What is the correct abstraction/structure to save this object to storage?

Question

I have an object called SecurityServer.

It is created using SecurityServerFactory.

I need to serialize SecurityServer to disk/hardware token/ or some other storage.

Which is more correct:

• securityServerInstance.Save()
• StorageAbstract.SaveServer(securityServerInstance);
• Both?
• Neither? Use injection?

I have a feeling I need to understand domain driven design, but I'm self taught at this point and am starting to finally "get it"

Answer 1

If you use StorageAbstract.SaveServer(securityServerInstance); then StorageAbstract will need to be able to access everything inside a SecurityServer object that needs to be serialized. This could be a problem if there is internal state that needs to be saved but is not - and possibly should not be - accessible outside the of SecurityServer. If you don't want to worry about that, then maybe have the object save itself.

Answer 2

In the context of DDD (Domain Driven Design), the only consistent answer is to use a "Repository": rep.save(securityServerInstance), where rep is an instance of SecurityServerRepository.

Answer 3

You were are faced with two choices: 1. Expose private members so an outside class can access those members 2. Make the object save itself

I suggest a third option: Use the visitor design pattern and create a visitor whose purpose is to serialize the object.

This helps your Security server have less responsibilities.

Think of another example, such as making a textual report from the class. This report needs to include data only visible to the security server. Would you also like to implement that method within the security server?

Using the visitor design pattern would help you to reduce code within the class and separate responsibilities