JPA - create-if-not-exists entity?

user_2827 0
Viewed 56713

I have several mapped objects in my JPA / Hibernate application. On the network I receive packets that represent updates to these objects, or may in fact represent new objects entirely.

I'd like to write a method like 

<T> T getOrCreate(Class<T> klass, Object primaryKey)

that returns an object of the provided class if one exists in the database with pk primaryKey, and otherwise creates a new object of that class, persists it and returns it.

The very next thing I'll do with the object will be to update all its fields, within a transaction.

Is there an idiomatic way to do this in JPA, or is there a better way to solve my problem?

jpa hibernate database java
5 Answers

I must point out there's some flaw in @gus an's answer. It could lead to an apparent problem in a concurrent situation. If there are 2 threads reading the count, they would both get 0 and then do the insertion. So duplicate rows created.

My suggestion here is to write your native query like the one below:

insert into af_label (content,previous_level_id,interval_begin,interval_end) 
    select "test",32,9,13
    from dual 
    where not exists (select * from af_label where previous_level_id=32 and interval_begin=9 and interval_end=13)

It's just like an optimistic lock in the program. But we make the db engine to decide and find the duplicates by your customized attributes.

user_85869410

How about use orElse function after findByKeyword? You can return a new instance if no record is found.

        SearchCount searchCount = searchCountRepository.findByKeyword(keyword)
                .orElse(SearchCount.builder()
                        .keyword(keyword)
                        .count(0)
                        .build()) ;
user_118993230

There is an easy solution to have this tackled even in a concurrent environment.

Use optimistic locking on your entities with @Version private Long version; and <column name="version" type="BIGINT"/> in your liquibase table creation. If you try to save a new entity thats (composite) p_pkey already exists, a DataIntegrityViolationException will be thrown up to the JpaRepository. So there's no need to worry about concurrent locking in your service layer - the database will know if an entity exists.

user_144915500
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