PHP classes: Need help to inherit two classes - php

I need help in designing my PHP classes where I need to extend from multiple classes.
I have a general class, Pagination.php that does all sort of pagination and sorting. All other classes will use this for pagination.
To make my life easier, I made a class generator that generates a class from MySQL table. All the properties, getters, setters and common methods are created automatically, which really saves time and money.
As an example, class Staff_Base in Staff_Base.php is generated automatically from SQL table t_staff.
Since class Staff_Base is automatically generated from SQL table, any 'custom' methods / properties are located in another class that extends Staff_Base.php. (So that whenever a new field is added, I can simply regenerate Staff_Base class and overwrite in Staff_Base.php).
So I have class Staff.php that extends Staff_Base.php.
The problem is, Staff.php also needs to extend another class, Pagination.php.
(The current workaround is to put methods in Pagination.php into every class. This is really troublesome whenever I make changes to the pagination/sorting methods.)
How do I do this?
What is the best design pattern to achieve this?
I know common suggestions to restructure my classes, but I really think hard of other workaround/solution. Also, I may also need to extend other classes than Pagination.php.
Thanks!

Can you have your generated Staff_Base class inherit from Pagination? Or does Staff_Base already inherit from another base class (that you do not have control over)...
Sounds like either Doctrine or Propel, I do not recall which uses the *_Base class system.
My suggestion would be to rewrite pagination to be able to be used by your entity classes instead of requiring your entity classes to extend it.

So if I am reading what you wrote correctly, since you can't inherit from 2 classes you are duplicating paginate into every class you have.
Class stacking is a solution. One of the first things I googled.

I would recommend changing your Staff_Base.php generator to make that class extend Pagination by default. That way Staff extends Staff_Base, and Staff_Base extends Pagination. I think that's probably the cleanest (and most object-oriented) way of getting the results you want.

you cant, multiple inheritance is not supported in php, but if you do a google search on this topic you can find some workarounds...

It sounds like you're mixing things up here. A class (such as a Staff class) is used to represent a single entity. Eg:
$john = new Staff('John');
How exactly does the paging fit into this? Being page-able (paginatable?) sounds like a property of whatever it is that allows access to these Staff entities, not of the entity itself. That way, the way is clear for each type of Staff class you create to inherit from the base class.
So, what I believe would be the solution you need:
A Staff class (Staff_Base, and its graph of children)
A Staff Data Access Object (DAO\Staff would be a nice name, if you're using namespaces)
An Interface, to signal to the world that a DAO can be paged
Import to note is that there is no direct inheritance between the DAO class and the Staff class. You can still generate the Staff_Base class based on its properties in the database, and extend from there... as long as you don't include the actual data access in that class.
The code using this would then look something like this:
<?php
$staffDao = new DAO\Staff;
$staffMembers = $staffDao->getPagedResult($start, $amount);
?>
Edited to emphasize that the inheritance structure should be separate from the actual retrieval

Well, you might already know that PHP doesn't support multiple inheritance. One way around might be using Interfaces instead of superclasses, although, if the logic is identical for each implementing of the interface, this might become tedious. How about writing a code generator, that simply injects the methods to each class? You seem to already do that on the "common methods".
Oh, and using getters and setters (as they are used in e.g. Java) in PHP is considered not a good idea. Objects are slow as they are, so using public fields is considered the norm.
Edit: Then there's the __call()-hack, which could recognize the methods that actually reside in your other classes, and call them manually.

Related

My models all tend to look the same

I've noticed that all my models look very similar. Most of them tend to follow a pattern where they are collections of methods containing active record code that are just slight variations on one another. Here is an example:
class Site extends CI_Model {
public function get_site_by_id($id)
{
// Active record code to get site by id
}
public function get_sites_by_user_id($user_id)
{
// ...
}
// ...
public function get_site_by_user_id_and_url_string($user_id, $url_string)
{
// ...
}
// Non active record methods and business logic
// ...
}
This approach has worked fine for me but I'm wondering if there is a more elegant solution. It just doesn't seem right to me that I should have to create a new method every time I need to look up data in a new way. Is this common practice or am I missing a way to refactor this?
Strictly following your request, you could add an intermediate class between the main model class (CI_Model) and your class (Site), something like
class MyCommonMethodsClass extends CI_Model {
}
and you would extend it in your classes (Site), while putting the common code on it. That would work and could be somehow'elegant'. In fact at the end you would end up adding your basic crud, site adapted actions, to it.
Now, if that's 'clean', that's another thing. Again, strictly speaking the model does that. It takes care of common and 'advanced' getters. And yes, they almost always have the tendency to have the same code all around your website. The problem is that, although that looks nice in your code (less code) you're technically sacrificing abstraction between your business logic and the db. Are you a model purist or practical one ?
I think this is matter of opinion but I think best practice is to create some sort of Create, Retrieve, Update, Delete (CRUD) model which does many basic SQL functions like GetID, UpdateByID, GetById and so on.
CRUD models can only go so far in helping you with more modular queries. But it makes sense to call a function called GetId and pass it some parameters than to have different functions for each table.
As I say though, CRUD's can only go so far. For example it would make sense to have a function that queries a database users table to check if a user has verified and username & password match. As this is a unique and not an abstract function, it should have it's own function defined.
Also as a best practice, Logic and Database access should never be mixed in the same file.
It is common practice to have different methods to handle getting your data like that. The Single Responsibility Principal states that every object should only do one thing, by making multiple methods that get very specific data you are creating very maintainable and easy to debug code.
If you have multiple classes that are providing essentially the same functionality, then this would suggest that there may be something wrong with your class hierarchy (a so-called "code smell"). If they have similar interactions then that suggests that they are related in some way. If that's the case then the chances are they should all be inheriting from a common superclass that implements the functionality common to all your subclasses, with each subclass simply specializing the generalized functionality of the superclass.
The advantages of this approach are:
You're not repeating work (SPOT, DRY)
Code that interacts with the classes can be written in a more general way and can handle any object that inherits from the superclass (substitution)
I do not think there is any thing wrong with creating an 'base' model class to extend you other models by. If it is solid and well tested, it can make you life easier. What is the point of creating the same CRUD functions over and over again?
Another benefit of doing it is that you can have a base development repository that you clone to start all new projects.
If you need an example of how to do this then look at a question I previously asked.
You can also do the same with your controllers.

CModel subclass in yii

I am a 4 days old yii fan and I like it so much.
I have a special database table that can't be used by CActiveRecord directly. My solution is to subclass CModel to have my own logic for listing, creating, saving and deleting records. My new CModel subclass cant not instantiated; it seems that CModel requires more methods to be defined to allow creating an instance from it.
My question is: Is this the right approach to go or there are better ways? If yes, what are the missing methods to define to make my new class complete; not abstract
Thanks
I usually create my own classes to handle the so called 'logic' of the webapp that I'm building.
I place it in another folder (usually the logics folder) and auto import the directory from the config. The logic classes doesn't subclass from any Model
public class ProfitLogic { ... }
where inside the class(es) I implement functions that instantiates and use any ActiveRecord(s) that I need.
The reasoning for this is that when prototyping I often refine my database design, and I need to regenerate the ActiveRecords again :p
Your approach is fine generally speaking, and would be fine even if you were not "forced" to adopt it. I use a CActiveRecord subclass as the base for my models to provide additional custom functionality.
As for your other question, you only need to implement attributeNames() to be able to instantiate objects of your class.
However, why do you not subclass CActiveRecord directly instead of CModel? You can still override any and all methods you choose to. Is your database so dramatically different from the usual schemas that you won't be able to reuse any of the logic?
I'm fairly new to Yii as well, but have found that extending CForm, as in the default ContactForm model can be useful.
Not the best for having lots of heavy business logic, but it touches on your point of breaking out of the typical workflow.

Extending a class with common functionality

I have three classes which basically do very similar things;
Store a record of an uploaded file.
Move and upload the file.
Set the status of the record to active or revoked.
One of the classes has an additional update method. Each class references a different table in the database because although some of the fields are common, there are a couple of fields extra in some of the tables.
As quite a lot of the functionality is common I think it may be best to extend a base class rather than duplicating a lot of the functionality.
My only quarrel is the construct function on the base class. As some of the fields in each table are additional I'm concerned this will prevent a base class.
I have thought of using an abstract class as this will allow me to extend on functionality whilst maintaining most of the things in one place. But it's the problem with the construct. Can I have an abstract class with no construct?
Any ideas?
If I understand you: You can have any class without __construct(). And you can always overwrite every method (except methods, that are declared as final) of a parent class in a child class.
I am sorry but I guess I do not completely understand your question. Anyway in inherited class you can always override the constructor and within it invoke the superclass constructor plus further stuff if needed.

Having the option of customized classes but a unified class name

Suppose you are building a web application that is going to be a packaged product one day, one that users will want to be able to extend and customize.
It comes with a core library consisting of PHP files containing classes:
/library/
/library/frontend.class.php
/library/filesystem.class.php
/library/backend.class.php
Now, suppose you want to keep a clean core that users can't patch. Still, you want the user to be able to customize every nut and bolt if need be.
My current idea is to create an autoloading mechanism that, when a class is instantiated, first loads the core include:
/library/frontend.class.php
then, it switches to the user directory and looks whether there is an include of the same name:
/user/library/frontend.class.php
if one exists, it includes that as well.
Obviously, the user include must contain a class definition that extends the definition in the core include.
Now my question is, how would I instantiate such a class? After all, I can always be sure there is a definition of:
class frontend_core
but I can not be sure there is a
class frontend_user extends frontend_core
However, I would like to be able to rely on, and instantiate, one class name, regardless of whether there was a custom extension to the class or not.
Is there a clever way, idea, or pattern how to achieve this?
Of course, I could write a simple factory helper function that looks for the user class first and then for the core class and returns an initialized object, but I would really like to keep this as clean and simple as possible, because as I said, it is going to be a packaged product.
I am looking for a smart trick or pattern that uses as little code, and introduces as little new functionality, as possible.
Why don't you follow the approach as used by Propel? You generate your base classes and already provide an empty User class (extending the base class) where your users can put their overrides/specific implementation details, and in your code you always refer to the User classes. So basically you just use the inverse of the logic you described.
If the explanation above isn't clear, check out http://propel.phpdb.org/trac/wiki/Users/Documentation/1.4/QuickStart#a6.UsingtheGeneratedSQLandOMFiles and generate code for a small database. The base classes are in the om folder, the (by default empty) user classes are in the root folder.
I would implement hooks in the core, so users dont have to hack the core, but are still able to extend the core using hooks
I'd go with using the constructor of the core class to determine the user class to load, and then implement a factory method in the core class to generate instances of the user class. By making the constructor of the user class protected, and having the user class extend the core class you can be sure that code elsewhere cannot instantiate the user class.
C.
I think it's more complicated with a single filename when you want to use inheritance as well. Basically class user_frontend extends core_frontend has to know where to find both classes. Both must be included.
If you just want to do new Frontend you could use PHP5.3's class_alias to point Frontend to the main class to use. Below 5.3. you could use a ServiceFinder, that knows how to map Service Names to Classes and then get the Frontend with $service->get('frontend') or use a Dependency Injection framework.
Edit I removed the Loader code given before, because it was suffering from exactly this problem.
You could have a loader class that will decide which class to instance:
Loader::instance()->load('Frontend')

Correct Implementation of Virtual Functions in PHP?

at my working place (php only) we have a base class for database abstraction. When you want to add a new database table to the base layer, you have to create a subclass of this base class and override some methods to define individual behaviour for using this table. The normal behaviour should stay the same.
Now I have seen many new programmers at our company, who just override the method for the default behaviour. Some are so "nice" to put in all the default behaviour and just add there individual stuff where they like it, others kill themself trying to use the baseclass and their inheritor.
My first thought to solve this problem, was thinking about abstract methods that should be overriden by inheriting classes. But beside other arguments against abstract methods, "abstract" just does not show why the baseclass can't be used by its own and why these function should be overriden.
After some googling around I didn't find a good answer to implementing "real" virtual functions in php (just that there is a virtual function, that nearly kills all hope of a concrete implementation).
So, what would you do with this matter?
In PHP all public and protected functions are "virtual". You can prevent functions from being overriden by prepending the final keyword. (Or by making them private, but this is probably a bad idea).
In the design of the baseclass I would think of behaviors that subclasses would want to affect.
I would for example create empty functions like before_update() and after_insert().
function after_insert() {
// Virtual
}
Which the baseclass will call when an update/insert event occurs.
Maybe an is_valid() function which always returns true in the baseclass, and use the commentblock to describe what the consequences are when a subclass return false.
Hopefully this would give you some inspiration.
You can always use the "final" keyword to prevent some of the classes functions from being overridden if people are using the class in the wrong way.
It sounds to me like they are unable to acheive certain functionality hence overriding the methods. You may need to take a look at the design of your classes.
Without an example of the implementation of your base class, it's hard to give concrete info. But a few things come to mind:
Database abstraction is complex stuff to begin with. I understand that you want to keep it lean, clean and mean, but I think it's pretty darn difficult. You really have to take a thorough look at the specs of different DB engines to see what parts are general and what parts need specialization. Also; are you sure you don't have DB abstraction mixed up with the Table Data Gateway pattern, as you are talking about adding DB tables by extending the base class?
The methods of your current base class might be doing too much and/or are not general enough to begin with, if the extended classes are bending over backwards too keep it clean. Maybe you should break the base class interface methods up in smaller protected methods that are general enough to be reused in the overriding methods of the extended classes? Or vice versa: maybe you should have hooks to overridable methods in your interface methods.
Following from point 2: What's wrong with having an abstract class with some general implemented methods, and let your vanilla class (your base class) and other classes inherit from that?
Lastly, maybe you should just enforce an interface to be implemented, in stead of extending the base class?

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