示例 Inheritance Cakephp

Question

Im planning to make a website using Cakephp, and one of the 'requerimients' is using inheritance in the database.

The parent Entity pretends to have common properties but most important an id (key attribute) that is passed to its subentities, which of course have their own set of attributes.

Does Cakephp support this feature? If it does, can anybody provide an easy example of using inheritance? (not multiple inheritance btw)

I'll appreciate your answers.

Answer 1

while I don't think it supports it directly you can do that with some Set class magic. one of the most awesome classes around.

http://book.cakephp.org/view/1487/Set

and

http://book.cakephp.org/view/1508/merge

if it is quite simple stuff you are doing, array_merge() will do it for you too

You would easily be able to create a behavior that does this in the afterFind() callback so that its transparently done in one place and all ready for your view just doing a normal $this->Model->find('all') etc

Answer 2

You'll need to implement this behavior via CakePHP's built-in relational mapping (hasOne):

http://book.cakephp.org/#!/view/1039/Associations-Linking-Models-Together

You can then modify the AppModel class and implement an afterFind method (to work with all models) and massage/merge the data.

Answer 3

You might consider using Doctrine as an ORM, which supports inheritance through column aggregation: http://dqminh.com/integrate-doctrine-orm-with-cakephp-part-1

Answer 4

http://bakery.cakephp.org/articles/taylor.luk/2008/10/22/inheritable-behavior-missing-link-of-cake-model

This is a behavior written some time ago - it might be old but it should give you a very good foundation for understanding how to manage STI (single table inheritance) using Cake.

** EDITS **

From the article I linked - which might not be current or working code. I mentioned it as a starting point for you to work out your own behavior code.

The type is inferred by the class type - and the structure you are talking about only applies to the single table inheritance type of setup. Make absolutely sure you are doing the import of the parent class like the examples show. IE:

<?php
    ...
    App::import('Model', 'Person');
    class Manager extends Person
    { 
        ...
    }
?>

Answer 5

I'm new to CakePHP (as in one week's worth of experience) but have run into the same issue. As has been hinted at already here, it seems that composition is the most conventional way of getting toward Model extension (as you mentioned in a comment using Has-A instead of Is-A).

Here's what I'm trying and hoping works for my relatively simple set of use cases:

//'Super Class'
class Log extends AppModel {
     var $name = 'Log';    
}

//'Sub Class'
class SharedLog extends AppModel { 
    var $name = 'SharedLog';
    var $hasOne = 'Log';
    var $validate = array(
        'log_id' => array(
            'logRule-1' => array(
                'rule' => 'notEmpty',  
            ),
            'logRule-2' => array(
                'rule' => 'isUnique',  
            )  
        )
    );
}

I'm hoping this get's close to what one would need a subclass to do. When you explicitly ask for SharedLogs you'll have access to the Log attributes. If you make the request from the perspective of a Log you won't have access to any SharedLog extended attributes (but that makes sense because if you're going through a collection of Logs you wouldn't know which are the super class and which are the sub class).

I think the validate variable is enough to prevent orphans and duplicates in the database.

Speaking of the database, I went out on a limb made it so that the shared_logs table doesn't have an id column and instead uses log_id as its primary key. I'd love to get some feedback on this setup because I'm completely new to the framework and don't have that sixth sense for when code "just feels wrong" in this context.

EDIT: I was just thinking that assuming I'm not completely going about this the wrong way (and I'd like to think I'm not) this solution offers a pretty straight forward way to make an instance of the super class into an instance of the subclass. Since a Log may not be shared until after it is created. This might just make the belabored point that I should have been thinking composition from the beginning.