@OneToMany List<> vs Set<> difference

JavaJpa

Java Problem Overview

Is there any difference if I use

@OneToMany
public Set<Rating> ratings;

or if I use

@OneToMany
public List<Rating> ratings;

both work OK, i know difference between list and a set, however I don't know if this makes any difference how hibernate (or rather JPA 2.0) handles it.

Java Solutions

Solution 1 - Java

A list, if there is no index column specified, will just be handled as a bag by Hibernate (no specific ordering).

One notable difference in the handling of Hibernate is that you can't fetch two different lists in a single query. For example, if you have a Person entity having a list of contacts and a list of addresses, you won't be able to use a single query to load persons with all their contacts and all their addresses. The solution in this case is to make two queries (which avoids the cartesian product), or to use a Set instead of a List for at least one of the collections.

It's often hard to use Sets with Hibernate when you have to define equals and hashCode on the entities and don't have an immutable functional key in the entity.

Solution 2 - Java

If you use a List, then you can specify an 'Order BY' clause in getter function. You can't do that with a Set. The order by clause can contain partial EJBQL; For example

@OneToMany
@OrderBy("lastname ASC")
public List<Rating> ratings;

If you leave this field blank, then the list is sorted in ascending order based on the value of the primary key.

Categories
Recommended Java Solutions
Recommended Jpa Solutions

Previous Solution:

How can I check if a date is the same day as datetime.today()?

Python

Next Solution:

Is there an ExecutorService that uses the current thread?

JavaConcurrency

Attributions

All content for this solution is sourced from the original question on Stackoverflow.

The content on this page is licensed under the Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license.

Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionM4ksView Question on Stackoverflow
Solution 1 - JavaJB NizetView Answer on Stackoverflow
Solution 2 - JavaBasanth RoyView Answer on Stackoverflow