Hi ..

I was just exploring the powers of hibernate when i came across this scenario "I would like to implement a many to many relation in hibernate. Which is as under :-

1)Person Table
person id ( primary key)

2) Address Table
address id (primary key)

3) Person_Address (many to many mapping table)
person id (foreign key)
address id (foreign key)
count Integer (some dummy column )

classes mapping to these tables are
1) Person.java
2) Address.java
3)PersonAddress.java

Now, i would like to map it in such a way that i can retreive the count column of the person_address table. Most of the mappings tried by me only mapped person and address and i wasnt able to get the "count" information from person_address table. Can anyone help me to acheive this ?

Also find the sample mapping i used


Hibernate version: 3.1.13

Mapping documents:

<class name="Person">
<id name="id" column="personId">
<generator class="native"/>
</id>
<set name="addresses"
table="PersonAddress">
<key column="personId"/>
<many-to-many column="addressId"
unique="true"
class="Address"
/>
</set>
</class>
<class name="Address">
<id name="id" column="addressId">
<generator class="native"/>
</id>
<join table="PersonAddress"
inverse="true"
optional="true">
<key column="addressId"/>
<many-to-one name="person"
column="personId"
not-null="true"
/>
</join>
</class>

Any pointers on this would be highly appreciated.

Thanks in advance.

You have to map PersonAddress to do that. You can map it as a standalone entity, but I've always thought that a bit over the top. Define it as a named composite element.

If count is a list index (that is, each person gets its own sequence of count) then you can define the mapping as a simple many-to-many using the <list> collection, instead of <set>. This means that you don't have to map PersonAddress explicitly.

If count is unique for all rows in Person_Address, then you can define it to be part of a composite key of a fully mapped PersonAddress entity: that makes for a more complex mapping, but means that hibernate can look after generating the value in the column.

If neither of those options applies, go with the composite element mapping.