We have a parent-child relation with

	@OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, orphanRemoval = true)
	Set<Child> getChildren()

on the parent-side and

	@ManyToOne(optional = false)
	Parent getParent()

on the children-side. So basically the children cannot exist without a parent.

If we now create a parent with children, add the entities to the entity manager, remove one child and flush those changes, we end up with very different results depending on if we used persist or merge and flushing or not in the first place.

• persist works as expected (flushed or not)
• merge works only if the initial parent was flushed

If we however merge without flushing, it depends on whether we clear the parent on the child side:

• If the parent is not cleared, the orphan child is inserted and effectively not removed as orphanRemoval suggests
• If the parent is cleared, Hibernate tries to insert the orphan child into the database and fails with the null reference to the parent

Since both cases work perfectly with persist (instead of merge), we would expect the very same behavior after an initial merge? Is this expectation justified? Or are we doing something wrong?

This may be related with

You may find another very small stripped down test project for these cases on Github https://github.com/abenneke/sandbox/tree/master/hibernate-flush-remove

Thank you!