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Hibernate組件映射

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組件映射是一類具有參考到另一個類的成員變量的映射。我們已經看到，同時有兩個表，並使用在映射文件中的<set>元素這樣的映射。現在我們將使用<component>元素在映射文件和一個單一的表將用於保持包含的類變量裡麵的屬性。

定義RDBMS表：

考慮一個情況下，需要員工記錄存儲在EMPLOYEE表，表有以下結構：

create table EMPLOYEE (
   id INT NOT NULL auto_increment,
   first_name VARCHAR(20) default NULL,
   last_name  VARCHAR(20) default NULL,
   salary     INT  default NULL,
   PRIMARY KEY (id)
);

此外，假設每個雇工將有一個地址，所以在同一個表中添加特定的地址字段，如下所示：

create table EMPLOYEE (
   id INT NOT  NULL auto_increment,
   first_name  VARCHAR(20) default NULL,
   last_name   VARCHAR(20) default NULL,
   salary      INT  default NULL,
   street_name VARCHAR(40) default NULL,
   city_name   VARCHAR(40) default NULL,
   state_name  VARCHAR(40) default NULL,
   zipcode     VARCHAR(10) default NULL,
   PRIMARY KEY (id)
);

定義POJO類：

實現POJO員工類將被用於保存與EMPLOYEE表的對象。

import java.util.*;

public class Employee implements java.io.Serializable {
   private int id;
   private String firstName; 
   private String lastName;   
   private int salary;
   private Address address;

   public Employee() {}
   public Employee(String fname, String lname, 
                   int salary, Address address ) {
      this.firstName = fname;
      this.lastName = lname;
      this.salary = salary;
      this.address = address;
   }
   public int getId() {
      return id;
   }
   public void setId( int id ) {
      this.id = id;
   }
   public String getFirstName() {
      return firstName;
   }
   public void setFirstName( String first_name ) {
      this.firstName = first_name;
   }
   public String getLastName() {
      return lastName;
   }
   public void setLastName( String last_name ) {
      this.lastName = last_name;
   }
   public int getSalary() {
      return salary;
   }
   public void setSalary( int salary ) {
      this.salary = salary;
   }

   public Address getAddress() {
      return address;
   }
   public void setAddress( Address address ) {
      this.address = address;
   }
}

需要定義對應地址有實體地址相關字段到另一個POJO類。

import java.util.*;

public class Address{
   private int id;
   private String street;     
   private String city;     
   private String state;    
   private String zipcode; 

   public Address() {}
   public Address(String street, String city, 
                  String state, String zipcode) {
      this.street = street; 
      this.city = city; 
      this.state = state; 
      this.zipcode = zipcode; 
   }
   public int getId() {
      return id;
   }
   public void setId( int id ) {
      this.id = id;
   }
   public String getStreet() {
      return street;
   }
   public void setStreet( String street ) {
      this.street = street;
   }
   public String getCity() {
      return city;
   }
   public void setCity( String city ) {
      this.city = city;
   }
   public String getState() {
      return state;
   }
   public void setState( String state ) {
      this.state = state;
   }
   public String getZipcode() {
      return zipcode;
   }
   public void setZipcode( String zipcode ) {
      this.zipcode = zipcode;
   }
   
}

定義Hibernate映射文件：

編寫指示Hibernate如何定義的類映射到數據庫表的映射文件。<component>元素將被用來定義規則，對所有與地址表關聯的字段。

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
 "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 

<hibernate-mapping>
   <class name="Employee" table="EMPLOYEE">
      <meta attribute="class-description">
         This class contains the employee detail. 
      </meta>
      <id name="id" type="int" column="id">
         <generator class="native"/>
      </id>
      <component name="address" class="Address">
         <property name="street" column="street_name" type="string"/>
         <property name="city" column="city_name" type="string"/>
         <property name="state" column="state_name" type="string"/>
         <property name="zipcode" column="zipcode" type="string"/>
      </component>
      <property name="firstName" column="first_name" type="string"/>
      <property name="lastName" column="last_name" type="string"/>
      <property name="salary" column="salary" type="int"/>
   </class>

   <class name="Certificate" table="CERTIFICATE">
      <meta attribute="class-description">
         This class contains the certificate records. 
      </meta>
      <id name="id" type="int" column="id">
         <generator class="native"/>
      </id>
      <property name="name" column="certificate_name" type="string"/>
   </class>

</hibernate-mapping>

保存映射文件名的格式為：<classname>.hbm.xml。保存映射文件Employee.hbm.xml。在前麵已經熟悉了大部分的映射細節，但再次看看映射文件中的所有元素：

  • 映射文檔是具有<hibernate-mapping>為對應於每個類對應的2個<class>元素的根元素的XML文檔。

  • <class>元素被用於定義數據庫表從一個Java類特定的映射。Java類名指定使用class元素的name屬性和使用表屬性數據庫表名指定。

  • <meta>元素是可選元素，可以用來創建類的描述。

  • <id>元素映射在類中的唯一ID屬性到數據庫表的主鍵。 id元素的name屬性是指屬性的類和column屬性是指在數據庫表中的列。 type屬性保存了Hibernate映射類型，這種類型的映射將會從Java轉換為SQL數據類型。

  • id元素內的<generator>元素被用來自動生成的主鍵值。將生成元素的class屬性設置為原生讓Hibernate拾取無論是identity，sequence還是hilo的算法來創建主鍵根據底層數據庫的支持能力。

  • <property>元素用於一個Java類的屬性映射到數據庫表中的列。元素的name屬性是指屬性的類和column屬性是指在數據庫表中的列。 type屬性保存了Hibernate映射類型，這種類型的映射將會從Java轉換為SQL數據類型。

  • <component>元素設置地址類的內部Employee類的不同屬性的存在。

創建應用程序類：

最後，創建應用程序類的main（）方法來運行應用程序。使用這個應用程序，以節省一些員工的記錄關聯證書，然後將應用CRUD操作記錄。

import java.util.*;
 
import org.hibernate.HibernateException; 
import org.hibernate.Session; 
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class ManageEmployee {
   private static SessionFactory factory; 
   public static void main(String[] args) {
      try{
         factory = new Configuration().configure().buildSessionFactory();
      }catch (Throwable ex) { 
         System.err.println("Failed to create sessionFactory object." + ex);
         throw new ExceptionInInitializerError(ex); 
      }
      ManageEmployee ME = new ManageEmployee();

      /* Let us have one address object */
      Address address1 = ME.addAddress("Kondapur","Hyderabad","AP","532");

      /* Add employee records in the database */
      Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, address1);

      /* Let us have another address object */
      Address address2 = ME.addAddress("Saharanpur","Ambehta","UP","111");
  
    /* Add another employee record in the database */
      Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, address2);

      /* List down all the employees */
      ME.listEmployees();

      /* Update employee's salary records */
      ME.updateEmployee(empID1, 5000);

      /* List down all the employees */
      ME.listEmployees();

   }

   /* Method to add an address record in the database */
   public Address addAddress(String street, String city, 
                             String state, String zipcode) {
      Session session = factory.openSession();
      Transaction tx = null;
      Integer addressID = null;
      Address address = null;
      try{
         tx = session.beginTransaction();
         address = new Address(street, city, state, zipcode);
         addressID = (Integer) session.save(address); 
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      }finally {
         session.close(); 
      }
      return address;
   }

   /* Method to add an employee record in the database */
   public Integer addEmployee(String fname, String lname, 
                              int salary, Address address){
      Session session = factory.openSession();
      Transaction tx = null;
      Integer employeeID = null;
      try{
         tx = session.beginTransaction();
         Employee employee = new Employee(fname, lname, salary, address);
         employeeID = (Integer) session.save(employee); 
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      }finally {
         session.close(); 
      }
      return employeeID;
   }

   /* Method to list all the employees detail */
   public void listEmployees( ){
      Session session = factory.openSession();
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         List employees = session.createQuery("FROM Employee").list(); 
         for (Iterator iterator = 
                           employees.iterator(); iterator.hasNext();){
            Employee employee = (Employee) iterator.next(); 
            System.out.print("First Name: " + employee.getFirstName()); 
            System.out.print("  Last Name: " + employee.getLastName()); 
            System.out.println("  Salary: " + employee.getSalary());
            Address add = employee.getAddress();
            System.out.println("Address ");
            System.out.println("	Street: " +  add.getStreet());
            System.out.println("	City: " + add.getCity());
            System.out.println("	State: " + add.getState());
            System.out.println("	Zipcode: " + add.getZipcode());
         }
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      }finally {
         session.close(); 
      }
   }
   /* Method to update salary for an employee */
   public void updateEmployee(Integer EmployeeID, int salary ){
      Session session = factory.openSession();
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         Employee employee = 
                    (Employee)session.get(Employee.class, EmployeeID); 
         employee.setSalary( salary );
         session.update(employee);
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      }finally {
         session.close(); 
      }
   }
}

編譯和執行：

下麵是步驟來編譯並運行上述應用程序。請確保您已在進行的編譯和執行之前，適當地設置PATH和CLASSPATH。

  • 創建hibernate.cfg.xml配置文件。

  • 創建Employee.hbm.xml映射文件，如上圖所示。

  • 創建Employee.java源文件，如上圖所示，並編譯它。

  • 創建ManageEmployee.java源文件，如上圖所示，並編譯它。

  • 執行ManageEmployee二進製文件來運行程序。

在屏幕上獲得以下結果，並同時記錄會在EMPLOYEE表中創建。

$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........

First Name: Manoj  Last Name: Kumar  Salary: 4000
Address
        Street: Kondapur
        City: Hyderabad
        State: AP
        Zipcode: 532
First Name: Dilip  Last Name: Kumar  Salary: 3000
Address
        Street: Saharanpur
        City: Ambehta
        State: UP
        Zipcode: 111
First Name: Manoj  Last Name: Kumar  Salary: 5000
Address
        Street: Kondapur
        City: Hyderabad
        State: AP
        Zipcode: 532
First Name: Dilip  Last Name: Kumar  Salary: 3000
Address
        Street: Saharanpur
        City: Ambehta
        State: UP
        Zipcode: 111

如果檢查EMPLOYEE表，它應該已記錄下：

mysql> select id, first_name,salary, street_name, state_name from EMPLOYEE;
+----+------------+--------+-------------+------------+
| id | first_name | salary | street_name | state_name |
+----+------------+--------+-------------+------------+
|  1 | Manoj      |   5000 | Kondapur    | AP         |
|  2 | Dilip      |   3000 | Saharanpur  | UP         |
+----+------------+--------+-------------+------------+
2 rows in set (0.00 sec)

mysql>


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