Hi everyone, I'm new to Hibernate and got this problem when trying to map the classes. I have 2 classes UnitDescription and UnitConversion.
UnitDescription has a Map<Integer, UnitConversion> (containing all the conversions it could have).
UnitConversion has 2 attributes 'from' and 'to', both are type UnitDescription (specifying source unit and target unit of conversion).
So the result is some relation 2-to-many, I can't use many-to-one at 'from' and 'to', because doing so will create duplicated columns in table UnitConversion (2 foreign keys with the same names).
Now I don't have any idea how to resolve it. Please give me an advice about this situation.

I'm not understanding your object model, because it appears (and I could be wrong) that you're also trying to capture database-like table associations as well.

Ignoring Hibernate for the moment, what do the raw classes look like, and what is the map in UnitDescrption for?

A concrete example like "this is how inches to feet are represented with my classes" would help.

This derived code from your text is confusing to me:

The standard aproach for this is to use a List with two elements.