hibernate关联映射
单向关联
多对一(many to one)
单向many-to-one关联是最常见的单向关联关系。
<class name="Person">
<id name="id" column="personId">
<generator
column="addressId"
not-null="true"/>
</class>
<class name="Address">
<id name="id" column="addressId">
<generator column="personId">
<generator
column="addressId"
unique="true"
not-null="true"/>
</class>
<class name="Address">
<id name="id" column="addressId">
<generator column="personId">
<generator column="personId">
<generator constrained="true"/>
</class>
create table Person ( personId bigint not null primary key )
create table Address ( personId bigint not null primary key )
一对多（one to many）
基于外键关联的单向一对多关联是一种很少见的情况，并不推荐使用。
<class name="Person">
<id name="id" column="personId">
<generator
not-null="true"/>
<one-to-many column="addressId">
<generator column="personId">
<generator table="PersonAddress">
<key column="personId"/>
<many-to-many column="addressId"
unique="true"
column="addressId">
<generator column="personId">
<generator
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 column="personId">
<generator
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 column="personId">
<generator table="PersonAddress">
<key column="personId"/>
<many-to-many column="addressId"
column="addressId">
<generator column="personId">
<generator
column="addressId"
not-null="true"/>
</class>
<class name="Address">
<id name="id" column="addressId">
<generator inverse="true">
<key column="addressId"/>
<one-to-many and insert="false"来对另一端反向操作）。
<class name="Person">
<id name="id"/>
...
<many-to-one name="address"
column="addressId"
not-null="true"
insert="false"
update="false"/>
</class>
<class name="Address">
<id name="id"/>
...
<list name="people">
<key column="addressId" not-null="true"/>
<list-index column="peopleIdx"/>
<one-to-many column="personId">
<generator
column="addressId"
unique="true"
not-null="true"/>
</class>
<class name="Address">
<id name="id" column="addressId">
<generator
property-ref="address"/>
</class>
create table Person ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
基于主键关联的一对一关联需要使用特定的id生成器。
<class name="Person">
<id name="id" column="personId">
<generator column="personId">
<generator
constrained="true"/>
</class>
create table Person ( personId bigint not null primary key )
create table Address ( personId bigint not null primary key )
使用连接表的双向关联
一对多（one to many） /多对一（ many to one）
基于连接表的双向一对多关联。注意inverse="true"可以出现在关联的任意一端，即collection端或者join端。
<class name="Person">
<id name="id" column="personId">
<generator
table="PersonAddress">
<key column="personId"/>
<many-to-many column="addressId"
unique="true"
column="addressId">
<generator
inverse="true"
optional="true">
<key column="addressId"/>
<many-to-one name="person"
column="personId"
not-null="true"/>
</join>
</class>
create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null, addressId bigint not null primary key )
create table Address ( addressId bigint not null primary key )
一对一（one to one）
基于连接表的双向一对一关联极为罕见，但也是可行的。
<class name="Person">
<id name="id" column="personId">
<generator
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
optional="true"
inverse="true">
<key column="addressId"
unique="true"/>
<many-to-one name="person"
column="personId"
not-null="true"
unique="true"/>
</join>
</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 )
多对多（many to many）
最后，还有 双向多对多关联.
<class name="Person">
<id name="id" column="personId">
<generator column="addressId">
<generator inverse="true" table="PersonAddress">
<key column="addressId"/>
<many-to-many column="personId"
class="Person"/>
</set>
</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 )
