Concurrent changes to attribute leave data in inconsistent state

[ledsoft]

When two concurrent transaction modify the same attribute of the same entity, both new values are saved in the repository.

Consider the following example, assuming Person.name is a singular attribute, T1 and T2 are transactions in separate persistence contexts (entity managers):

1. T1.begin()
2. T2.begin()
3. T1 load Person p as pT1
4. T2 load Person p as pT2
5. T1 set pT1.name = "T1 value"
6. T2 set pT2.name = "T2 value"
7. T1.commit()
8. T2.commit()

After this sequence, the repository contains both "T1 value" and "T2 value" for p, which causes IntegrityConstraintViolationExceptions on loading p because Person.name is a singular attribute.

[ledsoft]

Note that experiments with Eclipselink and Hibernate on the same scenario show that "T2 value" should be the only result - i.e., the last committed change overwrites any previous ones.