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Hibernate的3種繼承形式

1．     表和子類之間的對(duì)立一對(duì)一關(guān)系 Table per concrete class

源碼下載 http://download.csdn.net/source/226662
2．     每個(gè)子類對(duì)應(yīng)一張子表,并與主類共享主表 Table per subclass

源碼下載 http://download.csdn.net/source/226728
3．     表與類的一對(duì)多關(guān)系 Table per class hierarchy
源碼下載 http://download.csdn.net/source/226783

按照《深入潛出Hibernate》中介紹的，我們開始學(xué)習(xí)。

 

場(chǎng)景: 就一般的商品而言，在具備某些共性(如: 名稱,廠商),也有不同的屬性,如書有頁(yè)數(shù)，dvd有dvd的編碼格式.

 

<一> table per concerte class

(a) 使用xml

Titem 有兩個(gè)子類: Tbook , TDvd, 那么，所謂“表與子類之間的一對(duì)一的關(guān)系”，也就是每個(gè)子類對(duì)應(yīng)一張數(shù)據(jù)庫(kù)表。對(duì)應(yīng)Tbook , TDvd

數(shù)據(jù)庫(kù)的表我們?cè)O(shè)計(jì)如下

表 T_bool
id	Int	PK
Name	Varchar(50)
Manufacturer	Varchar(50)
Pagecount	int

 

表 T_dvd
id	Int	PK
Name	Varchar(50)
Manufacturer	Varchar(50)
Codetype	Varchar(30)

/**

* 虛擬的表

* TItem 已經(jīng)知道的繼承類為 AbstractTBook AbstractTDvd

*/

public abstract class TItem implements Serializable {

    private Integer id;

    private String name;

    private String manufacturer;

    public Integer getId() {

       return id;

       }

    public void setId(Integer id) {

       this.id = id;

       }

    public String getManufacturer() {

       return manufacturer;

       }

    public void setManufacturer(String manufacturer) {

       this.manufacturer = manufacturer;

       }

    public String getName() {

       return name;

       }

    public void setName(String name) {

       this.name = name;

       }

}

public abstract class AbstractTDvd extends TItem {

    private String codetype;

    public AbstractTDvd() {     }

    public String getCodetype() {

       return this.codetype;

       }

    public void setCodetype(String codetype) {

       this.codetype = codetype;

       }

}

public abstract class AbstractTBook extends TItem {

    private Integer pagecount;

    public AbstractTBook() {}

    public Integer getPagecount() {

       return this.pagecount;

       }

    public void setPagecount(Integer pagecount) {

       this.pagecount = pagecount;

       }

}

public class TDvd extends AbstractTDvd     {

    public TDvd() {}

}

public class TBook extends AbstractTDvd     {

    public TBook() {}

}

 

Tbook.hbm.xml

<?xml version="1.0" encoding="utf-8"?>

<hibernate-mapping>

       <class name="com.persist.tablePerConcreteClass.TBook" table="t_book" >

           <id name="id" type="java.lang.Integer">

               <column name="id" />

               <generator class="sequence">

               <param name="sequence">t_table_id_seq</param>

               </generator>

           </id>

           <property name="name" type="java.lang.String">

               <column name="name" length="50" />

           </property>

           <property name="manufacturer" type="java.lang.String">

               <column name="manufacturer" length="50" />

           </property>

           <property name="pagecount" type="java.lang.Integer">

               <column name="pagecount" />

           </property>

       </class>

</hibernate-mapping>

 

Tdvd.hbm.xml

<?xml version="1.0" encoding="utf-8"?>

<hibernate-mapping>

       <class name="com.persist.tablePerConcreteClass.TDvd" table="t_dvd" >

           <id name="id" type="java.lang.Integer">

               <column name="id" />

               <generator class="sequence">

               <param name="sequence">t_table_id_seq</param>

               </generator>

           </id>

           <property name="name" type="java.lang.String">

               <column name="name" length="50" />

           </property>

           <property name="manufacturer" type="java.lang.String">

               <column name="manufacturer" length="50" />

           </property>

           <property name="codetype" type="java.lang.String">

               <column name="codetype" length="50" />

           </property>

       </class>

</hibernate-mapping>

 

Hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>

<hibernate-configuration>

       <session-factory>

          <property name="dialect">

              org.hibernate.dialect.PostgreSQLDialect

          </property>

          <property name="connection.url">

              jdbc:postgresql://localhost:5432/postgres

          </property>

          <property name="connection.username">pgsql</property>

          <property name="connection.password">pgsql</property>

          <property name="connection.driver_class">

              org.postgresql.Driver

          </property>

          <property name="myeclipse.connection.profile">pgsql</property>

          <property name="show_sql">true</property>

          <mapping resource="com/persist/tablePerConcreteClass/TBook.hbm.xml" />

          <mapping resource="com/persist/tablePerConcreteClass/TDvd.hbm.xml" />

       </session-factory>

</hibernate-configuration>

測(cè)試用例

public class TBookDAO extends BaseHibernateDAO {

    public static void main(String args[]) {

       new TBookDAO().test();

       }

   

    public void test() {

          Session session = this.getSession();

          List list = session.createQuery(" from com.persist.tablePerConcreteClass.TItem").list();

          Iterator it = list.iterator();

       while (it.hasNext()) {

              TItem item = (TItem) it.next();

              System.out.println(item.getName());

          }

       }

}

 

(b) 使用hibernate注解
步驟1， 修改HibernateSessionFactory 中的Configuration為

AnnotationConfiguration configuration = new AnnotationConfiguration();

步驟2，修改hibernate.cfg.xml中的

<mapping resource="com/persist/tablePerConcreteClass/TBook.hbm.xml" />

<mapping resource="com/persist/tablePerConcreteClass/TDvd.hbm.xml" />

為

<mapping class="com.persist.tablePerConcreteClass.TBook"/>

<mapping class="com.persist.tablePerConcreteClass.TDvd"/>

步驟3，在Titem, AbstractTBook, AbstractTBook類上加注解

@MappedSuperclass

既Titem

@MappedSuperclass

public abstract class TItem implements Serializable {

    @Id

    @Column(name = "id")

    @SequenceGenerator(name = "t_table_id_seq", sequenceName = "t_table_id_seq")

    private Integer id;

    @Column(name = "name")

    private String name;

    @Column(name = "manufacturer")

    private String manufacturer;

    public Integer getId() {

       return id;

    }

    public void setId(Integer id) {

       this.id = id;

    }

    public String getManufacturer() {

       return manufacturer;

    }

    public void setManufacturer(String manufacturer) {

       this.manufacturer = manufacturer;

    }

    public String getName() {

       return name;

    }

    public void setName(String name) {

       this.name = name;

    }

}

AbstractTDvd

@MappedSuperclass

public class AbstractTDvd extends TItem {

    @Column(name = "codetype")

    private String codetype;

    public AbstractTDvd() { }

    public String getCodetype() {

       return this.codetype;

    }

    public void setCodetype(String codetype) {

       this.codetype = codetype;

    }

}

AbstractTBook

@MappedSuperclass

public class AbstractTBook extends TItem {

    @Column(name = "pagecount")

    private Integer pagecount;

    public AbstractTBook() {}

    public Integer getPagecount() {

       return this.pagecount;

    }   public void setPagecount(Integer pagecount) {

       this.pagecount = pagecount;

    }

}

步驟4，在Tbook,TDvd上加注解

@Entity

@Table(name = "t_book")

和

@Entity

@Table(name = "t_dvd")

調(diào)用的時(shí)候一樣
 

<二> Table per subclass

將父類Titem單獨(dú)映射到一張主表，而為Tbook, TDvd分別建立一張子表，子表和父表用外鍵來關(guān)聯(lián)

數(shù)據(jù)庫(kù)的表我們?cè)O(shè)計(jì)如下

表 T_item
id	Int	PK
Name	Varchar(50)
Manufacturer	Varchar(50)
CREATE TABLE t_item (  id int4 NOT NULL DEFAULT nextval('t_table_id_seq'::regclass),  name varchar(50),  manufacturer varchar(50),  CONSTRAINT t_item_pkey PRIMARY KEY (id) )

 

 

表 T_bool
id	Int	PK
Pagecount	int
CREATE TABLE t_book (  id int4 NOT NULL,  pagecount int4,  CONSTRAINT t_book_pkey PRIMARY KEY (id),  CONSTRAINT t_book_id_fkey FOREIGN KEY (id)       REFERENCES t_item (id) MATCH SIMPLE       ON UPDATE NO ACTION ON DELETE NO ACTION )

 

表 T_dvd
id	Int	PK
Codetype	Varchar(30)
CREATE TABLE t_dvd (  id int4 NOT NULL,  codetype varchar(30),  CONSTRAINT t_dvd_pkey PRIMARY KEY (id),  CONSTRAINT t_dvd_id_fkey FOREIGN KEY (id)       REFERENCES t_item (id) MATCH SIMPLE       ON UPDATE NO ACTION ON DELETE NO ACTION )

 

只有1個(gè)xml,TItem.hbm.xml
<hibernate-mapping>
     <class name="com.persist.tablePerConcreteClass.TItem" table="t_item">
         <id name="id" type="java.lang.Integer">
             <column name="id" />
             <generator class="sequence">
              <param name="sequence">t_table_id_seq</param>
             </generator>
         </id>
         <property name="name" type="java.lang.String">
             <column name="name" length="50" />
         </property>
         <property name="manufacturer" type="java.lang.String">
             <column name="manufacturer" length="50" />
         </property>
        
         <joined-subclass name="com.persist.tablePerConcreteClass.TBook" table="t_book">
          <key column="id"></key>
          <property name="pagecount" column="pagecount">
          </property>
         </joined-subclass>
         <joined-subclass name="com.persist.tablePerConcreteClass.TDvd" table="t_dvd">
          <key column="id"></key>
          <property name="codetype" column="codetype">
          </property>
         </joined-subclass>
     </class>
</hibernate-mapping>
使用注解
1.TItem不為抽象類,TItem的類注解為
@Entity
@Table(name = "t_item")
@Inheritance(strategy=InheritanceType.JOINED)
2.AbstractTBook和AbstractTDvd的類注解為
@PrimaryKeyJoinColumn(name="id")
3.TBook和TDvd的注解為
@Entity
@Table(name = "t_book")
和
@Entity
@Table(name = "t_dvd")

<三> Table per class hierarchy

CREATE TABLE t_item

(

 id int4 NOT NULL DEFAULT nextval('t_table_id_seq'::regclass),

 name varchar(50),

 manufacturer varchar(50),

 category varchar(30),

 codetype varchar(30),

 pagecount int4,

 CONSTRAINT t_item_pkey PRIMARY KEY (id)

)

只有一個(gè)xml,TItem.hbm.xml
<hibernate-mapping>
    <class name="com.persist.tablePerConcreteClass.TItem" table="t_item">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="sequence">
             <param name="sequence">t_table_id_seq</param>
            </generator>
        </id>
        <discriminator>
            <column name="category" length="10" />
        </discriminator>
        <property name="name" type="java.lang.String">
            <column name="name" length="50" />
        </property>
        <property name="manufacturer" type="java.lang.String">
            <column name="manufacturer" length="50" />
        </property>        
        <subclass name="com.persist.tablePerConcreteClass.TBook" discriminator-value="1">
         <property name="pagecount" column="pagecount">
         </property>
        </subclass>
        <subclass name="com.persist.tablePerConcreteClass.TDvd" discriminator-value="2" >
         <property name="codetype" column="codetype">
         </property>
        </subclass>
    </class>
</hibernate-mapping>
注解的修改為
1.TItem的注解修改為
@Entity
@Table(name = "t_item")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="category", discriminatorType=DiscriminatorType.STRING, length=30)
2.AbstractTBook, AbstractTDvd的注解修改為
@Inheritance
3.TBook,TDvd的注解修改為
@Entity
@DiscriminatorValue(value="2")

</script>