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Mybatis和Hibernate的映射关系差不多，都有一对一，一对多，多对多，但其实现方式却不同,mybatis主要还是以sql语句为主，而hibernate以映射文件onetoone进行配置相应的属性。

一对一

我们以学生和身份证为例子

创建实体类Card

package cn.qblank.one2one;public class Card {	private Integer id;	private String num;		public Integer getId() {		return id;	}	public void setId(Integer id) {		this.id = id;	}	public String getNum() {		return num;	}	public void setNum(String num) {		this.num = num;	}		@Override	public String toString() {		return "Card [id=" + id + ", num=" + num + "]";	}	}

Student类

package cn.qblank.one2one;public class Student {	private Integer id;	private String name;	private Card card;		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 Card getCard() {		return card;	}	public void setCard(Card card) {		this.card = card;	}		@Override	public String toString() {		return "Student [id=" + id + ", name=" + name + ", card=" + card + "]";	}}

在数据库中创建对应的表

-- 创建学生表CREATE TABLE t_student(	sid INT,	sname VARCHAR(20),	scid INT)-- 创建身份证表CREATE TABLE t_card(	cid INT,	cnum VARCHAR(20))

创建对应的映射文件

StudentMapper.xml

   
   	
    		
     		
     		
     		
     	
    		
    	
    		SELECT s.sid,s.sname,c.cnum 		FROM t_student s 		INNER JOIN t_card c 		ON s.scid = c.cid		AND s.sid = #{id};		
    	
    		SELECT s.sid,s.sname,c.cnum		FROM t_student s INNER JOIN t_card c		ON s.scid = c.cid		AND s.sname = #{name};	
   

CardMapper.xml

将其配置到主配置文件mybatis.xml文件中

然后在StudentCardDao类中写封装对应的方法

/** * 查询1号学生的信息 * @param id */public Student findById(int id) throws Exception {	SqlSession sqlSession = null;	try {		sqlSession = MybatisUtil.getSqlSession();		return sqlSession.selectOne(Student.class.getName() + ".findById",id);			} catch (Exception e) {		e.printStackTrace();		throw e;	} finally {		MybatisUtil.closeSqlSession();	}}/** * 通过姓名查学生信息 * @param name * @return * @throws Exception */public Student findByName(String name) throws Exception{	SqlSession sqlSession = null;	try {		sqlSession = MybatisUtil.getSqlSession();		return sqlSession.selectOne(Student.class.getName() + ".findByName",name);	} catch (Exception e) {		e.printStackTrace();		throw e;	} finally {		MybatisUtil.closeSqlSession();	}}

一对多

以班级和学生来做例子

创建实体类Student和Grade

Student类

package cn.qblank.one2many;/** * 学生 * @author Administrator */public class Student {	private Integer id;	private String name;	private Grade grade;		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 Grade getGrade() {		return grade;	}	public void setGrade(Grade grade) {		this.grade = grade;	}	}

Grade类

package cn.qblank.one2many;import java.util.ArrayList;import java.util.List;/** * 班级 * @author Administrator */public class Grade {	private Integer id;	private String name;	private List
   
     stuList = new ArrayList<>();	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 List
    
      getStuList() {		return stuList;	}	public void setStuList(List
     
       stuList) {		this.stuList = stuList;	}}
     
    
   

创建对应表

-- 班级CREATE TABLE t_grades(	gid INT(5) PRIMARY KEY,	gname VARCHAR(10)	);-- 学生CREATE TABLE t_stu(	sid INT(5) PRIMARY KEY,	sname VARCHAR(10),		sgid INT(5),	CONSTRAINT sgid_fk FOREIGN KEY(sgid) REFERENCES t_grades(gid));

创建对应映射文件StudentMapper.xml和GrapeMapper.xml

StudentMapper.xml

   
   	
    		
     		
     	
    		
    	
    		SELECT s.sid,s.sname		FROM t_stu s INNER JOIN t_grades g		ON s.sgid = g.gid		AND g.gname = #{name};	
   

GradeMapper.xml

   
   	
    		
     		
     	
    		
    	
    		SELECT g.gname		FROM t_stu s INNER JOIN t_grades g 		ON s.sgid = g.gid		AND s.sname = #{name};		
   

在主文件mybatis.xml中加载两文件

然后封装对应的方法到StuGraDao类中

/** * 查询156班有哪些人 * @param name 班级名 * @return * @throws Exception */public List
   
     findAllByName(String name) throws Exception{	SqlSession sqlSession = null;	try {		sqlSession = MybatisUtil.getSqlSession();		return sqlSession.selectList(Student.class.getName() + ".findAllByName",name);			} catch (Exception e) {		e.printStackTrace();		throw e;	} finally {		MybatisUtil.closeSqlSession();	}}/** * 查询evan_qb是哪个班的 * @param name 学生姓名 * @return * @throws Exception */public Grade findByName(String name) throws Exception{	SqlSession sqlSession = null;	try {		sqlSession = MybatisUtil.getSqlSession();		return sqlSession.selectOne(Grade.class.getName() + ".findByName",name);	} catch (Exception e) {		e.printStackTrace();		throw e;	} finally {		MybatisUtil.closeSqlSession();	}}
   

多对多

以学生和课程为例

创建实体类Student和Course

Student类

package cn.qblank.many2many;import java.util.ArrayList;import java.util.List;public class Student {	private Integer id;	private String name;	private List
   
     courseList = new ArrayList<>();		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 List
    
      getCourseList() {		return courseList;	}	public void setCourseList(List
     
       courseList) {		this.courseList = courseList;	}}
     
    
   

Course类

package cn.qblank.many2many;import java.util.ArrayList;import java.util.List;public class Course {	private Integer id;	private String name;	private List
   
     stuList = new ArrayList<>();	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 List
    
      getStuList() {		return stuList;	}	public void setStuList(List
     
       stuList) {		this.stuList = stuList;	}}
     
    
   

创建对应的数据库表

-- 学生表CREATE TABLE t_stus(	sid INT PRIMARY KEY,	sname VARCHAR(20));-- 课程表CREATE TABLE t_courses(	cid INT PRIMARY KEY,	cname VARCHAR(20));-- 中间表CREATE TABLE middle(	msid INT,	mcid INT);

然后创建对应的映射文件StudentMapper.xml和CourseMapper.xml

StudentMapper.xml文件

   
   	
    		
     		
     	
    		
    	
    		SELECT s.sname		FROM t_stus s INNER JOIN middle m ON		s.sid = m.msid INNER JOIN t_courses c		ON m.mcid = c.cid		AND c.cname= #{name};	
   

CourseMapper.xml

   
   	
    		
     		
     	
    			
    	
    		SELECT c.cname		FROM t_stus s INNER JOIN middle m ON		s.sid = m.msid INNER JOIN t_courses c		ON m.mcid = c.cid		AND s.sname = #{name};	
   

在主文件mybatis.xml中加载文件

在CourseStuDao类中封装相应的方法

/** * 查询某人选学了哪些课程 * @param name 表示学生的姓名 */public List
   
     findAllByName(String name) throws Exception{	SqlSession sqlSession = null;	try{		sqlSession = MybatisUtil.getSqlSession();		return sqlSession.selectList(Course.class.getName() + ".findAllByName",name);	}catch(Exception e){		e.printStackTrace();		throw e;	}finally{		MybatisUtil.closeSqlSession();	}}/** * 查询某课程有哪些学生选修 * @param name 表示学生的课程 */public List
    
      findAllByCourseName(String name) throws Exception{	SqlSession sqlSession = null;	try{		sqlSession = MybatisUtil.getSqlSession();		return sqlSession.selectList(Student.class.getName() + ".findAllByCourseName",name);	}catch(Exception e){		e.printStackTrace();		throw e;	}finally{		MybatisUtil.closeSqlSession();	}}
    
   

就完成了mybatis的一对一，一对多，多对多的配置，通过配置我们可以发现，主要还是对sql语句的应用，所以学习mybatis还需对数据库的语句有一定的熟悉