org.hibernate.AssertionFailure: null identifier

I hate Hibernate with a passion!
More in general, I tend to hate ORM pretty much, because I feel like I need to adapt my applications and code to what the ORM thinks it should be. However, I have to use some ORMs, most notably Hibernate (I’m not reporting the version because it is awkwardly old).

Anyway, yesterday I start seeing this strange exception on one of applications of mine:
ERROR     AssertionFailure                         <init> - an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)
org.hibernate.AssertionFailure: null identifier
	at org.hibernate.engine.EntityKey.<init>(
	at org.hibernate.loader.Loader.extractKeysFromResultSet(
Searching the web did not provide me any hint about, and that is the reason why I’m writing this post.

Trying to identify the problem

My first try was to enable as much logging as I could: 
but that does not revelead nothing interesting, since the problem wa not in a query rather in the query result. I then turned off the above variables and let Hibernate to log at a DEBUG level. That was enlightning because it revealed me a line like the following:
DEBUG StatefulPersistenceContext   initializeNonLazyCollections - initializing non-lazy collections
Wait a minute: what does initialize non-lazy collections means?

I did a code scan on the entities just to find out I’ve got a collection @ManyToOne with a fecthing type of EAGER, and most notably the value I was trying to fecth was set to null.
So the workflow was as follows: 1) I did load entity A; 2) entity A has a @OneToOne relationship with entity B, so the latter is loaded by “reflection”; 3) entity B has a @ManyToOne relationship with entity C and tries to EAGER-ly fetch it. The point 3 is, of course, the problem.

The solution

Having identified the problem, hitting the solution was quite easy: change the @ManyToOne fetching type from EAGER to LAZY. Please note that even setting EAGER with optional = true did not work.

Again, I hate Hibernate with a passion!

The article org.hibernate.AssertionFailure: null identifier has been posted by Luca Ferrari on October 22, 2019