I'm including the MySQLi connection file in the constructor of a PHP class. Since I need to reach the connect variable in methods in this class I need to make the variable global. I always heard global variables are bad. So I wonder, is this the only/best way to deal with this?
class CheckUser {
function __construct() {
require_once('mysqli.php');
}
function checkEmail($email) {
// sql code here
}
}
That's just a meme. (And dependency injection is coming right up...)
Your connection handle is a central resource. Use it as such. A global variable is perfectly fine and the intended langauge construct for that. It makes sense as long as you only have one database / connection.
If global variables were bad, we wouldn't have $_GET and $_POST (which are actual global variables).
Should your class (guessing here) be the central access point to database queries, then keeing the handle as simple property is just as cromulent.
function __construct() {
require_once('mysqli.php');
$this->db = $db;
}
Or whatever local variable the mysqli.php script created.
Related
I've ran into an issue with user already has more than 'max_user_connections' active connections
This happens because I use functions for the website functionality, each function contains a
$mysqli = connect();
Though at the same time, each function closes the mysqli at the end of function
mysqli_close($mysqli);
I do not want to include $mysqli as a parameter of the function, as the function is dynamic and would be tiresome to include it with each function call.
the connect() function just contains:
$mysqli = new mysqli(...);
return $mysqli;
I believe the error is thrown because the function sometimes calls itself for different executions, based on user input and pre-requisites... even though the mysqli is closed at the end of the function...
I'd like to know if there is a way of re-using a $mysqli connection sort of like in a global way...
I'm not sure whether I've explained myself fully so if you need some more information please leave a comment.
The proper way to reuse the same object across multiple functions/classes is to use dependency injection. Together with DI container, it can take care of providing the necessary dependencies to your functions leaving them clean.
The principle of clean code demands that your functions do not have side effects and they only do what their name states. This means that you should never be using globals in your functions as that would be causing side effects. The proper way to provide data without side effects to your function is via parameters. A connection to the database is the data that is required by your function.
If your code will be used as some kind of public library, it's even more reason to keep it clean. A function cannot have surprising behaviour. The best way to reduce surprises is by having a clear function signature. This means that all dependencies are listed as parameters with their correct types, the function cannot take dynamic arguments, and the return type must be clearly specified.
When it comes to mysqli connections (or PDO for that matter which you should prefer over mysqli), the connection should only be opened once during the execution of the script. You should never need to close the connection manually.
Here's an example of clean code. Let's imagine that you need to save bookings in the database. You create a service in your model:
<?php
class BookingService
{
public function __construct(protected mysqli $mysqli)
{
}
public function saveBooking(Booking $booking)
{
$stmt = $this->mysqli->prepare('INSERT INTO bookings (date, surname) VALUES (?,?)');
$stmt->execute([$booking->getDate(), $booking->getSurname()]);
}
}
Then in your controller, you just use your service as a dependency:
class BookingController
{
public function __construct(protected BookingService $bookingService)
{
}
public function index(Request $request)
{
$boooking = new Booking($request->get('date'), $request->get('surname'));
$this->bookingService->saveBooking($boooking);
}
}
Your DI container takes care of instantiating the mysqli and BookingService class. You can only create value objects in your controller. The necessary data is passed via parameters. This makes for a very clean and understandable code. Everyone knows what each function does, there are no surprises and everything has type specified.
There are a number of techniques to instantiate a variable only once. This is an anti-solution. Please do not use solutions listed here!
Static variable
If you only want a variable to be instantiated the first time the function is called, you can use a static variable.
function foo(){
static $mysqli;
if ($mysqli === null) {
$mysqli = connect();
}
// call the same function in recursive mode and the same connection will be reused
foo();
// do not close the connection manually!
}
This is a bad solution because your function fetches the dependency manually. You should not create functions that have side effects or multiple objectives. A function that connects should not be called from within a function that does something else. This leads to nightmarish code, which is the reason why you are having this problem now.
Using singleton
Singletons are bad for testing and for code readability. Anytime you need to change the dependency, you need to change all the places where the singleton is used. For a better explanation of why they are bad see What are drawbacks or disadvantages of singleton pattern?
Using globals
Globals are very bad for code maintainability. They are the bane of programmers since forever. It's precisely the reason why we have encapsulation and dependency injection.
Using a global would be very similar to using a static variable, except that the side effect is now global.
function foo(){
// declare a variable as global.
// this will instantiate the variable to null if it doesn't exist as a global yet
global $mysqli;
// if it's null, connect
if ($mysqli === null) {
$mysqli = connect();
}
// call the same function in recursive mode and the same connection will be reused
foo();
// do not close the connection manually!
// but if you must close the connection, just set the variable back to null
}
Do not use any of the above solutions! These are examples of bad unmaintainable spaghetti code. A programmer's nightmare. This answer is only supposed to be a warning of what not to do!
I'm planning to use a PHP PDO wrapper class from here: http://www.imavex.com/php-pdo-wrapper-class/
I initialized the class with:
$db = new db("mysql:host=$sitedbHost;port=3306;dbname=$sitedbName", "$sitedbUser", "$sitedbPass");
The problem is, that I don't like the idea to make global $db on every function on my other classes like this:
class User
{
function getUserDomains($user_id)
{
global $db;
return $db->select("domains");
}
}
Any help will be highly appreciated.
If you class requires it in order to work, you can inject it in the constructor:
class User {
public function __construct(Database $db) {
$this->db = $db;
}
}
You can then access the database object from $this->db. (Note, I assumed $db is an instance of the Database class. Change it as appropriate).
Here is something for you:
Check new PDO Class Wrapper on GitHub
I don't like the idea to make global $db on every function on my other classes
Well, make it global in constructor only (or pass it as a parameter), and then use as a class variable,
return $this->db->select("domains");
Honestly, you can't avoid passing $db to the function somehow. There is no magic. Whatever fashionable way you choose, you'll end up with setting your $db variable this way or another, no matter how it's called, "dependence injection", "global" or "use the Force, Luke".
I'd vote for global as it's plain and simple.
By the way, this framework is inflexible and insecure. Better use safeMysql as it's way more secure and flexible
I am working on a website with php/mysql.
I have 3 files config.php, utils.php and member.php. code of the files are as below,
config.php - $objPath->docrootlibs is fine, I am sure there is no problem with this.
/* Other library files & their object */
require($objPath->docrootlibs.'/utils.php');
$objUtils = new utils();
require($objPath->docrootlibs.'/member.php');
$objMember = new member();
utils.php
class utils{
function getCurrentDateTimeForMySQL(){
return date("Y-m-d H:i:s");
}
}
members.php
class member{
var $userid;
var $username;
function __construct(){
$this->lastactivity = $objUtils->getCurrentDateTimeForMySQL();
}
}
Now when I am including the config.php inside a page home.php with simple php include statement and running that page then it gives me following error.
Notice: Undefined variable: objUtils in D:\wamp\www\site\libs\member.php on line 17
Fatal error: Call to a member function getCurrentDateTimeForMySQL() on a non-object in D:\wamp\www\site\libs\member.php on line 17
Line numbers in error above are different, I just copied the specific part from the code here.
I am not understanding why its giving error, because objects of utils class is defined on config page before including the member class. It should detect that object.
Please check and help me to understand and correct this error.
Thanks!
One Solution
Unlike JavaScript PHP will not bubble up through scopes, which means
public function __construct(){
$this->lastactivity = $objUtils->getCurrentDateTimeForMySQL();
}
does not know what $objUtils is, because there is no such object defined in the local scope. This means, you have to make the object available inside that scope. The cleanest and most maintainable way to do that is to inject the utils instance to the member instance, e.g.
public function __construct($utils){
$this->lastactivity = $utils->getCurrentDateTimeForMySQL();
}
However, since you seem to be using that value on construction only anyway, there is no reason why your member instance has to know how to use the utils object. So why not just insert the actual value right from the start, e.g.
public function __construct($lastActivity){
$this->lastactivity = $lastActivity;
}
// then do
$utils = new utils();
$member = new member($utils->getCurrentDateTimeForMySQL());
On globals
You definitely do not want to use the global keyword or static methods. Both couple back to the global scope. This means you can no longer use the member class without the global scope. This makes maintaining, reusing, refactoring and testing harder. OOP is about encapsulation and by reaching out from the class to the global scope you are breaking that encapsulation. Use Dependency Injection as shown above instead.
Apart from that, using globals will also make your code harder to read. A developer looking at the ctor signature of member is likely to assume there is nothing else to do than just call new member. That's a lie, because she also has to setup the utils instance. In other words, you are hiding dependencies. The developer has to look at the actual code to understand what's going on. Thus, make dependencies explicit.
Some more resources:
http://c2.com/cgi/wiki?GlobalVariablesAreBad
http://misko.hevery.com/code-reviewers-guide/flaw-brittle-global-state-singletons/
EDITs after comments
If you really need that utils object, inject the instance and assign it to a property inside the member instance in the ctor. Then you can access it with $this->utils->foo() from anywhere else inside the member instance.
However, Utility classes are almost always a sign of bad design. It is much more likely that they should be broken apart and divided into/onto other objects. Try to find out the reponsibilities. Maybe Member should not use Utils, but Utils should be something else that uses Members.
Out of curiosity, why do you need a utility method for MySql anyway? If you use a Timestamp column in MySql for lastActivity, it will automatically update whenever the row is updated. I am assuming you are setting the lastActivity and then store the member data?
Regarding performance: you should not bother about performance. Write readable and maintainable code first and foremost. If you think your performance is not good enough, profile the application with XDebug to see what is really making an impact.
As another comment states, use dependency injection. Insert the utilities object into the constructor. Do not introduce variables over the global scope, especially between different files. This gets very confusing and creates a mandatory order of some file includes.
class member {
...
public function __construct(utils $objUtils) {
$this->objUtils = $objUtils;
...
}
}
In calling code:
$member = new member(new utils);
As an aside, I find it humorous that you have a macro with a name that is longer than the operation it performs.
As another aside, do you need a utilities class? Can the utilities just be functions?
It sounds like config.php is in the global scope. You need to use the global keyword when using $objUtils
function __construct(){
global $objUtils;
$this->lastactivity = $objUtils->getCurrentDateTimeForMySQL();
}
Since your getCurrentDateForMySQL doesn't depend on anything else inside your utils object, why not make it a static function? That way you can turn your member() method into:
function __construct(){
$this->lastactivity = utils::getCurrentDateTimeForMySQL();
}
inside of a function i have a $connection var what obviously stores my connection to mysql,
how can i call that var from inside other functions to save me having to paste the $connection var inside of every function that requires this var?
i have tried global to no avail.
many thanks
You could use the old global keyword.
function a() {
global $connection;
}
Or you could throw it in $GLOBALS (this will help you get it out of the function defined it in).
Neither of them are too pretty.
Or you could pass in the $connection as an argument.
The most common way of dealing with a database connection is to have its creation handled by a singleton pattern, or have a base class with OO that has a $this->db available, that all your other classes can inherit from.
Pass the connection as a parameter to the functions that need it. It keeps your code clean and re-usable.
Another solution would be to use a class and make the connection a class variable. You will just use $this->connection every time you need this, but this is not really a solution if you already have a lot of code written in a lot of files.
Declare the variable outside the function, then make it accessible inside each function you need it by using the global keyword.
$globalName = "Zoe";
function sayHello() {
$localName = "Harry";
echo "Hello, $localName!";
global $globalName;
echo "Hello, $globalName!";
}
sayHello();
stolen from http://www.elated.com/articles/php-variable-scope-all-you-need-to-know/
I have a class Page that creates an instance of DB, which is named $db.
In the __construct() of Page, I create the new $db object and I pull a bunch of config data from a file.
Now the DB class has a method _connectToDB() which (attempts) to connect to the database.
Is there a way in the DB class to call the parent class's config array? I don't want to make global variables if I don't have to and I don't want to grab the config data twice.
Pseudo code might look something like this...
$dbUsername = get_calling_class_vars(configArray['dbUserName']);
I find that it's often easier to initialise all the "important" objects close to whatever variables they need to know. You could try it this way:
/* Code to get config variables here */
$DB = new DB($config);
/* You might want to delete the database password from $config here */
$Page = new Page($config, $DB);
Doing it this way means you can also do type-checking on the database object if you want to:
class Page {
function __construct(array $config, DBClass $db) { }
}
You can use static if you want to share variables without passing these:
class page{
static $configArray = [];
function doWhatever(){
$db = new DB();
$db->connectToDB();
}
}
class DB{
function connectToDB(){
$dbUsername = page::$configArray['dbUserName'];
}
}
In this case makes sense to have those data as static, because even if you have a multiple instances of the page class, the config parameters should always be the same.
Anyway I think that could be better to construct and keep the $configArray only in the DB class. If you want to call it from outside you can use the same static logic.
Why not pass the config parameters to the connectToDb function or pass the config data to the constructor of the DB class.
And to directory answer the question: you don't know anything about the outside calling context in your current context.
See debug_backtrace() to get information about calling classes or objects.
Then see Reflection to get more information on the properties of a given class or object.
edit: But for what it's worth, I'd also recommend passing the specific parameters you need. Referencing the caller's data probably constitutes Content Coupling.
You can pass the child a reference to the parent. For example:
class Parent {
function __construct() {
$this->myChild = new Child($this);
}
public function doSomething() {}
}
class Child {
function __construct(Parent $parent) {
$parent->doSomething()
}
}
You may find this odd, since you're still in the parent's constructor, and thus your parent object isn't fully constructed yet. But you can still use $this as a reference to yourself, even in the constructor. You just need to be careful that your child doesn't refer to things in the parent that haven't been initialized yet.
In general there is no easy way to do this. but as a general design issue i can see why your avoid global variables, but in the case of application wide configuration it is perfectly reasonable to have global access to the properties.
you can either make your config data global or just pass the needed properties to the db object initialization.