ON UPDATE CASCADE not triggered in Hibernate JPA - postgresql

Question

See the following relations:
The Table RECIPE_USERCATEGORY_REL has an ON UPDATE CASCADE trigger, so if I would execute the following command in psql console, the value of ruc_ucat_category will also be updated automatically.
update usercategory set ucat_category = 'OldCategory' where ucat_category = 'NewCategory';
This works.
The problem is now Hibernate. I have this method in my service class:
public void renameCategory(String userId, String fromCategory, String toCategory)
{
TypedQuery<UserCategory> query = entityManager.createNamedQuery("UserCategory.findAllCaseSensitiveByUserIdAndPrefix", UserCategory.class);
query.setParameter(ApplicationConstants.PARAM_USER_ID, userId);
query.setParameter("category", fromCategory);
List<UserCategory> resultList = query.getResultList();
if (resultList == null || resultList.isEmpty())
{
return;
}
UserCategory userCategory = resultList.get(0);
userCategory.setCategory(toCategory);
}
I can assure that userCategory has the value 'OldCategory'. In my opinion, the update should work, because the trigger of the database should update the value of the relation table, but nothing happens. Why is this so?
Additional information: In my Entities, there is no #OneToMany and #ManyToOne declaration on the USERCATEGORY <-> RECIPE_USERCATEGORY_REL relationship (only on RECIPE <-> RECIPE_USERCATEGORY_REL relationship it is). This is because RECIPE_USERCATEGORY_REL is not a real join table. USERCATEGORY is similar to a growing lookup table, so Hibernate must not interfere the workflow here. The only relation of USERCATEGORY <-> RECIPE_USERCATEGORY_REL is the referential integrity in the database.
This is what the entity looks like, but as I said, there is no hibernate relation to the category table since Hibernate should not take care about this relation:
#Table(name = "RECIPE_USERCATEGORY_REL")
public class RecipeUserCategoryRel implements Serializable
{
private static final long serialVersionUID = 1L;
#EmbeddedId
private RecipeUserCategoryRelPk recipeUserCategoryRelPk = new RecipeUserCategoryRelPk();
#MapsId("rcpId")
#ManyToOne
#JoinColumn(name = "ruc_rcp_id", referencedColumnName = "rcp_id", insertable = false, updatable = false)
private Recipe recipe;
...
}
and...
#Embeddable
public class RecipeUserCategoryRelPk implements Serializable
{
private static final long serialVersionUID = 1L;
#Column(name = "ruc_rcp_id")
private Long rcpId;
#Column(name = "ruc_ucat_category")
private String category;
#Column(name = "ruc_ucat_acc_identifier")
private Long identifier;
public RecipeUserCategoryRelPk()
{
}
...
//getters, setters, hashcode, equals
}

Answer 1

I read in some other postings that it is not allowed in JPA to change the primary key. However, my use case is definitely changing the primary key, but in my case, it's not a common use case and no 'real' part of the application, but there are cases where users need to modify old data, so I need to provide this functionality.
(As workaround, I made a native update query)