mysql中间关系表建立联合索引 mysql关联关系

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jkfox 2024-06-19 12:33:52

文章标签 mysql中间关系表建立联合索引 java ssh hibernate mysql 文章分类 MySQL 数据库

一对多关联关系映射

一对多映射关系是由“多"的一方指向”一“的一方。在表示”多“的一方数据表中增加一个外键，来指向”一“的一方的数据表，”一“的一方作为主表，而"多”的一方作为从表。

下面以客户和订单的关联关系来讲解。

首先是建立一个实体类Customer，其中包括客户属性id和name,Set集合orders是订单集合，表示一个客户有多个订单。

package cn.bruceluo.domain;

import java.util.HashSet;
import java.util.Set;

public class Customer {
	private Integer id;
	private String name;
	//orders是集合，是对多的实体类的对象的集合,多个订单
	private Set<Order> orders=new HashSet<Order>();
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Set<Order> getOrders() {
		return orders;
	}
	public void setOrders(Set<Order> orders) {
		this.orders = orders;
	}
	
	
}

接着是order类的创建，其中包括订单的属性id、address和price

package cn.bruceluo.domain;

public class Order {
	private Integer id;
	private String address;
	private Integer price;
	//多的一方有对一的一方对象的引用，多个订单可以是一个人下
	private Customer customer;
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	public Integer getPrice() {
		return price;
	}
	public void setPrice(Integer price) {
		this.price = price;
	}
	public Customer getCustomer() {
		return customer;
	}
	public void setCustomer(Customer customer) {
		this.customer = customer;
	}
	
}

完成类Customer和Order的创建后是创建他们的映射文件 Customer.hbm.xml和Order.hbm.xml,我这里使用了hibernate tools来创建，进行了适当的修改。

Customer.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-10-28 19:57:39 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="cn.bruceluo.domain.Customer" >
        <id name="id" >
            <generator class="native" />
        </id>
        <property name="name" length="20"/>
      
        <!-- 配置了一个set元素 ,级联操作为all表示所有情况下均进行关联操作-->
        <set name="orders"  cascade="all" >
            <key>
            	<!-- 外键取名cid -->
                <column name="CID" />
            </key>
            <one-to-many class="cn.bruceluo.domain.Order" />
        </set>
    </class>
</hibernate-mapping>

Order.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-10-28 19:57:39 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="cn.bruceluo.domain.Order" table="orders">
        <id name="id" >
            <generator class="native" />
        </id>
        <property name="address" length="50" />
        <property name="price" />

        <!-- 配置一个many-to-one -->
        <many-to-one name="customer" class="cn.bruceluo.domain.Customer" column="cid"/>
            
        
    </class>
</hibernate-mapping>

接着是hibernate.cfg.xml配置文件的创建并添加 Customer.hbm.xml和Order.hbm.xml映射文件信息。另外我这里使用了<property name="hibernate.hbm2dd.auto" >update</property来进行自动建表。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
                                         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
 <session-factory>
  <property name="hibernate.dialect">
    org.hibernate.dialect.MySQLInnoDBDialect
    </property>
    <property name="hibernate.connection.driver_class">
    com.mysql.jdbc.Driver
    </property>
    <property name="hibernate.hbm2dd.auto" >update</property>
    <property name="hibernate.connection.username">
    root
    </property>
    <property name="hibernate.connection.password">
    </property>
    <property name="hibernate.show_sql">true</property>
    <property name="format_sql">true</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8</property>
  <mapping resource="cn/bruceluo/domain/Customer.hbm.xml"/>
  <mapping resource="cn/bruceluo/domain/Order.hbm.xml"/>
 </session-factory>
</hibernate-configuration>

配置好了，下面创建一个测试类One2ManyTest

package cn.bruceluo.test;

import static org.junit.Assert.*;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import cn.bruceluo.domain.Customer;
import cn.bruceluo.domain.Order;
import cn.bruceluo.util.HibernateUtil;

public class One2ManyTest {

	@Test
	public void testInsert() {
		//1.得到session
		Session session =HibernateUtil.getSession();
		//2.开启事务
		session.beginTransaction();
		//3.操作:插入操作
		//3.1 创建一个客户，给客户属性赋值
		Customer c=new Customer();
		c.setName("bruceluo");
		//3.2 创建两个订单
		Order order1=new Order();
		order1.setAddress("北京");
		order1.setPrice(1000);
		Order order2=new Order();
		order2.setAddress("上海");
		order2.setPrice(100);
		//3.3  描述关系--客户拥有多个订单
		c.getOrders().add(order2);
		c.getOrders().add(order1);
		//4.提交事务
		session.save(c);
		session.getTransaction().commit();
		//5.关闭资源
		session.close();
	}

}

还有一点是我们要建立一个HibernateUtils的工具类来提供Session对象来防止产生过多的Session Factory实例

package cn.bruceluo.util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
	private static final Configuration config;
	private static final SessionFactory factory;
	static{
		config=new Configuration().configure();
		System.out.println(config);
		factory = config.buildSessionFactory();
	}
	public static Session getSession(){
		return factory.openSession();
	}
}

运行效果

mysql中间关系表建立联合索引 mysql关联关系_mysql中间关系表建立联合索引

多对多关联关系映射

多对多关联关系映射我们使用学生和课程的关联关系来讲解。Student类和Course类与前面Customer和Order类基本相同，属性有所改变而已。

Student.java

package cn.bruceluo.domain;

import java.util.HashSet;
import java.util.Set;

public class Student {
	private Integer id;
	private String sname;
	private Set<Course> courses=new HashSet<Course>();
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	
	public Set<Course> getCourses() {
		return courses;
	}
	public void setCourses(Set<Course> courses) {
		this.courses = courses;
	}
	public String getSname() {
		return sname;
	}
	public void setSname(String sname) {
		this.sname = sname;
	}
	
}

Course.java

package cn.bruceluo.domain;

import java.util.HashSet;
import java.util.Set;

public class Course {
	private Integer id;
	private String cname;
	private Set<Student> students=new HashSet<Student>();
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	
	
	public Set<Student> getStudents() {
		return students;
	}
	public void setStudents(Set<Student> students) {
		this.students = students;
	}
	public String getCname() {
		return cname;
	}
	public void setCname(String cname) {
		this.cname = cname;
	}
	
}

配置文件Student.hbm.xml和Course.hbm.xml与一对多配置方式不同的是<set>标签多了个table属性，这个属性表示中间表的名称我这里是s_c,<key>标签的column属性用于描述student表在中间表外键的名称，在<many-to-many>标签的column属性用于描述course课程表在中间表中的列名。

Student.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-11-1 22:26:40 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="cn.bruceluo.domain.Student" table="student">
        <id name="id" >
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="sname" >
            
        </property>
        <set name="courses" table="s_c"  cascade="all">
            <key>
                <column name="sid" />
            </key>
            <many-to-many class="cn.bruceluo.domain.Course" column="cid"/>
        </set>
    </class>
</hibernate-mapping>

Course.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2018-11-1 22:26:40 by Hibernate Tools 3.5.0.Final -->
<hibernate-mapping>
    <class name="cn.bruceluo.domain.Course" table="course">
        <id name="id" >
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="cname" >
            
        </property>
        <set name="students" table="s_c" >
            <key>
                <column name="cid" />
            </key>
            <many-to-many class="cn.bruceluo.domain.Student" column="sid"/>
        </set>
    </class>
</hibernate-mapping>

在上面的hibernate.cfg.xml中添加Student类和Course类的映射文件信息。

<mapping resource="cn/bruceluo/domain/Student.hbm.xml"/>
  <mapping resource="cn/bruceluo/domain/Course.hbm.xml"/>

测试类Many2ManyTest的创建。

package cn.bruceluo.test;

import static org.junit.Assert.*;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import cn.bruceluo.domain.Course;
import cn.bruceluo.domain.Customer;
import cn.bruceluo.domain.Order;
import cn.bruceluo.domain.Student;
import cn.bruceluo.util.HibernateUtil;

public class Many2ManyTest {

	@Test
	public void testInsert() {
		//1.得到session
		Session session =HibernateUtil.getSession();
		//2.开启事务
		Transaction transaction=session.beginTransaction();
		//3.操作:插入操作
		Student s1=new Student();
		Student s2=new Student();
		s1.setSname("bruceluo");
		s2.setSname("bruceluo");
		Course c1=new Course();
		Course c2=new Course();
		c1.setCname("JAVA");
		c2.setCname("PHP");
		
		//主控方关联关系
		s1.getCourses().add(c1);
		s1.getCourses().add(c2);
		s2.getCourses().add(c1);
		s2.getCourses().add(c2);
		//4.提交事务
		session.save(s1);
		session.save(s2);
		
		session.getTransaction().commit();
		//5.关闭资源
		session.close();
	}

}

测试结果

mysql中间关系表建立联合索引 mysql关联关系_hibernate_02