PHP OOP: retrieve data from database

Question

I'm pretty new to OOP (and also in PHP programming), and I have some troubles using objects and interfacing them with db data (MySql in my case, but this is irrelevant).

I have on the DB a table USERS. I declared a class User in the PHP code, with the various properties and methods I need. The problem is interfacing this thing to db.
I put code to retrieve data from the db in the constructor, so when I need to work on a specific user, I simply write $user = new User($user_id); and start working with the object. When I've done I call a method on the object to save data on db, and this works pretty well.

The problem arise when I need data about many users in a single page, as in showing the complete list of users. With this approach, when I need the list of users, I have to instantiate all the objects, and this causes the code to make too many queries of the type SELECT * FROM users WHERE user_id = ..., instead than a single query such as SELECT Only_needed_fields FROM users WHERE 1 LIMIT 20 as I would've done in procedural code.

Which is the correct OOP approach to such a problem? Which is the good-practise alternative to retrieving data in the constructor?

Notice Please, don't suggest using frameworks of any kind - I'd like learn pure OOP PHP before using abstraction layers -

Dan · Accepted Answer · 2011-07-24 14:11:26Z

2

Your problem is that you are not seperating the layers of your application. What you should do is have a factory class instantiating your users that handles the database calls and let the user class only handle the business logic. This will also contribute to the testability of your code.

Your factory class could have two methods. One for loading a single user and instantiating it and another for loading a set of users.

answered Jul 24, 2011 at 14:11

Dan

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10 Comments

afuzzyllama Over a year ago

Well said. Also, I'd say using a singleton object structure for your DB is the way to go.

marcello Over a year ago

Hm, so when I need a user, I call something like Factory::GetUserById($id) or Factory::GetAllUsers() etc..., and let the User constructor do not initialize parameters? Seems a good idea, I didn't think of it, thanks a lot. (it seems quite difficult to abandon procedural paradigms :-))

Dan Over a year ago

Thanks. I would disagree on the singleton pattern though as it makes your code harder to test. youtube.com/watch?v=-FRm3VPhseI You would rather want to pass every dependency using a constructor or method than altering the global state.

Dan Over a year ago

marcello: Yes, your user constructor instead just accepts the parameters that make up the actual user instead of having to take the burden of getting it's own data. You will have the added benefit of being able to mock-up other structures should you want to test your code with phpUnit for example.

marcello Over a year ago

@afullyllama why singleton? sorry but I don't unserstand... I don't have to be sure having only one object instantiated, it is not simpler to just declare static methods? (perhaps singleton could be useful for the database wrapper class, but this is another story)

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Steve-o · Accepted Answer · 2011-07-24 14:12:03Z

2

A factory method is always plausible, then you can implement an optimised common query:

list($one, $two) = User::GetMultiple (array( 1, 2 ));

Translating into

SELECT * FROM users WHERE user_id IN ( 1, 2 );

answered Jul 24, 2011 at 14:12

Steve-o

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