Question

I have the following objects: L1User, L2User, L3User (all inherits from User) and Document.
Every user can create the document but depending on the user type, the document will have a different status. So in case it’s L1User, the document will be created with L1 status and so on:

Solution 1
Please note that after document is created, it will be saved in the database, so it should be natural to have a method create_document(User user) in Document object. In the method body I could check which type is the user and set manually appropriate status. Such approach seems rather not OOP to me.

Solution 2
Ok, so the next approach would be to have all users implement a common method (say create_document(Document doc)) which will set a status associated with the user and save the document in the database. My doubt here is that the document should be saved in it’s own class, not the user.

Solution 3
So the final approach would similar to the above, except that the user will return modified document object to it’s create_document(User user) method and save will be performed there. The definition of the method would be like this:

create_document(User user)
{
   this = user.create_document(this);
   this->save();
}  

It also doesn’t seems right to me…

Can anyone suggest a better approach?

Answer 1

I think that both Solutions 2 and 3 are ok from the OO point of view, since you are properly delegating the status assignment to the user object (contrary to solution 1, whare you are basically doing a switch based on the user type). Whether to choose 2 or 3 is more a matter of personal tastes.

However, I have a doubt: why do you pass a document to a create_document() method? I would go for a message name that best describes what it does. For example, in solution 3 (the one I like the most) I would go for:

Document>>create_document(User user)
{
   this = user.create_document();
   this->save();
}  

and then

L1User>>create_document()
{
return new Document('L1');
}

or

Document>>create_document(User user)
{
   this = new Document()
   this = user.set_document_type(this);
   this->save();
}  

and then

L1User>>set_document_type(document)
{
document.setType('L1');
}

Edit: I kept thinking about this and there is actually a fourth solution. However the following approach works only if the status of a document doesn’t change through its lifetime and you can map the DB field with a getter instead of a property. Since the document already knows the user and the status depends on the user, you can just delegate:

Document>>getStatus()
{
   return this.user.getDocumentStatus();
}  

HTH