ORM gotchas - Child Mapping Issues

This is another work use-case example. We had a need to use some of the parent/child inheritance that ORM provides using a discriminator column (adobe's docs on using a subclass with discriminator).

The reasoning, is that there were specific types of children that had specific data attributes (it all revolved around a rule engine where the results had a shared set of data points, but depending on the rule type, the actual result data would change dramatically) and so, to avoid having a bunch of null values in the parent table, we were going to create the child tables appropriately.

Here's where it started to get tricky. We needed to map a relationship from the child object to a different table because, well because that relationship existed. Unfortunately, ORM didn't like that...

Being aware of ORM sessions and gotchas

So recently at work I was trying to troubleshoot an odd issue I had never seen before. I was getting an odd error from a relatively simple HQL query:

Root cause :org.hibernate.HibernateException: coldfusion.runtime.Cast$NumberConversionException: The value '' cannot be converted to a number.

Informative, right?

The query being ran was a simple fetch query along the lines of:

hql = "FROM artists WHERE id = :id";
artist = ormExecuteQuery( hql, {id = 1}, true); 

Basically, there was nothing to indicate that there was a numeric value that was being populated with a null string.

So where did the error come from?