I have used object oriented more in java, where a private member cannot be accessed from outsite the class, protected extending access to child classes, default access extending access to packages and public to every class.
How does this work in PHP when using MVC frameworks( I am using CodeIgniter)? Does it mean all methods in models which I will be accessing from Controllers have to be public?
It means the same thing.
There are no friend classes in php, so you cant break private just because you are using a MVC pattern. Note this is true in Java as well.
This isnt really CI specific... but yes. check out: http://www.php.net/manual/en/language.oop5.visibility.php for more info on php method/property visibility.
Related
Smarty allows to access object properties using this syntax in templates:
{$object->property}
But (If I understood this correctly) this is possible only if property visibility is public, otherwise it seems that Smarty won't be able to access it.
In Java I'm used to create objects that have private properties, and I usually read/write these properties in business logic using getters and setters. But, even if I create an object with a private property, I'm able to access it in a jsp using expression language:
${object.property}
This won't happen in Smarty templates, since private properties cannot be accessed this way. So I would have to use a syntax like:
{$object->getProperty()}
Why is that? Why doesn't Smarty get round the problem as jsp EL does?
Reading and writing to private members of object from the outside violates OOP encapsulation principle. If you mark a member of class as private, you expect that no one except the code in the class (or friend functions) can access it.
Keeping as few public members as possible reduces dependencies between different code modules, making your application more flexible. If you can access private member of, let's say your model, your template must know internal implementation of the model. Making changes to your model will cost you a lot of time, because you would need to change your templates as well.
If you have getter and setter of your private member, you are free to change it as you like, template will know nothing.
I have a functionality that need to be shared by a few classes that manage a common aspect of my software. In Java, i would have all theses classes in the same package and the common functionality would be in a protected method in a helper class.
In PHP, protected method mean that you can only use it in sub-classes so my current solution is to make the method protected and have all the classes needing this method to extend the helper class. The problem with my current solution is the fact than you can't inherit multiple classes so lets say i need to helper classes, im ...
So, is there a way to have a method visibility comparable to java protected in PHP? If not, any cleaner way to solve my problem?
It sounds that you are looking to use traits.
http://php.net/manual/en/language.oop5.traits.php
This would let you define your shared protected method and provide to the classes that require it. I would recommend implementing this with an interface so that you can specify that the method provided by the trait has to be there.
PHP only lets you extend one abstract class however you can implement multiple interfaces.
You could try namespaces (5.3) and reference the utility class instead of extending it. This doesn't quite solve the problem but it does help isolate your class. I try to avoid using private methods.
In PHP 5.4 they added traits which kind of allow a class to extend multiple classes. Schleis has already answered with that.
I am learning about modules online and it seems like modules in js and classes in php are very similar. Both group functions together for easier to understand coding. Functions can be declared in both and made public or private. How are they similar in use and how are they different?
Javascript's modules provides some nice features like encapsulation, the private state and even inheritance from other modules. While they provide some of the features of classes, as in PHP, they are not. They try to build on the existing Javascript functonality to emulate classes, hence why the confusion. i.e. they are built to look and feel like classes.
Javascript's modules are instances of an anonymous function assigned to a variable. Therefore they have all the features of a function where their code is executed top to bottom, they have and sometimes use a return statement (in PHP classes no statements can be run directly apart from field definition and assignment) and they even have access to global variables. In PHP, on the other hand a class, or rather it's methods, cannot access a variable that is not in the class itself. In order to access global variables a class method or static function has to explicitly call the variable i.e global $a inorder to import it. In js modules, all global vars are accessible but sometimes one chooses to explicity import them for neater code (function(a){})(imported);
Another important issue is data abstraction. While js modules provide private states for the fields, PHP's classes, just like C++, java, python etc, provide more security to the properties. It allows for base classes using the abstract class and interface keywords whereby class methods and attributes are only defined or structured but not used.
PHP classes also have constructors and destructors, that are called when the class object is initialized and on the last mention used to destroy the object. Granted, you can create functions in modules to run when you want, in PHP on the other hand, functions in the method are only executed when they are called either by the object, the class or other functions.
In classes there are static functions, these can be called without even having an object of the class and run independent of objects, on the other hand in js, everything is an object; which defeats the point of static functions.
They are similar in that: both have inheritance, where you can extend an existing module with a new one, and in PHP you can use extends to inherit from a parent class. They both have private data states preventing external access, they both group and package data and methods, and both are awesome when utilized properly.
I come from a Java background and I am now trying to study PHP for a web project I am doing on the side written in CodeIgniter. Right now I am trying to study how to use CI's models. I am naturally very curious about reading framework code to gain a deeper understanding of how the tools I am using work.
I am really confused as to where the the "$db" in "$this->db" comes from in the Model classes that extend CI_Model come from. I checked the CI_Model class itself but it is not there.
Prior to this I have read the CI_Controller's code and somehow reckon that the although the $this->load->model(....) is not an instance variable ($this->load) with a method model(..._), somehow "it is there" because the constructor instantiates a $this->load instance variable in the constructor (the Loader class found in the core/ folder which has a model(...) function.
But for the $CI_Model I don't see the same thing. Where does the "$this->db" being referenced and when is it loaded?
I've not studied the code hard enought, but I've been using codeigniter for a while, I hope not to say something wrong, but things doesn't work as you guessed. The $db you're looking for is not in the CI_Model superclass (nor in the CI_Controller superclass), but it's a variable declared in the Loader class (system/core/loader.php).
A codeigniter application is designed to work as if it were a giant "superclass", in fact all libraries and models and so on are instantiated using $this (which usually is used in the scope of a class), so when you're loading the db library - and you can do it in your models but also in your controllers (and, if you instanciate the main $CI class in a custom library, also there) - you're in fact referring to a variable create in the loader class, precisely in line 229 (more or less) inside the database method of the CI_Loader class.
I'm not so deep in CI knowledge to give you better details, but if you take a look at the codeigniter.php and loader.php you can get enough insights to underdstand how CI internally works.
If you have other question or something's still not clear just ask ;)
$this->db might be loaded localy in the model/controller: $this->load->library('database') but most likely database library is autoloaded - check: application/config/autoload.php. For the code you should check CI_Loader class like Damien says.
I just noticed this behavior today - weird, I'm pretty sure in java a you can only access protected methods upstream on the inheritance chain since going the other way violates encapsulation.
Was there a reason for this behavior in the language?
I've found it useful when one method defined in the parent only needs a small part of its functionality to change based on the extension class type. You can call an abstract method from within the parent, and it's functionality changes as needed with the definition of that method in the child classes.
I would also add that sibling classes can also access each other's protected properties and methods, as long as they are declared in the parent class (this can be abstract or not).
This is allowable in Java as well. This is probably allowed in Java however, since protected is also considered to be package level scope and not just relegated to access within the inheritance chain.
protected != private