(1) Hibernate的3种继承形式 - HelloWorld 善战者,求之于势,不责于人;故能择人而任势。

Hibernate的3种继承形式

1．表和子类之间的对立一对一关系 Table per concrete class

源码下载 http://download.csdn.net/source/226662
2．每个子类对应一张子表,并与主类共享主表 Table per subclass

源码下载 http://download.csdn.net/source/226728
3．表与类的一对多关系 Table per class hierarchy
源码下载 http://download.csdn.net/source/226783

按照《深入潜出Hibernate》中介绍的，我们开始学习。

场景: 就一般的商品而言，在具备某些共性(如: 名称,厂商),也有不同的属性,如书有页数，dvd有dvd的编码格式.

<一> table per concerte class

(a) 使用xml

Titem 有两个子类: Tbook , TDvd, 那么，所谓“表与子类之间的一对一的关系”，也就是每个子类对应一张数据库表。对应Tbook , TDvd

数据库的表我们设计如下

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)

/**

* 虚拟的表

* TItem 已经知道的继承类为 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>

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

</generator>

</id>

</property>

</property>

</property>

</class>

</hibernate-mapping>

Tdvd.hbm.xml

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

<hibernate-mapping>

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

</generator>

</id>

</property>

</property>

</property>

</class>

</hibernate-mapping>

Hibernate.cfg.xml

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

<hibernate-configuration>

<session-factory>

org.hibernate.dialect.PostgreSQLDialect

</property>

jdbc:postgresql://localhost:5432/postgres

</property>

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

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

org.postgresql.Driver

</property>

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

</session-factory>

</hibernate-configuration>

测试用例

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
步骤1，修改HibernateSessionFactory 中的Configuration为

AnnotationConfiguration configuration = new AnnotationConfiguration();

步骤2，修改hibernate.cfg.xml中的

为

步骤3，在Titem, AbstractTBook, AbstractTBook类上加注解

@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;

}

步骤4，在Tbook,TDvd上加注解

@Entity

@Table(name = "t_book")

和

@Entity

@Table(name = "t_dvd")

调用的时候一样

<二> Table per subclass

将父类Titem单独映射到一张主表，而为Tbook, TDvd分别建立一张子表，子表和父表用外键来关联

数据库的表我们设计如下

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个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不为抽象类,TItem的类注解为
@Entity
@Table(name = "t_item")
@Inheritance(strategy=InheritanceType.JOINED)
2.AbstractTBook和AbstractTDvd的类注解为
@PrimaryKeyJoinColumn(name="id")
3.TBook和TDvd的注解为
@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)

)

只有一个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>
注解的修改为
1.TItem的注解修改为
@Entity
@Table(name = "t_item")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="category", discriminatorType=DiscriminatorType.STRING, length=30)
2.AbstractTBook, AbstractTDvd的注解修改为
@Inheritance
3.TBook,TDvd的注解修改为
@Entity
@DiscriminatorValue(value="2")

</script>

posted on 2007-08-12 16:47 helloworld2008 阅读(3016) 评论(1) 编辑收藏所属分类: java - hibernate

# re: (1) Hibernate的3种继承形式 2015-01-09 13:33 tangzhulong

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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 )