Hello,

I have a problem with accessing a field of a join table. Underneath you'll find the table-structure:

-------
table PERSON(ID, NAME)
table PERSON_PROJECT(PERSON_ID, PROJECT_ID, extra_column)
table PROJECT (ID, NAME)

The tables PERSON and PROJECT have a many-to-many relationship with each other.
-------

In the PERSON mapping file and in the PROJECT mapping file i created a Set, so that my domain object Person has a Set of projects and the Project domain object has a Set of persons.

The mappings look like this:
----------------
<class name="test.Project">
<property name="name" column="name"/>
...etc
<set name="persons" table="PERSON_PROJECT">
<key column="PROJECT_ID"/>
<many-to-many name="person" column="PERSON_ID" class="test.Person"/>
</set>
</class>

<class name="test.Person">
<property name="name" column="name"/>
...etc
<set name="projects" table="PERSON_PROJECT">
<key column="PERSON_ID"/>
<many-to-many name="project" column="PROJECT_ID" class="test.Project"/>
</set>
</class>
-------------------


This works fine...but.., i cannot get the "extra_column" field from my join table. This is because the join table is not configured as a class with it's own mapping file.

Is there a decent way to get a property from a join table? Does it mean that I have to create another class?? Do i have to work with the "<composite element>" tag? (Problem here is that the hibernate reference has an example, but does not show the tables and the domain objects....)

Could anyone please help me by providing a good example to solve my problem?

Regards,
Martijn

You do have to map the join table, at least as a composite-element, or you can map it as a class in its own right. There are many different ways to implement it, all reasonably obvious.

The exception would be when you have only one extra column, and it's a list index type: that is, it's some simple sequence based on one side of the relationship. Something like this:

• objA1, objB1, 1
• objA1, objB2, 2
• objA2, objB3, 1
• objA2, objB1, 2

In this case, you can implement it as a <list><many-to-many>, avoiding the need to map the join table.