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Hibernate version: 3.0

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Is it possible to have a many-to-one relationship between a mapped class an component?

Referencing the following figure:

http://www.dafunks.com/hibernate/many-t ... oblems.jpg

I have:
0. component relationship from the Preferences class to the WarningPreferences class
1. one-to-many relationship from the WarningPreferences class to the WarnedUsers class
2. many-to-one relationship from the WarnedUsers class to the WarningPreferences class
3. many-to-one relationship from the WarnedUsers class to the Users class

But at runtime, I get an error about WarningPreferences being an unmapped class. Any suggestions as what to do in this scenario?

No, that's not possible if you plan on sharing instances (if you want pref.getWarningPreferences() to return the same as pref.getWarnedUsers().iterator().next().getWarningPreferences(), assuming that there's only one WarningPreference in your system). If you want the objects to be properly cached and resued, then you must map the class.

If you don't care (e.g. WarningPreferences is a read-only class) then you could map the component wherever it's needed. But that's not exactly good code resue :)

According to: http://www.hibernate.org/hib_docs/refer ... nents.html

The properties of a component may be of any Hibernate type (collections, many-to-one associations, other components, etc). Nested components should not be considered an exotic usage. Hibernate is intended to support a very fine-grained object model.

Is this not the case?

But mapping the class doesn't change the supported granularity.

The only problem with your mapping is that somewhere, you've told hibernate to load an instance of mapped class WarningPreferences, but you haven't actually mapped the class. A component is inherently unreferencable: it can be accessed only from the mapping that it's defined in. If you map it seperately, you can then reference it from anywhere.

It's like anonymous java classes: anything can call a method in an object of an anonymous class, but only one thing can create that object in the first place.