如何使用EclipseLink更新MySQL表中的列？

Question

I am wondering how I can update a column in a table with EclipseLink. I tried using EntityManager.merge(myObject); but then EclipseLink throwed some exceptions saying it coudln´t update the other columns with a null value. I tried to add the @ChangeTracking property to my class I want to update so it just updates the column that has been changed, but it didn´t work and I even don´t know if that is the correct way to do it.

So how can I update just a single column in a table using EclipseLink?

Answer 1

If your merge isn't working, it is likely because you are creating a new instance from scratch and only attempting to populate the value you want to change. This results in merge overwriting all the other fields with null. Do not use em.merge on incomplete entities since it merges every JPA managed field - it has no way of knowing what you intended and must merge the entire state of the entity.

Instead use your changes to modify the managed instance. A simple example:

em.getTransaction().begin();
YourEntity instance = em.find(YourEntity.class, id);
instance.setYourAttribute(newValue);
em.getTransaction().commit();

Or a detached instance read in from an EM that you later use em.merge on.