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I have the following question about JPA:
Can I save the order of the elements in a java.util.List? In my application the order in which I put elements in the Lists is important but after I get those collections from the database the order is not the same (as expected). Can you show me a way to deal with this problem?
P.S. There is not a field in the entities that I put in the collections by which I can order them.
Rosen
303
You can do that by JPA too but you will have to create a comma separated list of ids in the order you want. In your case you can keep same order. There is also one alternative using JPQL: You can use ,,FIELD'' instead of ,,FIND_IN_SET ''.
@OrderColumn annotation specifies a column that should maintain the persistent order of a list. The persistence provider maintains the order and also updates the ordering on insertion, deletion, or reordering of the list. This annotation can be used on @OneToMany or @ManyToMany relationship or on @ElementCollection .
The OrderColumn annotation is specified on a OneToMany or ManyToMany relationship or on an element collection. The OrderColumn annotation is specified on the side of the relationship that references the collection that is to be ordered.
save(…)- Method. It will persist or merge the given entity using the underlying JPA EntityManager. If the entity has not been persisted yet Spring Data JPA will save the entity via a call to the entityManager.
There are some hacky ways of doing this in JPA 1, but it's easiest to switch to a JPA 2 provider. The @OrderColumn annotation support is what you're looking for. Eclipselink have an ok tutorial on how to use it.
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