JAXB解组到托管JPA实体

Question

I've got a managed JPA entity (with subentities as well). Some of the fields of given entities should be filled by unmarshalling an XML file retrieved from another datasource. The problem is that JAXB will not unmarshall the XML into existing objects but create a new object instead. What is the simplest way to solve the problem?

Answer 1

Instead of unmarshalling into an existing JPA object, you should use the JPA merge operation to merge the state of the detached entity into a persistence context.

public void updateEmployee(Employee detachedEntity) {
   Employee managedEntity = entityManager.merge(detachedEntity);
   // do further operations on managedEntity and not detachedEntity
}

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UPDATE

If you are using JPA 2.1 then you could leverage entity graphs for this use case.