Should sub-objects be fetched in the Model or the Model Mapper?

问题

This is a follow-up to my previous question: Should dependent rows be fetched in the Model or the Controller?.

Let's say that a Patron can check out Books. If, given a Patron object, where and how should the Books they have checked out be fetched?

Here are some possibilities I've considered:

• In the Patron Model, add a getBooks method
• When a Patron is instantiated, automatically get its books and store it as the books property
• Create a method in the PatronMapper called getBooks that takes a Patron ID

What would you recommend? Thank you,

回答1:

I suggest you to go with:

When a Patron is instantiated, automatically get its books and store it as the books property

This way you don't have to manually worry about it

来源：https://stackoverflow.com/questions/6237817/should-sub-objects-be-fetched-in-the-model-or-the-model-mapper