JPA entity modified by reflection not merged by entity manager

Question

I need to check if my actual entity is different from the old one.

I use reflection because my method must be standardized.

For each column, I update the value if and only if it's not null (because i read it from a CSV and a column may be not specified).

for(Field column : fields){
   column.setAccessible(true);
   Object newValue = column.get(myObject);
   if( newValue != null && !newValue.equals(column.get(oldObject))){
      column.set(oldObject, newValue);
   }
}

this.entitymanager.merge(oldObject)

If I do the changes like that, no UPDATE query is done.

If I change the value in the normal way oldobject.setValue(newValue) the query is done and the record is updated.

Why no UPDATE query is done by the entity manager if I change value via reflection?

I think it's because managed entities are proxy-ed and the setter invocation would do what you need. I'm not sure if this is possible the way you want it. — Peter, Jun 06 '19 at 09:04

score 2 · Answer 1 · answered Jun 06 '19 at 09:22

Just find some good information about such behaviour at this :

By default when using weaving/agent EclipseLink uses attribute change tracking to detect changes. This will not detect changes made through reflective field access (method access is ok though).

You can change the default using the @ChangeTracking annotation to deferred which will detect change made through reflection. i.e. @ChangeTracking(ChangeTrackingType.DEFERRED)

You could also disable weaving, or weaving of change tracking in the persistence.xml using, "eclipselink.weaving.changetracking"="false"

So there are couple of solutions that can try :

Use reflective method access
Change the ChangeTracking to deferred or even disable it
Disable weaving

Thank you. I'm testing the first solution – Daniele Licitra Jun 06 '19 at 10:12 — Daniele Licitra, Jun 06 '19 at 10:12

score 0 · Answer 2 · answered Jun 06 '19 at 10:34

Thank to @Ken Chan answer, I correct the method using getters and setters.

for(Field column : columns){
   Method mSet = myclass.getMethod("set"+ StringUtils.capitalize(column.getName()), column.getType());
   Method mGet = myclass.getMethod("get"+ StringUtils.capitalize(column.getName()));
   Object newValue = mGet.invoke(articolo);
   if( newValue != null && !newValue.equals(mGet.invoke(old))){
        mSet.invoke(old, newValue);
   }
 }

I must pay attention to methods' name. If entity have the property description, there must be also getDescription() and setDescription().

Now it works

JPA entity modified by reflection not merged by entity manager

2 Answers2