JPA Advanced Mappings(映射)

知識 08-01

JPA Advanced Mappings(映射)

JPA是一個使用java規範發布的庫。因此，它支持所有面向對象的實體持久性概念。

繼承策略

繼承是面向對象語言的核心概念，因此我們可以在實體之間使用繼承關係或策略。JPA支持三種類型的繼承策略，如SINGLE_TABLE，JOINED_TABLE和TABLE_PER_CONCRETE_CLASS。

Staff, TeachingStaff, NonTeachingStaff關係：

JPA Advanced Mappings(映射)

單表策略

單表策略採用所有類欄位（超類和子類），並將其映射到稱為SINGLE_TABLE策略的單個表中。鑒別器值在區分一個表中三個實體的值時起關鍵作用。

讓我們考慮上面的例子，TeachingStaff和NonTeachingStaff是類員工的子類。提醒繼承的概念（是通過子類繼承超類的屬性的機制），因此sid，sname是屬於TeachingStaff和NonTeachingStaff的欄位。創建一個JPA項目。本項目的所有模塊如下：

創建實體

在「src」包下創建一個名為「com.tutorialspoint.eclipselink.entity」的包。在給定的包下創建一個名為Staff.java的新Java類。Staff實體類顯示如下：

package com.tutorialspoint.eclipselink.entity;


import java.io.Serializable;
import javax.persistence.DiscriminatorColumn;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.Inheritance;

import javax.persistence.InheritanceType;

import javax.persistence.Table;
@Entity

@Table

@Inheritance( strategy = InheritanceType.SINGLE_TABLE )

@DiscriminatorColumn( name = "type" )
public class Staff implements Serializable {

   @Id

   @GeneratedValue( strategy = GenerationType.AUTO )
   private int sid;

   private String sname;
   public Staff( int sid, String sname ) {

      super;

      this.sid = sid;

      this.sname = sname;

   }
   public Staff {

      super;

   }
   public int getSid {

      return sid;

   }
   public void setSid( int sid ) {

      this.sid = sid;

   }
   public String getSname {

      return sname;

   }

public void setSname( String sname ) { this.sname = sname; } }

在上述代碼中，@DescriminatorColumn指定欄位名稱（type），其值顯示剩餘的（Teaching and NonTeachingStaff）欄位。

在com.tutorialspoint.eclipselink.entity包下創建一個名為TeachingStaff.java的 Staff類的子類（class）。TeachingStaff實體類顯示如下：

package com.tutorialspoint.eclipselink.entity;


import javax.persistence.DiscriminatorValue;

import javax.persistence.Entity;
@Entity

@DiscriminatorValue( value="TS" )

public class TeachingStaff extends Staff {
   private String qualification;

   private String subjectexpertise;
   public TeachingStaff( int sid, String sname, 
   String qualification,String subjectexpertise ) {

      super( sid, sname );

      this.qualification = qualification;

      this.subjectexpertise = subjectexpertise;

   }
   public TeachingStaff {

      super;

   }
   public String getQualification{

      return qualification;

   }
   public void setQualification( String qualification ){

      this.qualification = qualification;

   }
   public String getSubjectexpertise {

      return subjectexpertise;

   }

public void setSubjectexpertise( String subjectexpertise ){ this.subjectexpertise = subjectexpertise; } }

在com.tutorialspoint.eclipselink.entity包下創建一個名為NonTeachingStaff.java的 Staff類的子類（class）。NonTeachingStaff實體類顯示如下：

package com.tutorialspoint.eclipselink.entity;


import javax.persistence.DiscriminatorValue;

import javax.persistence.Entity;
@Entity

@DiscriminatorValue( value = "NS" )
public class NonTeachingStaff extends Staff {

   private String areaexpertise;
   public NonTeachingStaff( int sid, String sname, String areaexpertise ) {

      super( sid, sname );

      this.areaexpertise = areaexpertise;

   }
   public NonTeachingStaff {

      super;

   }
   public String getAreaexpertise {

      return areaexpertise;

   }

public void setAreaexpertise( String areaexpertise ){ this.areaexpertise = areaexpertise; } }

persistence.xml中

Persistence.xml文件包含實體類的資料庫和註冊信息的配置信息。xml文件顯示如下：

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


<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"

   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

   xsi:schemaLocation="http://java.sun.com/xml/ns/persistence

   http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
   <persistence-unit name="Eclipselink_JPA" transaction-type="RESOURCE_LOCAL">
      <class>com.tutorialspoint.eclipselink.entity.Staff</class>

      <class>com.tutorialspoint.eclipselink.entity.NonTeachingStaff</class>

      <class>com.tutorialspoint.eclipselink.entity.TeachingStaff</class>
      <properties>

         <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/jpadb"/>

         <property name="javax.persistence.jdbc.user" value="root"/>

         <property name="javax.persistence.jdbc.password" value="root"/>

         <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>

         <property name="eclipselink.logging.level" value="FINE"/>

         <property name="eclipselink.ddl-generation" value="create-tables"/>

      </properties>

</persistence-unit> </persistence>

Service class

服務類是業務組件的實現部分。在名為"com.tutorialspoint.eclipselink.service"的"src"包下創建一個包。

在給定的包下創建一個名為SaveClient.java的類來存儲Staff，TeachingStaff和NonTeachingStaff類欄位。SaveClient類顯示如下：

package com.tutorialspoint.eclipselink.service;


import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.Persistence;

import com.tutorialspoint.eclipselink.entity.NonTeachingStaff;

import com.tutorialspoint.eclipselink.entity.TeachingStaff;
public class SaveClient {
   public static void main( String[ ] args ) {
      EntityManagerFactory emfactory = Persistence.createEntityManagerFactory( "Eclipselink_JPA" );

      EntityManager entitymanager = emfactory.createEntityManager;

      entitymanager.getTransaction.begin;
      //Teaching staff entity

      TeachingStaff ts1=new TeachingStaff(1,"Gopal","MSc MEd","Maths");

      TeachingStaff ts2=new TeachingStaff(2, "Manisha", "BSc BEd", "English");
      //Non-Teaching Staff entity

      NonTeachingStaff nts1=new NonTeachingStaff(3, "Satish", "Accounts");

      NonTeachingStaff nts2=new NonTeachingStaff(4, "Krishna", "Office Admin");
      //storing all entities

      entitymanager.persist(ts1);

      entitymanager.persist(ts2);

      entitymanager.persist(nts1);

      entitymanager.persist(nts2);
      entitymanager.getTransaction.commit;

entitymanager.close; emfactory.close; } }

編譯和執行上述程序後，您將在Eclipse IDE的控制面板中收到通知。檢查MySQL工作台的輸出。表格格式的輸出如下所示：

Sid	Type	Sname	Areaexpertise	Qualification	Subjectexpertise
1	TS	Gopal	-	MSC MED	Maths
2	TS	Manisha	-	BSC BED	English
3	NS	Satish	Accounts
4	NS	Krishna	Office Admin

最後，您將獲得包含所有三類欄位的單表，並與名為「Type」（欄位）的discriminator列不同。

加盟表策略

加入表策略是共享引用的列，其中包含唯一值以加入表並進行簡單的事務。讓我們考慮與上述相同的例子。

創建JPA項目。所有項目模塊如下所示：

創建實體

在「src」包下創建一個名為「com.tutorialspoint.eclipselink.entity」的包。在給定的包下創建一個名為Staff.java的新Java類。Staff實體類顯示如下：

package com.tutorialspoint.eclipselink.entity;


import java.io.Serializable;
import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.Inheritance;

import javax.persistence.InheritanceType;

import javax.persistence.Table;
@Entity

@Table

@Inheritance( strategy = InheritanceType.JOINED )
public class Staff implements Serializable {
   @Id

   @GeneratedValue( strategy = GenerationType.AUTO )
   private int sid;

   private String sname;
   public Staff( int sid, String sname ) {

      super;

      this.sid = sid;

      this.sname = sname;

   }
   public Staff {

      super;

   }
   public int getSid {

      return sid;

   }
   public void setSid( int sid ) {

      this.sid = sid;

   }
   public String getSname {

      return sname;

   }

public void setSname( String sname ) { this.sname = sname; } }

package com.tutorialspoint.eclipselink.entity;


import javax.persistence.DiscriminatorValue;

import javax.persistence.Entity;
@Entity

@PrimaryKeyJoinColumn(referencedColumnName="sid")
public class TeachingStaff extends Staff {

   private String qualification;

   private String subjectexpertise;
   public TeachingStaff( int sid, String sname, 
   String qualification,String subjectexpertise ) {

      super( sid, sname );

      this.qualification = qualification;

      this.subjectexpertise = subjectexpertise;

   }
   public TeachingStaff {

      super;

   }
   public String getQualification{

      return qualification;

   }
   public void setQualification( String qualification ){

      this.qualification = qualification;

   }
   public String getSubjectexpertise {

      return subjectexpertise;

   }

public void setSubjectexpertise( String subjectexpertise ){ this.subjectexpertise = subjectexpertise; } }

package com.tutorialspoint.eclipselink.entity;


import javax.persistence.DiscriminatorValue;

import javax.persistence.Entity;
@Entity

@PrimaryKeyJoinColumn(referencedColumnName="sid")
public class NonTeachingStaff extends Staff {

   private String areaexpertise;
   public NonTeachingStaff( int sid, String sname, String areaexpertise ) {

      super( sid, sname );

      this.areaexpertise = areaexpertise;

   }
   public NonTeachingStaff {

      super;

   }
   public String getAreaexpertise {

      return areaexpertise;

   }

public void setAreaexpertise( String areaexpertise ) { this.areaexpertise = areaexpertise; } }

persistence.xml中

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


<persistence version = "2.0" xmlns = "http://java.sun.com/xml/ns/persistence"

   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"

   xsi:schemaLocation = "http://java.sun.com/xml/ns/persistence

   http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
   <persistence-unit name = "Eclipselink_JPA" transaction-type = "RESOURCE_LOCAL">

      <class>com.tutorialspoint.eclipselink.entity.Staff</class>

      <class>com.tutorialspoint.eclipselink.entity.NonTeachingStaff</class>

      <class>com.tutorialspoint.eclipselink.entity.TeachingStaff</class>
      <properties>

         <property name = "javax.persistence.jdbc.url" value = "jdbc:mysql://localhost:3306/jpadb"/>

         <property name = "javax.persistence.jdbc.user" value = "root"/>

         <property name = "javax.persistence.jdbc.password" value = "root"/>

         <property name = "javax.persistence.jdbc.driver" value = "com.mysql.jdbc.Driver"/>

         <property name = "eclipselink.logging.level" value = "FINE"/>

         <property name = "eclipselink.ddl-generation" value = "create-tables"/>

      </properties>

</persistence-unit> </persistence>

服務類

在給定的包下創建一個名為SaveClient.java的類來存儲Staff，TeachingStaff和NonTeachingStaff類欄位。然後SaveClient類如下：

package com.tutorialspoint.eclipselink.service;


import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.Persistence;

import com.tutorialspoint.eclipselink.entity.NonTeachingStaff;

import com.tutorialspoint.eclipselink.entity.TeachingStaff;
public class SaveClient {

   public static void main( String[ ] args ) {

      EntityManagerFactory emfactory = Persistence.createEntityManagerFactory( "Eclipselink_JPA" );

      EntityManager entitymanager = emfactory.createEntityManager;

      entitymanager.getTransaction.begin;
      //Teaching staff entity

      TeachingStaff ts1 = new TeachingStaff(1,"Gopal","MSc MEd","Maths");

      TeachingStaff ts2 = new TeachingStaff(2, "Manisha", "BSc BEd", "English");
      //Non-Teaching Staff entity

      NonTeachingStaff nts1 = new NonTeachingStaff(3, "Satish", "Accounts");

      NonTeachingStaff nts2 = new NonTeachingStaff(4, "Krishna", "Office Admin");
      //storing all entities

      entitymanager.persist(ts1);

      entitymanager.persist(ts2);

      entitymanager.persist(nts1);

      entitymanager.persist(nts2);

entitymanager.getTransaction.commit; entitymanager.close; emfactory.close; } }

編譯和執行上述程序後，您將在Eclipse IDE的控制面板中收到通知。輸出檢查MySQL工作台如下：

這裡創建了三個表格，表格格式的員工表格的結果如下所示：

Sid	Dtype	Sname
1	TeachingStaff	Gopal
2	TeachingStaff	Manisha
3	NonTeachingStaff	Satish
4	NonTeachingStaff	Krishna

TeachingStaff表的結果如表格所示：

Sid	Qualification	Subjectexpertise
1	MSC MED	Maths
2	BSC BED	English

在上表中sid是外鍵（參考欄位表單staff表）NonTeachingStaff表的結果如表格所示：

Sid	Areaexpertise
3	Accounts
4	Office Admin

最後，這三個表分別使用它們的欄位創建，SID欄位由所有三個表共享。在員工表SID中是主鍵，在剩餘的（TeachingStaff和NonTeachingStaff）表中SID是外鍵。

每個類策略表

每個類策略的表是為每個子實體創建一個表。工作人員表將被創建，但它將包含空記錄。Staff表的欄位值必須由TeachingStaff和NonTeachingStaff表共享。

讓我們考慮與上述相同的例子。本項目的所有模塊如下所示：

package com.tutorialspoint.eclipselink.entity;


import java.io.Serializable;
import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.Inheritance;

import javax.persistence.InheritanceType;

import javax.persistence.Table;
@Entity

@Table

@Inheritance( strategy = InheritanceType.TABLE_PER_CLASS )
public class Staff implements Serializable {
   @Id

   @GeneratedValue( strategy = GenerationType.AUTO )
   private int sid;

   private String sname;
   public Staff( int sid, String sname ) {

      super;

      this.sid = sid;

      this.sname = sname;

   }
   public Staff {

      super;

   }
   public int getSid {

      return sid;

   }
   public void setSid( int sid ) {

      this.sid = sid;

   }
   public String getSname {

      return sname;

   }

public void setSname( String sname ) { this.sname = sname; } }

package com.tutorialspoint.eclipselink.entity;


import javax.persistence.DiscriminatorValue;

import javax.persistence.Entity;
@Entity

public class TeachingStaff extends Staff {

   private String qualification;

   private String subjectexpertise;
   public TeachingStaff( int sid, String sname, String qualification, String subjectexpertise ) {

      super( sid, sname );

      this.qualification = qualification;

      this.subjectexpertise = subjectexpertise;

   }
   public TeachingStaff {

      super;

   }
   public String getQualification{

      return qualification;

   }
   public void setQualification( String qualification ) {

      this.qualification = qualification;

   }
   public String getSubjectexpertise {

      return subjectexpertise;

   }

public void setSubjectexpertise( String subjectexpertise ){ this.subjectexpertise = subjectexpertise; } }

package com.tutorialspoint.eclipselink.entity;


import javax.persistence.DiscriminatorValue;

import javax.persistence.Entity;
@Entity

public class NonTeachingStaff extends Staff {

   private String areaexpertise;
   public NonTeachingStaff( int sid, String sname, String areaexpertise ) {

      super( sid, sname );

      this.areaexpertise = areaexpertise;

   }
   public NonTeachingStaff {

      super;

   }
   public String getAreaexpertise {

      return areaexpertise;

   }

public void setAreaexpertise( String areaexpertise ) { this.areaexpertise = areaexpertise; } }

<?xml version="1.0" encoding = "UTF-8"?> <persistence version = "2.0" xmlns = "http://java.sun.com/xml/ns/persistence" xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation = "http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">


   <persistence-unit name = "Eclipselink_JPA" transaction-type = "RESOURCE_LOCAL">

      <class>com.tutorialspoint.eclipselink.entity.Staff</class>

      <class>com.tutorialspoint.eclipselink.entity.NonTeachingStaff</class>

      <class>com.tutorialspoint.eclipselink.entity.TeachingStaff</class>
      <properties>

         <property name = "javax.persistence.jdbc.url" value = "jdbc:mysql://localhost:3306/jpadb"/>

         <property name = "javax.persistence.jdbc.user" value = "root"/>

         <property name = "javax.persistence.jdbc.password" value = "root"/>

         <property name = "javax.persistence.jdbc.driver" value = "com.mysql.jdbc.Driver"/>

         <property name = "eclipselink.logging.level" value = "FINE"/>

         <property name = "eclipselink.ddl-generation" value="create-tables"/>

      </properties>

</persistence-unit> </persistence>

package com.tutorialspoint.eclipselink.service;


import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.Persistence;
import com.tutorialspoint.eclipselink.entity.NonTeachingStaff;

import com.tutorialspoint.eclipselink.entity.TeachingStaff;
public class SaveClient {

   public static void main( String[ ] args ) {

      EntityManagerFactory emfactory = Persistence.createEntityManagerFactory( "Eclipselink_JPA" );

      EntityManager entitymanager = emfactory.createEntityManager;

      entitymanager.getTransaction.begin;
      //Teaching staff entity

      TeachingStaff ts1 = new TeachingStaff(1,"Gopal","MSc MEd","Maths");

      TeachingStaff ts2 = new TeachingStaff(2, "Manisha", "BSc BEd", "English");
      //Non-Teaching Staff entity

      NonTeachingStaff nts1 = new NonTeachingStaff(3, "Satish", "Accounts");

      NonTeachingStaff nts2 = new NonTeachingStaff(4, "Krishna", "Office Admin");
      //storing all entities

      entitymanager.persist(ts1);

      entitymanager.persist(ts2);

      entitymanager.persist(nts1);

      entitymanager.persist(nts2);