mybatis之联表查询
今天碰到了一个问题，就是要在三张表里面各取一部分数据然后组成一个list传到前台页面显示。但是并不想在后台做太多判断，（因为涉及到for循环）会拉慢运行速度。正好用的框架是spring+springMVC+mybatis，所以很自然的就想到了联表查询。
一开始认为mybatis编写语句很简单，但是在编写的时候遇到了一些细节问题，所以发文记录一下。
先说一下背景：
框架：spring+springMVC+mybatis
表结构：
1、主表
2、从表
从表的uid对应主表的id，并将主表的id设为主键
接下来开始解析代码
先用mybatis的generator自动生成dao、mapper、model层
model层如下：
User.java
package am.model; import java.util.List; public class User { private Integer id; private String username; private String pwd; private List<Student> students; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username == null ? null : username.trim(); } public String getPwd() { return pwd; } public void setPwd(String pwd) { this.pwd = pwd == null ? null : pwd.trim(); } public List<Student> getStudents() { return students; } public void setStudents(List<Student> students) { this.students = students; } }
Student.java
package am.model; public class Student { private Integer id; private String position; private String level; private Integer uid; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getPosition() { return position; } public void setPosition(String position) { this.position = position == null ? null : position.trim(); } public String getLevel() { return level; } public void setLevel(String level) { this.level = level == null ? null : level.trim(); } public Integer getUid() { return uid; } public void setUid(Integer uid) { this.uid = uid; } }
需要注意的是在User表里面添加了成员变量
private List<Student> students;
这是因为联表查询时Student表为从表，你最终要将得到的数据放在主表User里
mapping层
UserMapper.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="am.dao.UserMapper" > <resultMap id="BaseResultMap" type="am.model.User" > <id column="id" property="id" jdbcType="INTEGER" /> <result column="username" property="username" jdbcType="VARCHAR" /> <result column="pwd" property="pwd" jdbcType="VARCHAR" /> </resultMap> <resultMap id="studentForListMap" type="am.model.User" > <id column="id" property="id" jdbcType="INTEGER" /> <result column="username" property="username" jdbcType="VARCHAR" /> <result column="pwd" property="pwd" jdbcType="VARCHAR" /> <collection property="students" javaType="java.util.List" ofType="am.model.Student"> <result column="id" property="id" jdbcType="INTEGER" /> <result column="position" property="position" jdbcType="VARCHAR" /> <result column="level" property="level" jdbcType="VARCHAR" /> </collection> </resultMap> <select id="studentForList" resultMap="studentForListMap" > select u.id,u.username,u.pwd,s.position,s.level from user u left join student s on u.id = s.uid </select> <sql id="Base_Column_List" > id, username, pwd </sql> <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" > select <include refid="Base_Column_List" /> from user where id = #{id,jdbcType=INTEGER} </select> <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" > delete from user where id = #{id,jdbcType=INTEGER} </delete> <insert id="insert" parameterType="am.model.User" > insert into user (id, username, pwd ) values (#{id,jdbcType=INTEGER}, #{username,jdbcType=VARCHAR}, #{pwd,jdbcType=VARCHAR} ) </insert> <insert id="insertSelective" parameterType="am.model.User" > insert into user <trim prefix="(" suffix=")" suffixOverrides="," > <if test="id != null" > id, </if> <if test="username != null" > username, </if> <if test="pwd != null" > pwd, </if> </trim> <trim prefix="values (" suffix=")" suffixOverrides="," > <if test="id != null" > #{id,jdbcType=INTEGER}, </if> <if test="username != null" > #{username,jdbcType=VARCHAR}, </if> <if test="pwd != null" > #{pwd,jdbcType=VARCHAR}, </if> </trim> </insert> <update id="updateByPrimaryKeySelective" parameterType="am.model.User" > update user <set > <if test="username != null" > username = #{username,jdbcType=VARCHAR}, </if> <if test="pwd != null" > pwd = #{pwd,jdbcType=VARCHAR}, </if> </set> where id = #{id,jdbcType=INTEGER} </update> <update id="updateByPrimaryKey" parameterType="am.model.User" > update user set username = #{username,jdbcType=VARCHAR}, pwd = #{pwd,jdbcType=VARCHAR} where id = #{id,jdbcType=INTEGER} </update> </mapper>
需要注意
1、property="students"中的students必须与User.java中的private List<Student> students;中的students命名一样
2、resultMap="studentForListMap"必须与<resultMap id="studentForListMap" type="am.model.User" >中的id一致
<resultMap id="studentForListMap" type="am.model.User" > <id column="id" property="id" jdbcType="INTEGER" /> <result column="username" property="username" jdbcType="VARCHAR" /> <result column="pwd" property="pwd" jdbcType="VARCHAR" /> <collection property="students" javaType="java.util.List" ofType="am.model.Student"> <result column="id" property="id" jdbcType="INTEGER" /> <result column="position" property="position" jdbcType="VARCHAR" /> <result column="level" property="level" jdbcType="VARCHAR" /> </collection> </resultMap> <select id="studentForList" resultMap="studentForListMap" > select u.id,u.username,u.pwd,s.position,s.level from user u left join student s on u.id = s.uid </select>
dao层
UserMapper.java
package am.dao; import java.util.List; import am.model.User; public interface UserMapper { int deleteByPrimaryKey(Integer id); int insert(User record); int insertSelective(User record); User selectByPrimaryKey(Integer id); int updateByPrimaryKeySelective(User record); int updateByPrimaryKey(User record); List<User> queryForList(); List<User> studentForList(); }
spring-mybatis.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd"> <!-- 自动扫描 --> <context:component-scan base-package="am.*" /> <!-- 引入配置文件 --> <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="location" value="classpath:jdbc.properties" /> </bean> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="${driver}" /> <property name="url" value="${url}" /> <property name="username" value="${username}" /> <property name="password" value="${password}" /> <!-- 初始化连接大小 --> <property name="initialSize" value="${initialSize}"></property> <!-- 连接池最大数量 --> <property name="maxActive" value="${maxActive}"></property> <!-- 连接池最大空闲 --> <property name="maxIdle" value="${maxIdle}"></property> <!-- 连接池最小空闲 --> <property name="minIdle" value="${minIdle}"></property> <!-- 获取连接最大等待时间 --> <property name="maxWait" value="${maxWait}"></property> </bean> <!-- spring和MyBatis完美整合，不需要mybatis的配置映射文件 --> <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="dataSource" /> <!-- 自动扫描mapping.xml文件 --> <property name="mapperLocations" value="classpath:am/mapping/*.xml"></property> </bean> <!-- DAO接口所在包名，Spring会自动查找其下的类 --> <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"> <property name="basePackage" value="am.dao" /> <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property> </bean> <!-- (事务管理)transaction manager, use JtaTransactionManager for global tx --> <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <property name="dataSource" ref="dataSource" /> </bean> </beans>
我用serviceImp层来继承service层实现dao层，当然你也可以直接实现dao层，在这里就不多做赘述了。
分享一下项目包结构：
最后做一点简单的测试
MybatisController
package am.controller; import java.util.List; import javax.annotation.Resource; import javax.servlet.http.HttpServletRequest; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.servlet.ModelAndView; import com.alibaba.fastjson.JSON; import am.model.User; import am.service.UserService; @Controller @RequestMapping("/my") public class MybatisController { @Resource private UserService userService; @RequestMapping("/t") public ModelAndView test(HttpServletRequest request){ ModelAndView view = new ModelAndView("test"); List<User> users = userService.studentForList(); String s = JSON.toJSONString(users); System.out.println(JSON.toJSONString(users)); return view; } }
success，得到想要数据。
