[tsimionescu]

Passing dependencies in the constructor is the only acceptable way of having stateful dependencies (like a database or some external services). I am assuming you are against passing things like Math libraries by creating an instance, which I would agree with.

The only reason dependency injection gets a bad rep is magical frameworks which obscure the actual wiring and end up causing bigger problems.

[cryptica]

I also would not pass in a database client instance. I would pass in the config for the database client though.

I think that the class which ineteracts with the database directly via the client should be tightly coupled to the database client. It's not very often that you change database and when you do, you can just swap out that entire class completely. Classes which interact with the database should expose simple interfaces for performing actions against the database and those wrappers should be replaceable.

[tsimionescu]

Then how would you handle connection pooling, if every class which interacts with the database has its own instance of the database client?