The question in my thread is: can only the owning side of a relation invoke
propgation of PERSIST, MERGE, REFRESH?
I have a self-referencing class "Competency". Each competency can have
child competencies and it can be itself a child competency of some other
parent competency.
A "composes" field holds a competency list of all child competencies.
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE,
CascadeType.REFRESH})
@JoinTable(name = "competency_composition")
public List<Competency> getComposes() {
return composes;
}
The inverse is stored in the field "composedBy" which is also a list of type
competency.
This also means that I use a bidirectional relationship.
@ManyToMany(
mappedBy = "composes",
cascade = {CascadeType.PERSIST, CascadeType.MERGE,
CascadeType.REFRESH})
public List<Competency> getComposedBy() {
return composedBy;
}
As you can see for cascading I use all types except for REMOVE. The reason
is, I just want to detach
a competency from its relations to other competencies without removing them.
To remove a competency I though I could just do the following:
a) set "composes" and "composedBy" to null
b) save the competency to propagate the deletion of relations in the
database
c) remove the competency from the database (wiithout touching other
competencies) by its DAO
It turns out that testing this in a DAO won't produce any error nor any
ConstraintViolationException
if the removed competency has actually parent competencies. While step b)
removes the competency from the database, the setting of "composedBy" to
null (or even to composedBy.clear()) is not propagated
to the parent competencies' "composes" field. Well, actually it is to some
extent: The reference to the deleted competency is set to Null, but this
Null object is not removed from the "composes" list.
Instead, to remove a competency properly, I have to
a) set "composes" to null
b) iterate through the "composedBy" list and remove the competency from all
its
parent competency's "composes" list.
c) save the parent competency by the DAO
c) remove the actual competency by the DAO.
So, is this the expected and correct behaviour?
Would be glad, if someone has an answer to this. Or some pointer to further
reading resources.
Thanks,
Martin
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