舉例講授Java的Hibernate框架中的多對一和一對多映照。本站提示廣大學習愛好者：（舉例講授Java的Hibernate框架中的多對一和一對多映照）文章只能為提供參考，不一定能成為您想要的結果。以下是舉例講授Java的Hibernate框架中的多對一和一對多映照正文
多對一（Many-to-One）映照
多對一（many-to-one）聯系關系是最多見的聯系關系關系，個中一個對象可以與多個對象相干聯。例如，一個雷同的地址對象可以與多個雇員的對象相干聯。
界說RDBMS表：
斟酌一個情形，我們須要員工記載存儲在EMPLOYEE表，將有以下構造：
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, address INT NOT NULL, PRIMARY KEY (id) );
另外，很多員工都可以有雷同的地址，所以這類聯系關系可使用很多一對一的聯系關系出現。我們將存儲地址相干的信息在一個零丁的表，該表具有以下構造：
create table ADDRESS ( id INT NOT NULL auto_increment, 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) );
同時創立RBDMS表，並讓他們預備下一個完成。
界說POJO類：
讓我們完成一個POJO類員工將被用於保留與EMPLOYEE表的對象和其地址類型的變量。
import java.util.*;
public class Employee{
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;
}
}
我們須要界說響應的地址表，如許地址對象可以存儲和檢索到地址表中的另外一個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;
}
}
界說Hibernate映照文件：
開辟我們的映照文件，可指導Hibernate若何界說的類映照到數據庫表。<many-to-one>停止元素將被用來界說規矩樹立Employee和Address實體之間的多對一關系。
<?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>
<property name="firstName" column="first_name" type="string"/>
<property name="lastName" column="last_name" type="string"/>
<property name="salary" column="salary" type="int"/>
<many-to-one name="address" column="address"
class="Address" not-null="true"/>
</class>
<class name="Address" table="ADDRESS">
<meta attribute="class-description">
This class contains the address detail.
</meta>
<id name="id" type="int" column="id">
<generator class="native"/>
</id>
<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"/>
</class>
</hibernate-mapping>
應當保留的映照文件中的格局<classname>.hbm.xml。保留映照文件中的文件Employee.hbm.xml。曾經熟習了年夜部門的映照細節，但讓我們再次看看映照文件中的一切元素：
映照文檔是具有<hibernate-mapping>為對應於每個類包括2個<class>元素的根元素的XML文檔。
<class>元素被用於界說數據庫表從一個Java類特定的映照。 Java類名指定應用class元素的name屬性和應用表屬性數據庫表名指定。
<meta>元素是可選元素，可以用來創立類的描寫。
<id>元素映照在類中的獨一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屬性保留了Hibernate映照類型，這類類型的映照將會從Java轉換為SQL數據類型。
id元素內<generator>元素被用來主動生成的主鍵值。將生成元素class屬性設置為原生讓Hibernate拾取不管是identity，sequence或許hilo的算法來創立主鍵依據底層數據庫的支撐才能。
<property>元素用於一個Java類的屬性映照到數據庫表中的列。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屬性保留了Hibernate映照類型，這類類型的映照將會從Java轉換為SQL數據類型。
<many-to-one>停止元素是用來設置EMPLOYEE和地址的實體之間的關系。name屬性被設置為在父類中界說的變量，在我們的情形下，它是地址。列屬性用於在父表EMPLOYEE集的列名。
最初，我們將創立運用法式類的main（）辦法來運轉運用法式。我們將應用這個運用法式，以節儉一些employee連同的記載他們的地址，然後我們將請求CRUD操作上的記載。
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 address = ME.addAddress("Kondapur","Hyderabad","AP","532");
/* Add employee records in the database */
Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, address);
/* Add another employee record in the database */
Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, address);
/* List down all the employees */
ME.listEmployees();
/* Update employee's salary records */
ME.updateEmployee(empID1, 5000);
/* Delete an employee from the database */
ME.deleteEmployee(empID2);
/* 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();
}
}
/* Method to delete an employee from the records */
public void deleteEmployee(Integer EmployeeID){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
session.delete(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
}
編譯和履行：
上面是步調來編譯並運轉上述運用法式。請確保已在停止的編譯和履行之前，恰當地設置PATH和CLASSPATH。
在屏幕上取得以下成果，並同時記載會在員工和地址表創立。
$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: Kondapur
City: Hyderabad
State: AP
Zipcode: 532
First Name: Manoj Last Name: Kumar Salary: 5000
Address
Street: Kondapur
City: Hyderabad
State: AP
Zipcode: 532
假如檢討員工和地址表，就應當記載下了：
mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+---------+ | id | first_name | last_name | salary | address | +----+------------+-----------+--------+---------+ | 1 | Manoj | Kumar | 5000 | 5 | +----+------------+-----------+--------+---------+ 1 row in set (0.00 sec)
mysql> select * from ADDRESS;
+----+-------------+-----------+------------+---------+ | id | street_name | city_name | state_name | zipcode | +----+-------------+-----------+------------+---------+ | 1 | Kondapur | Hyderabad | AP | 532 | +----+-------------+-----------+------------+---------+ 1 row in set (0.00 sec)
一對多（One-to-Many）映照
一對多的映照可使用一組Java聚集不包括任何反復的元從來完成。我們曾經看到了若何設置映照聚集在Hibernate中，所以假如你曾經學會了聚集（Set）映照，那末一切設置可用於一對多的映照。
聚集被映照到與映照表中<set>元素，並java.util.HashSet中初始化。您可使用Set聚集在類中，有一個聚集中不須要反復的元素。
RDBMS表與POJO類我們仍然采取下面例子中界說好的，
界說Hibernate映照文件：
讓我們指導Hibernate若何界說的類映照到數據庫表的映照文件。
<?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>
<set name="certificates" cascade="all">
<key column="employee_id"/>
<one-to-many class="Certificate"/>
</set>
<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>
應當保留的映照文件中的格局<classname>.hbm.xml。我們保留映照文件中的文件Employee.hbm.xml。你曾經熟習了年夜部門的映照細節，但讓我們再次看看映照文件中的一切元素：
映照文檔是具有<hibernate-mapping>為對應於每個類包括2個<class>元素的根元素的XML文檔。
<class>元素被用於界說數據庫表從一個Java類特定的映照。 Java類名指定應用class元素的name屬性和應用表屬性數據庫表名指定。
<meta>元素是可選元素，可以用來創立類的描寫。
<id>元素映照在類中的獨一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屬性保留了Hibernate映照類型，這類類型的映照將會從Java轉換為SQL數據類型。
id元素內的<generator>元素被用來主動生成的主鍵值。將生成元素的class屬性設置為原生讓Hibernate拾取identity，sequence或許hilo中的算法來創立主鍵依據底層數據庫的支撐才能。
<property>元素用於一個Java類的屬性映照到數據庫表中的列。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屬性保留了Hibernate映照類型，這類類型的映照將會從Java轉換為SQL數據類型。
<set>元素設置證書和Employee類之間的關系。我們應用cascade屬性中<set>元從來告知Hibernate來保留證書的對象，同時為Employee對象。 name屬性被設置為在父類中界說的變量集，在我們的例子是證書。關於每組變量，我們須要界說在映照文件中零丁的一組元素。
<key>元素是包括外鍵的父對象，即在證書表中的列。表EMPLOYEE。
<one-to-many>元素表現一個Employee對象觸及到許多證書的對象。
創立運用法式類：
最初，我們將創立運用法式類的main（）辦法來運轉運用法式。我們將應用這個運用法式，以節儉一些員工連同記載證書，然後我們將運用上CRUD操作記載。
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 a set of certificates for the first employee */
HashSet set1 = new HashSet();
set1.add(new Certificate("MCA"));
set1.add(new Certificate("MBA"));
set1.add(new Certificate("PMP"));
/* Add employee records in the database */
Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);
/* Another set of certificates for the second employee */
HashSet set2 = new HashSet();
set2.add(new Certificate("BCA"));
set2.add(new Certificate("BA"));
/* Add another employee record in the database */
Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);
/* List down all the employees */
ME.listEmployees();
/* Update employee's salary records */
ME.updateEmployee(empID1, 5000);
/* Delete an employee from the database */
ME.deleteEmployee(empID2);
/* List down all the employees */
ME.listEmployees();
}
/* Method to add an employee record in the database */
public Integer addEmployee(String fname, String lname,
int salary, Set cert){
Session session = factory.openSession();
Transaction tx = null;
Integer employeeID = null;
try{
tx = session.beginTransaction();
Employee employee = new Employee(fname, lname, salary);
employee.setCertificates(cert);
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 iterator1 =
employees.iterator(); iterator1.hasNext();){
Employee employee = (Employee) iterator1.next();
System.out.print("First Name: " + employee.getFirstName());
System.out.print(" Last Name: " + employee.getLastName());
System.out.println(" Salary: " + employee.getSalary());
Set certificates = employee.getCertificates();
for (Iterator iterator2 =
certificates.iterator(); iterator2.hasNext();){
Certificate certName = (Certificate) iterator2.next();
System.out.println("Certificate: " + certName.getName());
}
}
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();
}
}
/* Method to delete an employee from the records */
public void deleteEmployee(Integer EmployeeID){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
session.delete(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
}
編譯和履行：
$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........ First Name: Manoj Last Name: Kumar Salary: 4000 Certificate: MBA Certificate: PMP Certificate: MCA First Name: Dilip Last Name: Kumar Salary: 3000 Certificate: BCA Certificate: BA First Name: Manoj Last Name: Kumar Salary: 5000 Certificate: MBA Certificate: PMP Certificate: MCA
假如檢討員工和證書表，就應當記載下了：
mysql> select * from employee;
+----+------------+-----------+--------+ | id | first_name | last_name | salary | +----+------------+-----------+--------+ | 1 | Manoj | Kumar | 5000 | +----+------------+-----------+--------+ 1 row in set (0.00 sec)
mysql> select * from certificate;
+----+------------------+-------------+ | id | certificate_name | employee_id | +----+------------------+-------------+ | 1 | MBA | 1 | | 2 | PMP | 1 | | 3 | MCA | 1 | +----+------------------+-------------+ 3 rows in set (0.00 sec)
