可休眠的可重用懒加载

Question

Here are some methods I have in my UserRepository class :

// Get a user with all his roles
getWithRoles(Long userId);

// Get a user with all his posts
getWithPosts(Long userId);

// Get a user with all his activities
getWithActivities(Long userId);

// Get a user with all his relations
getWithAllRelations(Long userId);

These methods all have something like bellow to determine the relations to be loaded:

// An example for getWithRoles(Long userId);
criteria.setFetchMode("roles", FetchMode.JOIN);

I did my best to not duplicate codes between these methods but it is still hard to maintain IMO.

Is there a way to avoid this and end up with something like bellow?

userRepo.findOne(userId)
        .withRelation(User_.roles)
        .withRelation(User_.posts);

userRepo.findOne(userId)
        .withRelation(User_.roles)
        .withRelation(User_.activities);

userRepo.findOne(userId)
        .withAllRelations();

I'm basically looking for a way to reuse relations-fetcher methods without rewriting a whole new method just for that.

PS: In the example above, User_ is a JPA Static Metamodel

Answer 1

I think I just found an idea to implement this in the repository.

I just need to pass a list of attributes as a second argument.

get(Long userId, List<String> relations);

Or even better

get(Long userId, List<Attribute> relations);

The implementation of this will loop through the relations argument, and fetch them one by one.

The difficult part is when I have to deal with nested relations.