an object-oriented fashion. Methods that use the database should be grouped in a class, and the class instance should contain the database connection as a class variable. That way the database connection is available to the functions that need it, but it's not global.
class MyClass {
protected $_db;
public function __construct($db)
{
$this->_db = $db;
}
public function doSomething()
{
$this->_db->query(...);
}
}
I see that a lot of people have suggested some kind of static variable.
Essentially, there is very little difference between a global variable and a static variable. Except for the syntax, they have exactly the same characteristics. As such, you are gaining nothing at all, by replacing a global variable with a static variable. In most examples, there is a level of decoupling in that the static variable isn't referred directly, but rather through a static method (Eg. a singleton or static registry). While slightly better, this still has the problems of a global scope. If you ever need to use more than one database connection in your application, you're screwed. If you ever want to know which parts of your code has side-effects, you need to manually inspect the implementation. That's not stuff that will make or break your application, but it will make it harder to maintain.
I propose that you chose between one of:
Pass the instance as arguments to the functions that needs it. This is by far the simplest, and it has all the benefits of narrow scope, but it can get rather unwieldy. It is also a source for introducing dependencies, since some parts of your code may end up becoming a middleman. If that happens, go on to ..
Put the instance in the scope of the object, which has the method that needs it. Eg. if the method Foo->doStuff() needs a database connection, pass it in Foo's constructor and set it as a protected instance variable on Foo. You can still end up with some of the problems of passing in the method, but it's generally less of a problem with unwieldy constructors, than with methods. If your application gets big enough, you can use a dependency injection container to automate this.
My advice is to avoid global in the bulk of the code - it's dangerous, hard to track and will bite you.
The way that I'd do this is to have a function called getDB() which can either be at class level by way of a constructor injection or static within a common class.
So the code becomes
class SomeClass {
protected $dbc;
public function __construct($db) {
$this->dbc = $db;
}
public function getDB() {
return $this->dbc;
}
function read_something() {
$db = getDB();
$db->query();
}
}
or using a common shared class.
function read_something() {
$db = System::getDB();
$db->query();
}
No matter how much elegant system design you do, there are always a few items that are necessarily global in scope (such as DB, Session, Config), and I prefer to keep these as static methods in my System class.
Having each class require a connection via the constructor is the best way of doing this, by best I mean most reliable and isolated.
However be aware that using a common shared class to do this can impact on the ability to isolate fully the objects using it and also the ability to perform unit tests on these objects.
None of the above.
All the mysql functions take the database connection argument optionally. If you leave that argument out, the last connection by mysql_connect() is assumed.
function usingFunc() {
$connection = getConnection();
...
}
function getConnection() {
static $connectionObject = null;
if ($connectionObject == null) {
$connectionObject = connectFoo("whatever","connection","method","you","choose");
}
return $connectionObject;
}
This way, the static $connectionObject is preserved between getConnection calls.
I'm moving onto teaching myself OOP in PHP.
I'm creating a couple of little web apps and have followed a lot of tutorials that either create the database (using PDO) via a Singleton, or via passing the global around. I've read that these are pretty much the same thing and are both to be avoided like the plague.
So I've watched the Google Tech Talks on clean code, and read almost every SO article on dependency injection and the like. I have a couple of questions.
The clean code videos suggest you shouldn't do 'work' in your constructors. Is this 'work' in reference to business logic. Ie. If my class's job is to create another object, is that an OK kind of 'work'?
For example, in trying to conform to single repsonibility classes I created three.
Class DB - which actually connects to the database.
Class DBFactory - which creates the DB object which connects to the database.
Class DBInstance - which returns a single instance of the DBFactory created PDO object.
Please note that I'm trying to create a single instance, without creating a Singleton pattern.
So I try and pass my dependencies for each class up the chain. I find myself in a position where I have to create all of the objects (from DB down) so I can inject the dependencies. For some reason I thought it would work the other way, I'd create the first object, which would create the second for me etc. I'm clearly missing something?
Hopefully this helps others as well - there seems to be a myriad of questions relating to this stuff and databases but very little good examples.
(I should mention this does work, I do get a list of hotel names out of the database!)
TestCode.php
include './classes/DB.php';
include './classes/DBFactory.php';
include './classes/DBInstance.php';
include './classes/Location.php';
$db = new DB;
$dbfactory = new DBFactory($db);
$dbinstance = new DBInstance($dbfactory);
$dbh = $dbinstance->getDbInstance();
//Example business logic
$location_names = Location::getLocationNames($dbh);
print_r($location_names);
Class DB.php:
class DB {
private $_dbhost = 'myhost';
private $_dbname = 'myname';
private $_dbuser = 'myuser';
private $_dbpass = 'mypass';
private $_error;
public function connect() {
try {
return new PDO("mysql:host=$this->_dbhost;dbname=$this->_dbname",
$this->_dbuser, $this->_dbpass);
}
catch (PDOException $e) {
$this->_error = 'Error! ' . $e->getMessage() . '<br />';
die();
}
}
public function getError() {
if (isset($this->_error)) {
return $this->_error;
}
}
}
Class DBFactory.php
class DBFactory {
private $_dbh;
public function __construct(DB $db) {
$this->_dbh = $db;
}
public function Create() {
return $this->_dbh->Connect();
}
}
Class DBInstance.php
class DBInstance {
private static $_dbinstance;
public function __construct(DBFactory $dbfactory) {
if (!isset(self::$_dbinstance)) {
self::$_dbinstance = $dbfactory->Create();
}
}
public function getDbInstance() {
return self::$_dbinstance;
}
}
Your code seems to do what you want it to.. but maybe we can use less object instantiation using inheritance and maybe we can avoid static properties in instanciated classes.
Also in regard to using a pattern of dependency injection that is able to handle multiple connections, but support using a single instance of it. exemple first, classes after
$params = array
('host'=>'localhost',
'db'=>'ice',
'user'=>'kopitar',
'pass'=>'topnet',
'charset'=>'utf8'); // passing the charset explicitely is great
$handle = new handle($params);
$db = $handle->getInstance();
we can either pass the $db to our functions
$location_names = Location::getLocationNames($db);
or the whole $handle. as long as $handle is not reconstructed, it will always return the same database connection.
$location_names = Location::getLocationNames($handle);
if I want to reconstruct I need the whole $handle
$handle->__construct(/* params but with another database infos */);
$db2 = $handle->getInstance();
As for the classes, I think we want the params to arrive from the instanciated class, so we can change them later.
class db {
function __construct($params) {
foreach ($params as $param => $value) {
$this->{$param} = $value; // assigns the connections infos
}
}
protected function connect() {
$dsn = 'mysql:host='.$this->host.';dbname='.$this->db.';charset='.$this->charset;
return new PDO($dsn,$this->user,$this->pass);
}
}
the factory creates a connection from params and passes it to something else, good factory
class factory extends db {
protected function create() {
return $this->connect();
}
}
now we want to have our object to keep it's connection as long as we do not rebuild it. so we give it to instance
class instance extends factory {
function instantiate() {
$this->instance = $this->create();
}
}
and last but not least, our handle which returns the instance. it could be in instance class.....................
but I feel like having four and find no real reason not to.
class handle extends instance {
function __construct($params) {
db::__construct($params);
$this->instantiate(); // when we construct a handle, we assign an instance to the instance property
}
function getInstance() {
return $this->instance;
}
}
KISS
Don't make things more complex than they are, of course this is just my opinion, but as I see it you are building a complex solution for a problem that someone else says might exist is some cases.
Php is not multi threaded so there goes one of the biggest arguments overboard. (in very rare-occasions it might be)
I'm using singletons for my database connections for about 15 years now and never ever had a problem with them, I do play around with different connections having one singleton handle several connection instances, but whatever... it works great and everyone that looks at the code.. understands it directly.
I'm not using globals because they can be overwritten and are kind of hard to predict (when it holds the correct object, and when/why they don't)
Use OOP to make your code cleaner, easier to work with and more flexible.
Don't use it to fix problems that aren't there and make your code more complex because others tell you to.
An very simple example of a db-connection singleton class handling several different connections.
class singleton{
private static $_instances=array();
public static function getInstance($connectionName){
if(!isset(self::$_instance[$connectionName]){
self::$_instance[$connectionName]=self::_getConnection($connectionName);
}
return self::$_instance[$connectionName];
}
}
just my 2 cents
Why do you have a factory if you have a singleton? This is needless.
This is a never-ending debate, but I'm advocate of do not use singletons for database connections.
As far as in most applications, you have only one data channel, you can consider your database connection unique, but this might not be always true.
In deed, the effort made to create a singleton database connection is even bigger than just create a regular one.
Also, your class DB is not configurable, therefore, you need to change it when your connection parameters change. And I think DB is a very bad name for this.
I'd rather call this Storage and do something like:
inteface Storage {
public function insert($container, array $data);
public function update($container, array $data, $where);
public function delete($container, $where);
public function getAll($container);
public function getOne($identifier);
}
final class PdoStorage implements Storage {
private $dbh;
private $dsn;
private $user;
private $pswd;
public function __construct($dsn, $user, $pswd) {
$this->dsn = $dsn;
$this->user = $user;
$this->pswd = $pswd;
}
// Lazy Initialization
private function connect() {
if ($this->dbh === null)
$this->dbh = new PDO($this->dsn, $this->user, $this->pswd);
}
public function insert($container, array $data) {
$this->connect();
// ... omitted for brevity
}
}
Now, when you need a database storage, you do:
$someObj = new SomeClass(new PdoStorage(...));
Now you might be wondering if you will need to create an PdoStorage for each single object that depends on it.
The answer is: no!
Now you can use a factory to simplify your life.
class SomeFactory {
private $defaultStorage;
public function __construct(Storage $storage) {
$this->defaultStorage = $storage;
}
public function create($type) {
// Somehow fetches the correct class to instantiate and put it into $class variable , for example... and then
return new $class($this->defaultStorage); // Or you'd better do this with reflection
}
}
$factory = new SomeFactory(new PdoStorage(...));
$factory->create('SomeClass');
This way, you can have just one database connector or more if you need.
I have a class called DB (class.pdo.php) that does all the handling on mysql queries using PDO and another class called user that I use to manage a login system.
My question relates to always having to instantiate the $db in every public function of users so I can use DB. Is this efficient? Shouldn't I be instantiating DB inside the __construct() of users?
This is my code
require_once("../../class.pdo.php");
class user {
private $db = null;
public function __construct(){
/* Empty? */
}
public function find_by_email($email){
$db = new db();
$db->query('SELECT * FROM users WHERE email = :email LIMIT 1');
$db->bind(':email',$email);
$result = $db->single();
return $result;
}
public function create($email,$password,$first_name,$last_name){
$db = new db();
$db->query("INSERT INTO users(email,password,first_name,last_name,created_at) VALUES (:email,:password,:first_name,:last_name,NOW())");
$db->bind(':email',$email);
$db->bind(':password',$password);
$db->bind(':first_name',$first_name);
$db->bind(':last_name',$last_name);
$result = $db->execute();
return $db->lastInsertId();
}
[more similar functions ommited]
Well, despite of some comments suggesting the use of the Singleton pattern, I totaly disagree in using it for this purpose.
Your application will not always use a single connection to just one database.
Let me show you how I'd do this:
class DbConnector {
private $dbh;
private $dsn;
public function __construct($dsn) {
$this->dsn = $dsn;
}
private function connect() {
if($this->dbh === null) {
$this->dbh = new PDO($this->dsn);
}
}
public function disconnect {
if($this->dbh !== null) {
$this->dbh = null;
}
}
public function query($sql) {
$this->connect();
//... do the rest
}
public function fetchAll($sql) {
$this->connect();
//... do the rest
}
public function insert($table, $values) {
$this->connect();
//... do the rest
}
public function update($table, $values, $cond) {
$this->connect();
//... do the rest
}
public function delete($table, $cond) {
$this->connect();
//... do the rest
}
}
class User {
private $dbConn;
public function __construct(DbConnector $dbConn) {
$this->dbConn = $dbConn;
}
public function create($email,$password,$first_name,$last_name){
$this->dbConn->query("INSERT INTO users(email,password,first_name,last_name,created_at VALUES (:email,:password,:first_name,:last_name,NOW())");
$this->dbConn->bind(':email',$email);
$this->dbConn->bind(':password',$email);
$this->dbConn->bind(':first_name',$email);
$this->dbConn->bind(':last_name',$email);
$this->dbConn->execute();
return $this->dbConn->lastInsertId();
}
// ...
}
Results:
No singleton used = testable.
Connection to the database is just openned when needed
Your connection is persistent. If you open and close connections in every method, you loose the capability of creating transactions.
What about using the Singleton pattern to create one object for the connection and use it everytime you need it, instead of creating new objects all the time?
I would do something similar with lazy loading: don't initiate in the constructor unless you're sure you actually need the connection every time an object is created but absolutly don't create a new object on each method call. Instead, save the resulting object into an object var which is checked on each method call and initiates the connection if missing.
class user {
protected $_db = null;
private function _init_db() { $this->_db = new XXX; }
public function create( $x, $y, $z ) {
if ( ! $this->_db ) $this->_init_db();
# use $this->_db ..
}
public function find_by_email( $x, $y, $z ) {
if ( ! $this->_db ) $this->_init_db();
# etc
}
}
This has the advantages of avoiding global static state (singletons..) and only creates the connection / object at the very last moment so you're sure you actually need it and it's not just a useless connection.
Speaking of efficiency, the main problem with your code is that it establishes new connection for the every method called. This one is indeed inefficient to the point of killing your database server. And it's incomparable to the other problem you have.
So, in general, you can have whatever way you want - either get somehow an instance of db class in the every function or use a class variable - but either way have to use single PDO instance throughout whole application.
Also I find your functions quite inefficient from the amount of code point of view, and would have optimized them this way
public function create($email,$password,$first_name,$last_name){
$sql = "INSERT INTO users(email,password,first_name,last_name,created_at) VALUES (?,?,?,?,NOW())";
$this->db->query($sql);
$result = $db->execute(func_get_args());
return $db->lastInsertId();
}
From a object point of view, I'd leave database instantiating within the methods, rather than an entire class.
Each method should only see the variables and data it needs, in order to perform its function.
For instance, a createUser() method would need to see variables or properties such as $username, $usergroupId, as well as $database etc.
However, you may have a function which is called randomPassword(), which generates a random password from numbers and letter.
This randomPassword() function doesn't need the database object and therefore, an already initialised database connection in the object scope would be wasteful.
It would be better only to create the new database object in methods that required it.
In addition, in my application, I don't create a new database connection each time I used new database. Instead, I've opted for a singleton PDO database object which keeps the connection active.
I can then just call the database object statically to retrieve an existing connection. Therefore, if, in the process of running my application I need to have 20 database objects, my application then only returns the same object, and the same connection.
A couple of the options are:
$connection = {my db connection/object};
function PassedIn($connection) { ... }
function PassedByReference(&$connection) { ... }
function UsingGlobal() {
global $connection;
...
}
So, passed in, passed by reference, or using global. I'm thinking in functions that are only used within 1 project that will only have 1 database connection. If there are multiple connections, the definitely passed in or passed by reference.
I'm thining passed by reference is not needed when you are in PHP5 using an object, so then passed in or using global are the 2 possibilities.
The reason I'm asking is because I'm getting tired of always putting in $connection into my function parameters.
I use a Singleton ResourceManager class to handle stuff like DB connections and config settings through a whole app:
class ResourceManager {
private static $DB;
private static $Config;
public static function get($resource, $options = false) {
if (property_exists('ResourceManager', $resource)) {
if (empty(self::$$resource)) {
self::_init_resource($resource, $options);
}
if (!empty(self::$$resource)) {
return self::$$resource;
}
}
return null;
}
private static function _init_resource($resource, $options = null) {
if ($resource == 'DB') {
$dsn = 'mysql:host=localhost';
$username = 'my_username';
$password = 'p4ssw0rd';
try {
self::$DB = new PDO($dsn, $username, $password);
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
} elseif (class_exists($resource) && property_exists('ResourceManager', $resource)) {
self::$$resource = new $resource($options);
}
}
}
And then in functions / objects / where ever:
function doDBThingy() {
$db = ResourceManager::get('DB');
if ($db) {
$stmt = $db->prepare('SELECT * FROM `table`');
etc...
}
}
I use it to store messages, error messages and warnings, as well as global variables. There's an interesting question here on when to actually use this type of class.
Try designing your code in an object-oriented fashion. Methods that use the database should be grouped in a class, and the class instance should contain the database connection as a class variable. That way the database connection is available to the functions that need it, but it's not global.
class MyClass {
protected $_db;
public function __construct($db)
{
$this->_db = $db;
}
public function doSomething()
{
$this->_db->query(...);
}
}
I see that a lot of people have suggested some kind of static variable.
Essentially, there is very little difference between a global variable and a static variable. Except for the syntax, they have exactly the same characteristics. As such, you are gaining nothing at all, by replacing a global variable with a static variable. In most examples, there is a level of decoupling in that the static variable isn't referred directly, but rather through a static method (Eg. a singleton or static registry). While slightly better, this still has the problems of a global scope. If you ever need to use more than one database connection in your application, you're screwed. If you ever want to know which parts of your code has side-effects, you need to manually inspect the implementation. That's not stuff that will make or break your application, but it will make it harder to maintain.
I propose that you chose between one of:
Pass the instance as arguments to the functions that needs it. This is by far the simplest, and it has all the benefits of narrow scope, but it can get rather unwieldy. It is also a source for introducing dependencies, since some parts of your code may end up becoming a middleman. If that happens, go on to ..
Put the instance in the scope of the object, which has the method that needs it. Eg. if the method Foo->doStuff() needs a database connection, pass it in Foo's constructor and set it as a protected instance variable on Foo. You can still end up with some of the problems of passing in the method, but it's generally less of a problem with unwieldy constructors, than with methods. If your application gets big enough, you can use a dependency injection container to automate this.
My advice is to avoid global in the bulk of the code - it's dangerous, hard to track and will bite you.
The way that I'd do this is to have a function called getDB() which can either be at class level by way of a constructor injection or static within a common class.
So the code becomes
class SomeClass {
protected $dbc;
public function __construct($db) {
$this->dbc = $db;
}
public function getDB() {
return $this->dbc;
}
function read_something() {
$db = getDB();
$db->query();
}
}
or using a common shared class.
function read_something() {
$db = System::getDB();
$db->query();
}
No matter how much elegant system design you do, there are always a few items that are necessarily global in scope (such as DB, Session, Config), and I prefer to keep these as static methods in my System class.
Having each class require a connection via the constructor is the best way of doing this, by best I mean most reliable and isolated.
However be aware that using a common shared class to do this can impact on the ability to isolate fully the objects using it and also the ability to perform unit tests on these objects.
None of the above.
All the mysql functions take the database connection argument optionally. If you leave that argument out, the last connection by mysql_connect() is assumed.
function usingFunc() {
$connection = getConnection();
...
}
function getConnection() {
static $connectionObject = null;
if ($connectionObject == null) {
$connectionObject = connectFoo("whatever","connection","method","you","choose");
}
return $connectionObject;
}
This way, the static $connectionObject is preserved between getConnection calls.