Thursday, February 26, 2009

Hibernate: QueryException: could not instantiate: (updated)

I was doing some queries today in EJB-QL on JBossAS (which uses Hibernate as persistence provider).
And for a query that was nicely working in the Jopr Gui, I got errors in the test suite:


javax.ejb.EJBTransactionRolledbackException: java.lang.IllegalArgumentException: org.hibernate.QueryException: could not instantiate: com.acme.Foo
at ...... ( a lot ) ....
Caused by: java.lang.IllegalArgumentException: org.hibernate.QueryException: could not instantiate: com.acme.Foo


Ok nice - Hibernate can not instantiate my class because it can not instantiate my class. So what?

After looking some time at this and debugging around I found out that the issue was the following. But before I show you the code, let me assure that IntelliJ flagged it as valid and it did work in the UI.

But now the code:


SELECT new com.acme.FOO(res.name, res.id, ... , parent.name, parent.id)

FROM Resource res

LEFT OUTER JOIN res.parentResource parent

...

WHERE ...


The constructor of com.acme.Foo looked like this:


Foo(String res.name, int res.id, ... , String parentName, int parentId) {}


This is all valid,

but:

It can happen for Resources at the root of the hierarchy to not have a parent (when they are roots). And in this case, parent is null and Hibernate is looking for a constructor to pass NULL in as last argument, which does not fit for 'int'. Thus the failure to instantiate the class.

The correct constrctor looks like this:

Foo(String res.name, int res.id, ... , String parentName, Integer parentId) {}

(of course you need to update the respective property within Foo too).

Conclusion:
Just to get it straight: Hibernate is doing the right thing - it's only not easy to find out what is going wrong.




7 comments:

inbrain said...

Sincerely thank you, you saved lots of my time

Ignacio said...

Thanks! quick and clear answer to my problem.

Erika said...

In my case, it happened because one of the values that i was setting on the object was receiving a null from the data base. So, the constructor failed with a null pointer exception and then show me this error.

Thanks for your blog, it was very helpful.

Heiko W. Rupp said...

Erika, thanks for sharing.

Fouad said...

Thank you ! I have similar issue but the parameter was long, I was replaced it by Long, it works fine.

C├ędric Nicoloso said...

A big thank you for sharing that!

Rick said...

THANK YOU, THANK YOU!!!!

You just saved my back! I had to deliver this project for tomorrow and this was the exact problem I was dealing with!

Changing the parameter to Integer and using COALESCE solved my problem.

Thank yoU!!!