Set集合的配置

数据表的创建:表关系一个员工拥有多个身份

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) );
create table CERTIFICATE ( id INT NOT NULL auto_increment, certificate_name VARCHAR(30) default NULL, employee_id INT default NULL, PRIMARY KEY (id) );

创建相应的实体:

package com.study01;

import java.util.Set;

public class Employee {
private int id;
private String firstName;
private String lastName;
private int salary;
private Set certificates; public Employee() {
} public Employee(String fname, String lname, int salary) {
this.firstName = fname;
this.lastName = lname;
this.salary = salary;
} public int getId() {
return id;
} public void setId(int id) {
this.id = id;
} public String getFirstName() {
return firstName;
} public void setFirstName(String firstName) {
this.firstName = firstName;
} public String getLastName() {
return lastName;
} public void setLastName(String lastName) {
this.lastName = lastName;
} public int getSalary() {
return salary;
} public void setSalary(int salary) {
this.salary = salary;
} public Set getCertificates() {
return certificates;
} public void setCertificates(Set certificates) {
this.certificates = certificates;
} }
package com.study01;

public class Certificate {
private int id;
private String name; public Certificate() {
} public Certificate(String name) {
this.name = name;
} public int getId() {
return id;
} public void setId(int id) {
this.id = id;
} public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public boolean equals(Object obj) {
if (obj == null)
return false;
if (!this.getClass().equals(obj.getClass()))
return false;
Certificate obj2 = (Certificate) obj;
//if ((this.id == obj2.getId()) && (this.name.equals(obj2.getName()))) {
// return true;
//}
if(this.name.equals(obj2.getName())) return true;
return false;
} public int hashCode() {
int tmp = 0;
tmp = (id + name).hashCode();
return tmp;
}
}

注意这里对equals和hashCode方法进行了重写。set集合中元素不反复。是否反复,是通过hashCode和equals方法进行比較的。

hibernate主配置文件的配置例如以下:

<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-configuration SYSTEM "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.dialect"> org.hibernate.dialect.MySQLDialect </property>
<property name="hibernate.connection.driver_class"> com.mysql.jdbc.Driver </property> <!-- Assume test is the database name -->
<property name="hibernate.connection.url"> jdbc:mysql://localhost/test </property>
<property name="hibernate.connection.username"> root </property>
<property name="hibernate.connection.password"> 253503125 </property> <!-- List of XML mapping files -->
<mapping resource="com/study01/Employee.hbm.xml" />
<mapping resource="com/study01/Certificate.hbm.xml" />
</session-factory>
</hibernate-configuration>

映射文件的配置:

<?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 package="com.study01">
<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> </hibernate-mapping>
<?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 package="com.study01"> <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>

測试:

package com.study01;

import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set; import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
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();
HashSet set1 = new HashSet();
set1.add(new Certificate("MCA"));
set1.add(new Certificate("MBA"));
set1.add(new Certificate("PMP"));
set1.add(new Certificate("MCA")); /* Add employee records in the database */
Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1); HashSet set2 = new HashSet();
set2.add(new Certificate("BCA"));
set2.add(new Certificate("BA"));
Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2); 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 */
System.out.println("======================");
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();
}
}
}

注意在Certificate中加入�了两个MCA。执行结果例如以下:

First Name: Manoj Last Name: Kumar Salary: 4000
Certificate: PMP
Certificate: MCA
Certificate: MBA
First Name: Dilip Last Name: Kumar Salary: 3000
Certificate: BCA
Certificate: BA
======================
First Name: Manoj Last Name: Kumar Salary: 5000
Certificate: PMP
Certificate: MCA
Certificate: MBA

MCA仅仅出现了一次!注意Certificate中hashCode和equals的作用。

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