Hibernate的对象关系映射（6）

2.4 集合映射

java的collection和数组都可以被映射，意义在于表示数据之间的关联，对于hibernate管理的数据而言，java的集合对象主要起到了接口的作用。

2.4.1 Map

(1) index和element

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping  package ="com.weportal.collection" >
     < class  name ="Team" >
         < id  name ="id" >
             < generator  class ="hilo" />
         </ id >
         < property  name ="name"  column ="NAME"   />
         < map  name ="members"   order-by ="name,teamRole"   >
             < key  foreign-key ="fk" >
                 < column  name ="teamNumber" />
             </ key >
             < index  column ="teamRole"  type ="string" />
             < element  column ="name"  type ="string" />
         </ map >     
     </ class >
</ hibernate-mapping >

 (2) one-to-many

例如：如果将属性members（集合类型）映射到持久化类，需要使用one-to-many或者many-to-many。映射文件如下：

<? xml version = " 1.0 " ?>
<! DOCTYPE hibernate - mapping PUBLIC 
     " -//Hibernate/Hibernate Mapping DTD 3.0//EN "
     " http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd " >
< hibernate - mapping package = " com.weportal.collection " >
     < class  name = " Team " >
         < id name = " id " >
             < generator  class = " hilo " />
         </ id >
         < property name = " name "  column = " NAME "   />
         < map name = " members "   inverse = " false "   >
             < key column = " team "  foreign - key = " fk " >
             </ key >
             < index column = " teamRole "  type = " string " />
             < one - to - many  class = " Member " />
         </ map >     
     </ class >
     < class  name = " Member " >
         < id name = " id " >
             < generator  class = " native " ></ generator >
         </ id >
         < property name = " name " ></ property >
         < property name = " age " ></ property >
         < many - to - one name = " team " ></ many - to - one >
     </ class >
</ hibernate - mapping >

(3) many-to-many

建立这种多对多的关系不是一个优秀的方案。

(4) composite-index

Map中的index元素可以被替换为存储组件对象的composite-index，利用composite-index可将组件用于index。

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping  package ="com.weportal.collection" >
     < class  name ="Team" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name"  column ="NAME"   />
         < map  name ="members"  inverse ="false" >
             < key  column ="team"  foreign-key ="fk" />
             < composite-index  class ="Position" >
                 < key-property  name ="role" />
                 < key-property  name ="scene" />
                 < key-many-to-one  name ="bestChoice"  class ="Member" />
             </ composite-index >
             < one-to-many  class ="Member" />
         </ map >
     </ class >
     < class  name ="Member" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name" />
         < property  name ="age" />
         < many-to-one  name ="team" />
     </ class >
</ hibernate-mapping >

(5) index-many-to-many

index不仅可以是组件，也可以是持久化类的实体。

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping  package ="com.weportal.collection" >
     < class  name ="Team" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name"  column ="NAME"   />
         < map  name ="members"  inverse ="false" >
             < key  column ="team"  foreign-key ="fk" />
             < index-many-to-many  class ="Position"  column ="id" ></ index-many-to-many >
             < one-to-many  class ="Member" />
         </ map >
     </ class >
     < class  name ="Member" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name" />
         < property  name ="age" />
         < many-to-one  name ="team" />
     </ class >
     < class  name ="Position" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="role" />
         < property  name ="scene" />
         < many-to-one  name ="bestChoice" />
     </ class >     
</ hibernate-mapping >

(6) index-many-to-any

index还可以插入any类型的数据，any在hibernate中代表不确定的类型。

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping  package ="com.weportal.collection" >
     < class  name ="Team" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name"  column ="NAME"   />
         < map  name ="members"  inverse ="false" >
             < key  column ="team"  foreign-key ="fk" />
             < index-many-to-any  id-type ="long"  meta-type ="string" >
              < column  name ="index_class" ></ column >
              < column  name ="index_id" ></ column >              
             </ index-many-to-any >
             < one-to-many  class ="Position" />
         </ map >
     </ class >
     < class  name ="Member" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name" />
         < property  name ="age" />
         < many-to-one  name ="team" />
     </ class >     
     < class  name ="Position" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="role" />
         < property  name ="scene" />
         < many-to-one  name ="bestChoice" />
     </ class >         
</ hibernate-mapping >

(7) many-to-any

value的值也可设为any类型。

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping  package ="com.weportal.collection" >
     < class  name ="Team" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name"  column ="NAME"   />
         < map  name ="members"  inverse ="false" >
             < key  column ="team"  foreign-key ="fk" />
             < index-many-to-any  id-type ="long"  meta-type ="string" >
              < column  name ="index_class" ></ column >
              < column  name ="index_id" ></ column >              
             </ index-many-to-any >
             < many-to-any  id-type ="long"  meta-type ="string" >
              < column  name ="value_class" ></ column >
              < column  name ="value_id" ></ column >
             </ many-to-any >
         </ map >
     </ class >
     < class  name ="Member" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name" />
         < property  name ="age" />
         < many-to-one  name ="team" />
     </ class >     
     < class  name ="Position" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="role" />
         < property  name ="scene" />
         < many-to-one  name ="bestChoice" />
     </ class >         
</ hibernate-mapping >

(8) composite-element

可以用来声明更复杂的数据元素。

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping  package ="com.weportal.collection" >
     < import  class ="Member" ></ import >
     < class  name ="Team" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name"  column ="NAME"   />
         < map  name ="members"  table ="teamMembers" >
             < key  column ="teamId" />
             < index  column ="teamRole"  type ="string" />
             < composite-element  class ="Member" >
                 < parent  name ="team" />
                 < property  name ="name" />
                 < property  name ="age" />                 
             </ composite-element >
         </ map >
     </ class >
</ hibernate-mapping >

可以利用nested-composite-element在类中嵌套类。

<? xml version="1.0" ?>
<! DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping  package ="com.weportal.collection" >
     < import  class ="Member" ></ import >
     < class  name ="Team" >
         < id  name ="id" >
             < generator  class ="native" />
         </ id >
         < property  name ="name"  column ="NAME"   />
         < map  name ="members"  table ="teamMembers" >
             < key  column ="teamId" />
             < index  column ="teamRole"  type ="string" />
             < composite-element  class ="Member" >
                 < parent  name ="team" />
                 < property  name ="name" />
                 < property  name ="age" />
                 < nested-composite-element  name ="assistantMember"  class ="Member" >
                     < property  name ="name"  column ="assistant" ></ property >
                 </ nested-composite-element >             
             </ composite-element >
         </ map >
     </ class >
</ hibernate-mapping >

(9) Map的排序

利用sort和order-by属性来声明。

(10) Map的子元素和属性

略