Hibernate 框架总结(四)：多张表的关联映射

Hibernate 框架总结(一)：简单开发

Hibernate 框架总结(二)：session的获取方式及hibernate对象的生命周期

Hibernate 框架总结(三)：主键的生成策略

Hibernate 框架总结(五)：查询

Hibernate 框架总结(六)：缓存机制

表与表之间的关系

存在三种关系

一对一：丈夫——妻子， 学生——学生证

一对多：学生——班级， 皇帝——大臣

多对多：学生——课程， 学生——老师

配置关系映射的时候，无论是什么关系，要保证你中有我，我中有你的思想

一对一

开发一个husband实体类和一个wife实体类,两个表中都有name和age属性，两个类中互相拥有，就是Husband类中要有一个wife属性，Wife类中要有一个husband属性

两张表拥有关系，就肯定要有一张表来维系关系，通常来说多的哪一方来维系，一对一的关系中哪一方来维护都行，这里让husband来维护关系，既然husband来维系关系，那么husband表中肯定要增加一列，存放wife的id，而wife只需交给husband的来维护就行

Husband实体类：

package sdibt.fly.entity;


import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
/**
 * 丈夫实体类
 * @author lxj
 *
 */
@Entity
@Table(name="tb_husband",schema="hibernatedb")
public class Husband {
	
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	private String name;//姓名
	private int age;//年龄
	
	//维护的一方即使是一对一的关系，这里也要写出ManyToOne
	@ManyToOne
	@JoinColumn(name="wid",unique=true)//在表中增加一列，而且值是唯一的
	private Wife wife;
	
	public Wife getWife() {
		return wife;
	}
	public void setWife(Wife wife) {
		this.wife = wife;
	}
	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 int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
}

Wife实体类

package sdibt.fly.entity;


import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;


/**
 * 妻子实体类
 * @author lxj
 *
 */
@Entity
@Table(name="tb_wife",schema="hibernatedb")
public class Wife {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	private String name;//姓名
	private int age;//年龄
	
	//交给Husband中的Wife属性来维护，名字不能写错
	@OneToOne(mappedBy="wife")
	private Husband husband;
	
	
	public Husband getHusband() {
		return husband;
	}
	public void setHusband(Husband husband) {
		this.husband = husband;
	}
	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 int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	
	
}

一对多

班级与学生之间就是一对多的关系，一个班级可以有多个学生，但是一个学生只能对应一个班级，所有让学生表来维系关系，因为班级里可以有很多学生，所有Classes里的学生属性要是一个集合

Student类：

package sdibt.fly.entity;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
@Entity
@Table(name="tb_student",schema="hibernatedb")
public class Student {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	private String stuName;
	private int age;
	//多对一，多的一方维系关系
	@ManyToOne
	@JoinColumn(name="class_id")
	private Classes classes;
	
	
	public Classes getClasses() {
		return classes;
	}
	public void setClasses(Classes classes) {
		this.classes = classes;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getStuName() {
		return stuName;
	}
	public void setStuName(String stuName) {
		this.stuName = stuName;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
		
}

Classes类：

package sdibt.fly.entity;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="tb_classes",schema="hibernatedb")
public class Classes {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	private String clsName;
	//一对多关系，存放sutdent集合
	@OneToMany(mappedBy="classes")
	private List students=new ArrayList();
	
	
	public List getStudents() {
		return students;
	}
	public void setStudents(List students) {
		this.students = students;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getClsName() {
		return clsName;
	}
	public void setClsName(String clsName) {
		this.clsName = clsName;
	}

}

多对多

学生和老师之间是多对多关系，一个学生可以有多个老师，一个老师也可以有多个学生，当产生多对多关系时，就要创建一张表来维护两者之间的关，对student进行改动，增加一个teacher属性，因为Student表经常变化，所有维系关系也交给Student

Student类：

package sdibt.fly.entity;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
@Entity
@Table(name="tb_student",schema="hibernatedb")
public class Student {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	private String stuName;
	private int age;
	
	@ManyToOne
	@JoinColumn(name="class_id")
	private Classes classes;//班级
	
	@ManyToMany
	//增加一张表，维护老师，学生之间的关系
		@JoinTable(
				name="st",//中间表的名字
				schema="hibernatedb",//中间表属于哪个数据库
				//关联当前表的外键名
				joinColumns=@JoinColumn(name="sid"),
				//关联对方表的外键名
				inverseJoinColumns=@JoinColumn(name="tid")
				)
	private List teachers=new ArrayList();//老师
	
	
	public List getTeachers() {
		return teachers;
	}
	public void setTeachers(List teachers) {
		this.teachers = teachers;
	}
	public Classes getClasses() {
		return classes;
	}
	public void setClasses(Classes classes) {
		this.classes = classes;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getStuName() {
		return stuName;
	}
	public void setStuName(String stuName) {
		this.stuName = stuName;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}	
	
}

Teacher类：

package sdibt.fly.entity;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name="tb_teacher",schema="hibernatedb")
public class Teacher {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	private String tName;
	
	//交给学生表来维系关系
	@ManyToMany(mappedBy="teachers")
	
	private List students=new ArrayList();
		
	public List getStudents() {
		return students;
	}
	public void setStudents(List students) {
		this.students = students;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String gettName() {
		return tName;
	}
	public void settName(String tName) {
		this.tName = tName;
	}	
}

生成的中间表：