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) );
创建对应的实体:
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集合中元素不重复。是否重复,是通过hashCode和equals方法进行比较的。
hibernate主配置文件的配置如下:
<?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>
测试:
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中添加了两个MCA。运行结果如下:
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只出现了一次!注意Certificate中hashCode和equals的作用。
【LeetCode】Climbing Stairs,布布扣,bubuko.com
时间: 2024-10-23 21:02:25