Unidirectional associations with join tables
<class name="Person">
<id name="id" column="personId"> <generator class="native"/>
</id>
<set name="addresses"> <key column="personId"
not-null="true"/>
<one-to-many class="Address"/> </set>
</class>
<class name="Address">
<id name="id" column="addressId"> <generator class="native"/>
</id> </class>
create table Person ( personId bigint not null primary key )
create table Address ( addressId bigint not null primary key, personId bigint not null )
You should instead use a join table for this kind of association.
8.3. Unidirectional associations with join tables
8.3.1. One-to-many
A unidirectional one-to-many association on a join table is the preferred option. Specifying unique="true", changes the multiplicity from many-to-many to one-to-many.
<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> </class>
187
Chapter 8. Association Mappings
create table |
Person ( personId bigint |
not |
null primary key ) |
|
|
create |
table |
PersonAddress ( personId |
not |
null, addressId bigint not null primary key ) |
|
create |
table |
Address ( addressId bigint not null primary key |
) |
||
|
|
|
|
|
|
8.3.2. Many-to-one
A unidirectional many-to-one association on a join table is common when the association is
optional. For example:
<class name="Person">
<id name="id" column="personId">
<generator class="native"/>
</id>
<join table="PersonAddress"
optional="true">
<key column="personId" unique="true"/> <many-to-one name="address"
column="addressId"
not-null="true"/>
</join> </class>
<class name="Address">
<id name="id" column="addressId"> <generator class="native"/>
</id> </class>
create table |
Person ( personId bigint |
not null primary key ) |
|
||
create |
table |
PersonAddress ( personId |
bigint not |
null primary key, addressId bigint not null ) |
|
create |
table |
Address ( addressId bigint not null |
primary key |
) |
|
|
|
|
|
|
|
8.3.3. One-to-one
A unidirectional one-to-one association on a join table is possible, but extremely unusual.
<class name="Person">
<id name="id" column="personId">
<generator class="native"/>
</id>
<join table="PersonAddress"
optional="true">
<key column="personId"
unique="true"/>
<many-to-one name="address"
188
Many-to-many
column="addressId" not-null="true" unique="true"/>
</join> </class>
<class name="Address">
<id name="id" column="addressId"> <generator class="native"/>
</id> </class>
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
8.3.4. Many-to-many
Finally, here is an example of a unidirectional many-to-many association.
<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" class="Address"/>
</set> </class>
<class name="Address">
<id name="id" column="addressId"> <generator class="native"/>
</id> </class>
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null, addressId bigint not null, primary key (personId, addressId) )
create table Address ( addressId bigint not null primary key )
189