Relation many-to-many with attributes : how ?

Question

Hi, Excuse me for my poor english in advance as it is not my mother tongue.
Like in this example: http://www.xylax.net/hibernate/manytomany.html


But i have in the table foo-bar 2 attributes which are not part of the primary or foreign keys.: one boolean(A) & one string(B). I know how to map it without attributes but not in this case.

I have not found an answer in the documentation.

I need to know please how to map it & what kind of collection i have to declare in my class Foo.

Thanks in advance for your answer.

I really appreciate the time given by you.

Answer 1

I guess you will need to create a third class to hold these attributes

Answer 2

Quoting the I have a many-to-many association between two tables, but the association table has some extra columns (apart from the foreign keys). What kind of mapping should I use? entry of the Hibernate Users FAQ:

Use a composite-element to model the association table. For example, given the following association table:

create table relationship ( 
    fk_of_foo bigint not null, 
    fk_of_bar bigint not null, 
    multiplicity smallint, 
    created date )

you could use this collection mapping (inside the mapping for class Foo):

<set name="relationship">
    <key column="fk_of_foo"/>
    <composite-element class="Relationship">
        <property name="multiplicity" type="short" not-null="true"/>
        <property name="created" type="date" not-null="true"/>
        <many-to-one name="bar" class="Bar" not-null="true"/>
    </composite-element>
</set>

You may also use an <idbag> with a surrogate key column for the collection table. This would allow you to have nullable columns.

An alternative approach is to simply map the association table as a normal entity class with two bidirectional one-to-many associations.