i've been weeding through the documentation and the forums for a few weeks now and it remains unclear to me how best to accomplish this.

take the classic, STUDENT, COURSE, STUDENT_COURSE scenario where
STUDENT_COURSE holds a GRADE column.

so we want to be able to accomplish the following tasks:

(1) given a STUDENT, obtain a collection of COURSEs that they have taken

(2) given a COURSE, obtain a collection of STUDENTs that have taken it

(3) given a STUDENT and a COURSE, obtain the associated GRADE

(4) perform queries such as:

(4.1) get me a list of STUDENTs that have gotten a 'B' in the 'math' COURSE

(4.2) get me a list of COURSEs that have been taken by STUDENTS named 'Fred'

From what i can gather, there are (at least) three approaches, and here are some pros and cons that i can see, please correct me if i'm wrong w.r.t. if they are appropriate approaches or pros/cons:

(A) two one-to-many's

pro:
- easiest to map and understand

con:
- many-to-many isn't explicit such that traversal is more tedious

notes:
- not too concerned with "tedium" as long as items (1-4) above can be accomplished with same performance as (B) and (C) below

- can someone provide syntax examples (or links to) for (1-4) above?

(B) composite-element

pro:
- as opposed to (A), would provide explicit support for traversal of many-to-many

con:
- would have to create redundant STUDENT_COURSE definitions on both STUDENT and COURSE mapping

(C) index-many-to-many

pro:
- as opposed to (A), would provide explicit support for traversal of many-to-many

- as opposed to (B), would allow for single definition of STUDENT_COURSE entity

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it seems that any non-trivial application would come across the need for an "associative entity" holding data, perhaps bi-directional traversal isn't strictly required, but i think all would benefit from an example similar to above with hbm files and code samples added perhaps to section 18 of the documentation.

I am trying to solve exacty the same problem and have also not found much about the details of how to do this. I think that a good example (including Java code) of this situation would be very valuable for many developers. If anyone can point to an example of breaking a many-to-many into two one-to-manys w/ an association entity, it would be greatly appreciated.

I had the similar issue but i never to use to one-to-many in place of many-to-many because one and only reason, the many-to-many relationship table had few more coulumns besides the compiste elements.

I had to create a separate class, in your example it would be StudentCourse.

StudentCourse {

Student s ;
Course c;
String grade;

// and other attributes.
}

tell me if this help
http://forum.hibernate.org/viewtopic.php?t=933543

be carefull of which collection you use on each side (see reference guide or hibernate in action)

Yes, this link was very helpful. I still don't have it working quite right, but I think it's because of the way I'm handling the collections within my Java code and also getting equals() and hashCode() correct.

Thanks.