Business Objects - Containers or functional? [closed]

Question

Where I work, we've gone back and forth on this subject a number of times and are looking for a sanity check. Here's the question: Should Business Objects be data containers (more like DTOs) or should they also contain logic that can perform some functionality on that object.

Example - Take a customer object, it probably contains some common properties (Name, Id, etc), should that customer object also include functions (Save, Calc, etc.)?

One line of reasoning says separate the object from the functionality (single responsibility principal) and put the functionality in a Business Logic layer or object.

The other line of reasoning says, no, if I have a customer object I just want to call Customer.Save and be done with it. Why do I need to know about how to save a customer if I'm consuming the object?

Our last two projects have had the objects separated from the functionality, but the debate has been raised again on a new project. Which makes more sense?

EDIT

These results are very similar to our debates. One vote to one side or another completely changes the direction. Does anyone else want to add their 2 cents?

EDIT

Eventhough the answer sampling is small, it appears that the majority believe that functionality in a business object is acceptable as long as it is simple but persistence is best placed in a separate class/layer. We'll give this a try. Thanks for everyone's input...

Answer 1

Objects are state and behavior together. If an object has sensible behavior (e.g., calculating age for a Person from their birth date, or a total tax for an Invoice), by all means add it. Business objects that are nothing more than DTOs are termed an "anemic domain model." I don't think it's a design requirement.

Persistence is a special kind of behavior. What I'm calling "sensible" is business behavior. A business object need not know that it's persistent. I'd say that a DAO can keep persistence separate from business behavior. I don't put "save" in the "sensible" category.