Force field writes on update
----------------------------
Key: OPENJPA-38
URL: http://issues.apache.org/jira/browse/OPENJPA-38
Project: OpenJPA
Issue Type: New Feature
Environment: All
Reporter: David Ezzio
JPA supports use cases where optimistic checking is not desired. The
application need only avoid using a version field in the entity class.
However, OpenJPA optimizes its writes on update to include only those fields
that have changed. In cases, where optimistic checking is not used, OpenJPA
does not currently provide a way to write out some or all of the non-dirty
fields when writing an unchecked object with at least one dirty field. As a
result, when a class of objects is not checked, the changes from multiple
transactions are merged in the database.
For example, consider the class FooBar which has no version field. It has three
fields, id, mango and pommegranate. Assume there is a FooBar record that starts
off as the tuple,
<id = 100, mango = 'LARGE', pommegranate = 'LARGE'>.
With the current behavior, it would be changed to the tuple,
<id = 100, mango = 'SMALL', pommegranate = 'SMALL'>
by the following transactional sequence:
Tx A: tx.begin();
Tx A: foobar = em.find(FooBar.class, 100);
Tx B: tx.begin();
Tx B: foobar = em.find(FooBar.class, 100);
Tx A: foobar.mango = "SMALL";
Tx B: foobar.pommegrante = "SMALL";
Tx A: tx.commit();
Tx B: tx.commit();
Depending on the application's needs, this behavior might be acceptable, but it
might not be. The desired behavior may be that the result should be one of the
two following tuples.
Either,
<id = 100, mango = 'LARGE', pommegranate = 'SMALL'>
which is expected when Tx B commits last as shown above.
Or,
<id = 100, mango = 'SMALL', pommegranate = 'LARGE'>
if it happens that Tx A commits last.
To effect this behavior, a new feature could be added to OpenJPA. The use of
this feature would be triggered by a new, non-JPA annotation, perhaps called
EasilyDirtied, which when applied to a persistent attribute, would instruct
OpenJPA to write this attribute's value out on all updates to the object's
state. This annotation would be subservient to the mappedBy attribute in
relationship annotations. In other words, it has no effect if the annotaton is
applied to the mappedBy side of a relationship.
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