Hibernate version: 3.1.3
Name and version of the database you are using: MySQL 5

I've been looking through the reference docs (especially the section on advanced collection mapping), but don't see anything that talks about this particular situation:

I need to map a many-to-many relationship between instances of the same entity type. The twist is that I need to have a "note" attached to each such association.
In non-abstract terms: my entities are Books, and any Book can be associated with any number of other Books. When such an association exists, I need to persist a note about that particular relationship.

If it were just a matter of the database schema, I would just add a column to the relation table. Can this be done with just a <set> and <many-to-many> mapping? I don't think so, because what would Hibernate do with the data in the "note" column?
So my thinking is that I'll have to model the relationship itself as an entity - is that the way to go? If so, what is the best way to query for all such entity instances given a particular Book, and can it be made part of the lazy fetch of the Book in question or must it be a separate query?
Finally, an example using the Criteria API would probably help me a great deal, if you've got the inclination to go that far.

Thanks in advance,
Eric

a question, how do you do the same thing in Java?

how do you access the note property when you only have books and collection of books?

I believe you must map the join table (with additional fields) to anothere entity.

You have two options:

1) An intermediate Entity Class for the join table with one-to-many mappings


2) Using a collection of components which is described here:
http://www.hibernate.org/hib_docs/v3/re ... ollections
You should be aware that bidirectional navigation is NOT supported with this approach.
This mapping is copy pasted from the Hibernate documentation, I have just marked the interesting part of this kind of mapping.

<class name="eg.Order" .... >
....
<set name="purchasedItems" table="purchase_items" lazy="true">
<key column="order_id">
<composite-element class="eg.Purchase">
<property name="purchaseDate"/>
<property name="price"/>
<property name="quantity"/>
<many-to-one name="item" class="eg.Item"/>
</composite-element>
</set>
</class>

Thanks - I was paying attention to Chapters 6 & 7, but missed this part of Chapter 8 somehow. It looks promising - thanks!