PHP OOP-Php对象扩展了Mysql Object =多个Mysql连接？

Question

I'm currently working on a Shopping Cart in which I use a custom Mysql Class to send query to the db.

On this project, I plan to extends this Mysql Class for each Object that I will use : Category, Product, Shopping Cart.

If I create a class like this one:

class Catalog_Categories extends Mysql{}

And then another one like this:

class Catalog_Products extends Mysql{}

Are those classes using the same Mysql Object to connect on DB or are they using 2 separate connections?

I'm a little bit lost.

Thanks!

Carl.

Answer 1

That depends on how your Mysql class is written. If you write it using a Singleton pattern, it will maintain one database instance. You could write it as a Factory pattern and have it generate a new instance for each object that uses it. There are many other patterns and possibilities available so it all just depends on how you want it to work and how you wrote the custom Mysql class.

Answer 2

Assuming that you are creating a database connection in your Mysql class, every object your create of any of the extending classes, will create a new DB connection.

There are several ways to avoid this, for example, you can create one global connection to your database and pass that connection to the constructor of your class so that they all will use that same connection.

Answer 3

Are those classes using the same Mysql Object to connect on DB or are they using 2 separate connections?

We cannot answer this question until we see the complete code.

But extending in this case looks like a bad idea. If you cannot say that class A is a class B - then you should prefer composition over inheritance. This means that Catalog_Products should have a reference to mysql object, but shouldn't extend it.

To get you idea when inheritance is justified is class mysql extends database . In this case you can say "mysql is a database", so extension here looks reasonable as long as database class encapsulates the common logic, and mysql class represents more detailed specifics.