JPA dynamically EntityGraph and Subgraphs

Question

I created an util method:

public <T> Optional<T> fetch(Class<T> clazz, Object id, String... relations) {
    EntityGraph<T> graph = entityManager.createEntityGraph(clazz);
    Stream.of(relations).forEach(graph::addSubgraph);
    return Optional.ofNullable(entityManager.find(clazz, id, Collections.singletonMap("javax.persistence.loadgraph", graph)));
}

So if for example if User has lazy orders and wallets, I can do this:

Optional<User> user = fetch(User.class, 1, "orders", "wallets");

But I don't know how to take orders's or wallets lazy collections. It would be greate if I would call method like this:

Optional<User> user = fetch(User.class, 1, "orders", "orders.products", "wallet");

How can I extend the method to achieve this?

Boaris · Accepted Answer · 2016-11-25 05:51:50Z

I decided to use the next method:

public <T> Optional<T> fetch(Class<T> clazz, Object id, String... relations) {
    EntityGraph<T> graph = entityManager.createEntityGraph(clazz);
    Stream.of(relations).forEach(path -> {
        String[] splitted = path.split("\\.");
        Subgraph<T> root = graph.addSubgraph(splitted[0]);
        for (int i = 1; i < splitted.length; i++)
            root = root.addSubgraph(splitted[i]);
    });
    return Optional.ofNullable(entityManager.find(clazz, id, Collections.singletonMap("javax.persistence.loadgraph", graph)));
}

It has only one defect. The next two will work:

Optional<User> user = fetch(User.class, 1, "orders", "orders.products", "wallet");

Optional<User> user = fetch(User.class, 1, "orders.products", "wallet");

The next one will not:

Optional<User> user = fetch(User.class, 1, "orders.products", "orders", "wallet");

That's because orders overrides orders.products. I think it's enough, because logically if you want to load orders.products, you have to load orders anyway.

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