Red Hat Summit7.3. Unidirectional Associations with Join Tables
7.3.1. Unidirectional One-to-many with Join Tables
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>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 )
7.3.2. Unidirectional Many-to-one with Join Tables
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 )
7.3.3. Unidirectional One-to-one with Join Tables
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"
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 )
7.3.4. Unidirectional Many-to-many with Join Tables
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 )
