?二、單向關系
?1.“單向一對多關系”
?基于外鍵關聯的單向一對多關聯是一種很少見的情況，并不推薦使用
?<class name="com.jason.associations.one2many.unilateralism.one2many.Person" table="Person">
??<id name="id" column="personId">
??????<generator class="native"/>
??</id>
??<set name="addresses" cascade="all">
??????<!--key 是Address表的字段，最后要update Address表.personId = Person表.personId-->
??????<key column="personId"??not-null="true"/>
??????<one-to-many?
??????????class="com.jason.associations.one2many.unilateralism.one2many.Address"/>
??</set>
??<property name="name" column="personName" type="string" />
?</class>
?
?<class name="com.jason.associations.one2many.unilateralism.one2many.Address" table="Address">
?????<id name="id" column="addressId">
?????????<generator class="native"/>
??????</id>
?????<property name="country" column="country" type="string" />
?????<property name="city" column="city" type="string" />
?</class>
?<!--
?????create table Person ( personId bigint not null primary key, personName varchar(20))
?????create table Address ( addressId bigint not null primary key, personId bigint not null, country varchar(20), city varchar(20) )
?-->
?
?
?2.“單向多對一關系”
??<class name="com.jason.associations.one2many.unilateralism.many2one.Person" table="Person">
??<id name="id" column="personId">
??????<generator class="native"/>
??</id>
??<many-to-one name="address"?
???????class="com.jason.associations.one2many.unilateralism.many2one.Address"
???????column="addressId"?
???????cascade="all"
???????outer-join="auto"
???????update="true"
???????insert="true"
???????access="property"
???????not-null="true"/>
??<property name="name" column="personName" type="string" />
?</class>
?
?<class name="com.jason.associations.one2many.unilateralism.many2one.Address" table="Address">
??<id name="id" column="addressId">
??????<generator class="native"/>
??</id>
??<property name="country" column="country" type="string" />
??<property name="city" column="city" type="string" />
?</class>
?<!--
?????create table Person ( personId bigint not null primary key, addressId bigint not null, personName varchar(20))
?????create table Address ( addressId bigint not null primary key, country varchar(20), city varchar(20) )
?-->

3、“單向一對多連接表關系”
<hibernate-mapping>
?<class name="com.jason.associations.one2many.unilateralism.one2many.table.Person" table="Person">
??<id name="id" column="personId">
??????<generator class="native"/>
??</id>
??<set name="addresses" table="PersonAddress" cascade="all">
??????<key column="personId"/>
??????<many-to-many column="addressId"
??????????unique="true"
??????????class="com.jason.associations.one2many.unilateralism.one2many.table.Address"/>
??</set>
??<property name="name" column="personName" type="string" />
?</class>
?
?<class name="com.jason.associations.one2many.unilateralism.one2many.table.Address" table="Address">
??<id name="id" column="addressId">
??????<generator class="native"/>
??</id>
??<property name="country" column="country" type="string" />
??<property name="city" column="city" type="string" />
?</class>
?<!--
?????create table Person ( personId bigint not null primary key, personName varchar(20))
?????create table PersonAddress ( personId bigint not null, addressId bigint not null primary key)
?????create table Address ( addressId bigint not null primary key, country varchar(20), city varchar(20))
?-->

?4、“單向多對一連接表關系”
?我們認為對于這種關聯關系最好使用連接表。
??<class name="com.jason.associations.one2many.unilateralism.many2one.table.Person" table="Person">
??<id name="id" column="personId">
??????<generator class="native"/>
??</id>
??<property name="name" column="personName" type="string" />
??<!--join 必須放在最下面-->
??<join table="PersonAddress" optional="true">
?????????? <key column="personId" unique="true"/>
?????????? <many-to-one name="address"?
??????????????????class="com.jason.associations.one2many.unilateralism.many2one.table.Address"
??????????????????column="addressId"?
??????????????????not-null="true"?
??????????????????cascade="all"/>
????</join>?
?</class>
?
?<class name="com.jason.associations.one2many.unilateralism.many2one.table.Address" table="Address">
??<id name="id" column="addressId">
??????? ?<generator class="native"/>
??</id>
??<property name="country" column="country" type="string" />
??<property name="city" column="city" type="string" />
?</class>
?<!--
?????create table Person ( personId bigint not null primary key, personName varchar(20))
?????create table PersonAddress ( personId bigint not null primary key, addressId bigint not null)
?????create table Address ( addressId bigint not null primary key, country varchar(20), city varchar(20))
?-->
?
?
?二、雙向關系
?雙向一對多關系就是二者的組合
?為了更好地提高執行效率，需要將“多”的一端設為主控方，就是將關聯關系的維護工作交給“多”的一端。