mybatis学习之高级映射

一对一映射查询

1、数据库执行脚本：

/*
SQLyog Ultimate v12.09 (64 bit)
MySQL - 5.7.11-log : Database - db_mybatis
*********************************************************************
*/


/*!40101 SET NAMES utf8 */;

/*!40101 SET SQL_MODE=''*/;

/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
CREATE DATABASE /*!32312 IF NOT EXISTS*/`db_mybatis` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci */;

USE `db_mybatis`;

/*Table structure for table `t_address` */

DROP TABLE IF EXISTS `t_address`;

CREATE TABLE `t_address` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `pro` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `city` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `country` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

/*Data for the table `t_address` */

insert  into `t_address`(`id`,`pro`,`city`,`country`) values (1,'江苏省','苏州市','姑苏区'),(2,'江苏省','南京市','鼓楼区');

/*Table structure for table `t_student` */

DROP TABLE IF EXISTS `t_student`;

CREATE TABLE `t_student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `addressId` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `addressId` (`addressId`)
) ENGINE=InnoDB AUTO_INCREMENT=33 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

/*Data for the table `t_student` */

insert  into `t_student`(`id`,`name`,`age`,`addressId`) values (32,'张三那',23,1);

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

这里使用2张表，学生表t_student、地址表t_address，演示查询学生时查询出对应的地址对象，首先是StudentDao：

package com.cz.mappers;

import java.util.List;

import com.cz.model.Student;

public interface StudentDao {
    /**
     * 新增
     * @param student
     * @return
     */
    public int add(Student student);
    /**
     * 修改
     * @param student
     * @return
     */
    public int update(Student student);
    /**
     * 删除
     * @param student
     * @return
     */
    public int delete(Integer id); 
    /**
     * 根据id查找 
     * @param id
     * @return
     */
    public Student findById(Integer id);
    /**
     * 查找 
     * @param id
     * @return
     */
    public List<Student> find();
    
    /**
     * 根据学生id查询带地址的学生信息
     * @param id
     * @return
     */
    public Student findWithAddr(Integer id);
}

Student实体类：

package com.cz.model;

public class Student {
    
    private Integer id;
    private String name;
    private int age;

    private Address address;
    
    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    
    public Student(Integer id, String name, int age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }
    
    public Student() {
        super();
    }
    
    public Address getAddress() {
        return address;
    }
    
    public void setAddress(Address address) {
        this.address = address;
    }

    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 int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age + ", address=" + address + "]";
    }
    
    
}

Address实体类：

package com.cz.model;

public class Address {
    
    private Integer id;
    private String pro;
    private String city;
    private String country;
    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getPro() {
        return pro;
    }
    public void setPro(String pro) {
        this.pro = pro;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public String getCountry() {
        return country;
    }
    public void setCountry(String country) {
        this.country = country;
    }
    @Override
    public String toString() {
        return "Address [id=" + id + ", pro=" + pro + ", city=" + city + ", country=" + country + "]";
    }
    
    
    
}

AddressDao：

package com.cz.mappers;

import com.cz.model.Address;

public interface AddressDao {
    /**
     * 根据id查找
     * @param id
     * @return
     */
    public Address findById(Integer id);
    
}

StudentMapper.xml映射文件：

1）、直接result属性映射

<resultMap type="Student" id="StudentResult">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        <result property="address.id" column="addressId"/>
        <result property="address.pro" column="pro"/>
        <result property="address.city" column="city"/>
        <result property="address.country" column="country"/>
    </resultMap>
    
    <select id="findWithAddr" parameterType="Integer" resultMap="StudentResult">
        select * from t_student t1,t_address t2 where t1.addressId = t2.id and t1.id = #{id}
    </select>

这里直接配置对应property属性，column为数据库对应的字段名称，property为javabean对应的字段，这里使用address.id，mybatis会自动为我们进行封装，封装到Student实体的Address属性上。

junit测试如下：

package com.cz.test;


import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.cz.mappers.StudentDao;
import com.cz.model.Student;
import com.cz.utill.SqlSessionFactoryUtil;

public class StudentTest2 {
    
    public static Logger logger = Logger.getLogger(StudentTest2.class);
    SqlSession sqlSession = null;
    StudentDao studentDao = null; // 返回student dao接口

    @Before
    public void setUp() throws Exception {
        sqlSession = SqlSessionFactoryUtil.openSession();
        studentDao = sqlSession.getMapper(StudentDao.class);
        logger.info("开始执行了");
    }
    
    @After
    public void tearDown() throws Exception {
        sqlSession.close();
        logger.info("执行结束了");
    }
    
    /**
     * 学生查询，带地址查询
     * @throws Exception
     */
    @Test
    public void testFindWithAddr() throws Exception {
        Student student = studentDao.findWithAddr(32);
        sqlSession.commit();
        System.out.println(student);
    }
}

2）、Association和ResultMap形式：

<resultMap type="Student" id="StudentResult">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        
        <association property="address" resultMap="AddressResult"/>
        
    </resultMap>
    
    <resultMap type="Address" id="AddressResult">
        <result property="id" column="id"/>
        <result property="pro" column="pro"/>
        <result property="city" column="city"/>
        <result property="country" column="country"/>
    </resultMap>

3）、第二种方式映射时，Address的resultMap嵌套在Student的映射文件中，不利于代码的复用，改进版：

<resultMap type="Student" id="StudentResult">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        
        <association property="address" column="addressId" select="com.cz.mappers.AddressDao.findById"></association>
    </resultMap>

这里使用association进行关联映射，column为Student实体对应的表中关联address的字段名称，select表示该字段值通过其它映射语句直接查询返回，传的id参数即这里的addressId，AddressMapper.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.cz.mappers.AddressDao">
    
    <resultMap type="Address" id="AddressResult">
        <result property="id" column="id"/>
        <result property="pro" column="pro"/>
        <result property="city" column="city"/>
        <result property="country" column="country"/>
    </resultMap>
    <select id="findById" resultType="Address" parameterType="Integer"> select * from t_address where id=#{id} </select>
</mapper>

一对多映射查询

1、数据导入：

/*
Navicat MySQL Data Transfer

Source Server         : 192.168.20.132
Source Server Version : 50711
Source Host           : localhost:3306
Source Database       : db_mybatis

Target Server Type    : MYSQL
Target Server Version : 50711
File Encoding         : 65001

Date: 2016-07-01 17:53:44
*/

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for t_grade
-- ----------------------------
DROP TABLE IF EXISTS `t_grade`;
CREATE TABLE `t_grade` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `gradeName` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

-- ----------------------------
-- Records of t_grade
-- ----------------------------
INSERT INTO `t_grade` VALUES ('1', '一年级');
INSERT INTO `t_grade` VALUES ('2', '二年级');

新建年级表t_grade，年级对学生为一对多关系。

首先是根据年级查询该年级下的所有学生：

1）、新建Grade实体类：

package com.cz.model;
import java.util.List;

/**
 * 年级类
 * @author Administrator
 *
 */
public class Grade {
    
    private Integer id;
    private String gradeName;
    
    private List<Student> students;
    
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }
    
    public String getGradeName() {
        return gradeName;
    }
    
    public void setGradeName(String gradeName) {
        this.gradeName = gradeName;
    }
    
    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }
    
    @Override
    public String toString() {
        return "Grade [id=" + id + ", gradeName=" + gradeName  + "]";
    }
    
}

通过students实例属性关联，然后是GradeDao接口实现：

package com.cz.mappers;

import com.cz.model.Grade;

public interface GradeDao {
    /**
     * 根据id查找（完整字段）
     * @param id
     * @return
     */
    public Grade findById(Integer id);
}

只有一个方法findById，这里查询时会顺带查出该年级下的所有学生信息，GradeMapper映射文件如下：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.cz.mappers.GradeDao">

    <resultMap type="Grade" id="GradeResult">
        <result property="id" column="id" />
        <result property="gradeName" column="gradeName" />
        
        <!-- 映射students集合 -->
        <collection property="students" column="id" select="com.cz.mappers.StudentDao.findByGradeId"></collection>
    </resultMap>
    
    <select id="findById" parameterType="Integer" resultMap="GradeResult">
        select * from t_grade where id = #{id}
    </select>
</mapper>

mybatis多对一关联使用collection标签实现，column为Grade实体对应的表的字段，select表示使用该字段进行关联查询，StudentDao的findByGradeId具体实现如下：

首先是Dao层：

package com.cz.mappers;

import java.util.List;

import com.cz.model.Student;

public interface StudentDao {
    /**
     * 新增
     * @param student
     * @return
     */
    public int add(Student student);
    /**
     * 修改
     * @param student
     * @return
     */
    public int update(Student student);
    /**
     * 删除
     * @param student
     * @return
     */
    public int delete(Integer id); 
    /**
     * 根据id查找 
     * @param id
     * @return
     */
    public Student findById(Integer id);
    /**
     * 查找 
     * @param id
     * @return
     */
    public List<Student> find();
    
    /**
     * 根据学生id查询带地址的学生信息
     * @param id
     * @return
     */
    public Student findWithAddr(Integer id);
    /**
     * 根据gradeId查询Student对象
     * @param id
     * @return
     */
    public List<Student> findByGradeId(Integer gradeId);
}

然后是映射文件：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.cz.mappers.GradeDao">

    <resultMap type="Grade" id="GradeResult">
        <result property="id" column="id" />
        <result property="gradeName" column="gradeName" />
        
        <!-- 映射students集合 -->
        <collection property="students" column="id" select="com.cz.mappers.StudentDao.findByGradeId"></collection>
    </resultMap>
    
    <select id="findById" parameterType="Integer" resultMap="GradeResult">
        select * from t_grade where id = #{id}
    </select>
</mapper>

然后是StudentDao对应的映射文件StudentMapper：

<resultMap type="Student" id="StudentResult">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        
        <!-- 一对一关联 -->
        <association property="address" column="addressId" select="com.cz.mappers.AddressDao.findById"></association>    
        <association property="grade" column="gradeId" select="com.cz.mappers.GradeDao.findById"></association>
    </resultMap>
    
    <select id="findByGradeId" parameterType="Integer" resultMap="StudentResult">
        select * from t_student where gradeId = #{gradeId}
    </select>

这里Student配置了一个grade属性，目的是后边查询学生顺带查询出其所属的班级信息，Student实体具体实现：

package com.cz.model;

public class Student {
    
    private Integer id;
    private String name;
    private int age;

    private Address address;
    
    private Grade grade;
    
    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    
    public Student(Integer id, String name, int age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }
    
    public Student() {
        super();
    }
    
    public Address getAddress() {
        return address;
    }
    
    public void setAddress(Address address) {
        this.address = address;
    }

    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 int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }

    public Grade getGrade() {
        return grade;
    }

    public void setGrade(Grade grade) {
        this.grade = grade;
    }
    
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age + ", address=" + address + ", grade=" + grade
                + "]";
    }
    
}

junit测试部分（根据学生查询对应年级信息）：

/**
     * 学生查询，带地址查询
     * @throws Exception
     */
    @Test
    public void testFindWithAddr() throws Exception {
        Student student = studentDao.findWithAddr(32);
        sqlSession.commit();
        System.out.println(student);
    }

junit测试部分（根据年级信息查询对应学生信息）：

package com.cz.test;


import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import com.cz.mappers.GradeDao;
import com.cz.model.Grade;
import com.cz.utill.SqlSessionFactoryUtil;

public class GradeTest {
    
    public static Logger logger = Logger.getLogger(GradeTest.class);
    SqlSession sqlSession = null;
    GradeDao gradeDao = null; // 返回student dao接口

    @Before
    public void setUp() throws Exception {
        sqlSession = SqlSessionFactoryUtil.openSession();
        gradeDao = sqlSession.getMapper(GradeDao.class);
        logger.info("开始执行了");
    }
    
    @After
    public void tearDown() throws Exception {
        sqlSession.close();
        logger.info("执行结束了");
        
    }
    
    /**
     * 年级查询（加年级下所有学生信息）
     * @throws Exception
     */
    @Test
    public void testFindGradeWithStudents() throws Exception {
        Grade grade = gradeDao.findById(1);
        System.out.println(grade);
    }
}