Question

I know that Singleton pattern is bad because it uses global state. But in most applications, you need to have a single instance of a class, like a database connection.
So I designed my Database object without using the singleton pattern but I instanciate it only once.

My question is, how can I access my object in the low level classes (deep in the object graph) without passing it all over the place?

Let’s say I have an application controller which instanciates (ask a factory to instanciate it actually) a page controller which instaciates a User model which requires the database object.

Neither my app controller nor my page controller need to know about the database object but the User class does. How am I suppose to pass the object to it?

Thanks for your time!

Answer 1

Consider using a global container:

• You register the objects that are indeed relevant to the several subsystems of the application.
• You then request that container those objects.

This approach is very popular in dependency injection frameworks (see Symfony DI, Yadif).