mybatis之动态查询(超级详解)

一，引言

在学习一门新技术之前，还是需要下先看一下官网的
https://mybatis.org/mybatis-3/zh/dynamic-sql.html
在学spring的时候可能大家已经学了mybatis了，也许大家也学完了他的mybatis-plus，也或许在springboot整合mybatis中也写了大量的动态sql语句查询，但是今天还是总结了一下他的使用，以为这是成为java程序员的一门必修课。

用官网的一句话说就是 动态 SQL 是 MyBatis 的强大特性之一。如果你使用过 JDBC 或其它类似的框架，你应该能理解根据不同条件拼接 SQL 语句有多痛苦，例如拼接时要确保不能忘记添加必要的空格，还要注意去掉列表最后一个列名的逗号。利用动态 SQL，可以彻底摆脱这种痛苦。

二，数据库的建立

CREATE TABLE `users` (
  `user_key_id` bigint(20) NOT NULL AUTO_INCREMENT,
  `user_name` varchar(255) NOT NULL,
  `user_password` varchar(255) NOT NULL,
  `create_time` date NOT NULL,
  `update_time` date NOT NULL,
  PRIMARY KEY (`user_key_id`)
) ENGINE=InnoDB AUTO_INCREMENT=83 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

springboot项目的建立

pom.xml

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.12</version>
            <scope>provided</scope>
        </dependency>

application.properties

#端口号
server.port=8080
#清除缓存
spring.thymeleaf.cache=false
#配置mapper
mybatis.mapper-locations=classpath:mapper/*.xml
#开启驼峰映射
mybatis.configuration.map-underscore-to-camel-case=true 

application.yml

spring:
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mybatis-study?serverTimezone=GMT%2B8&useSSL=true
    username: root
    password: zhs03171812

model实体类

package com.zheng.model;


import java.util.Date;

public class User {
     
    private Integer userKeyId;
    private String userName;
    private String userPassword;
    private Date createTime;
    private Date updateTime;

    public Integer getUserKeyId() {
     
        return userKeyId;
    }

    public void setUserKeyId(Integer userKeyId) {
     
        this.userKeyId = userKeyId;
    }

    public String getUserName() {
     
        return userName;
    }

    public void setUserName(String userName) {
     
        this.userName = userName;
    }

    public String getUserPassword() {
     
        return userPassword;
    }

    public void setUserPassword(String userPassword) {
     
        this.userPassword = userPassword;
    }

    public Date getCreateTime() {
     
        return createTime;
    }

    public void setCreateTime(Date createTime) {
     
        this.createTime = createTime;
    }

    public Date getUpdateTime() {
     
        return updateTime;
    }

    public void setUpdateTime(Date updateTime) {
     
        this.updateTime = updateTime;
    }

    @Override
    public String toString() {
     
        return "User{" +
                "userKeyId=" + userKeyId +
                ", userName='" + userName + '\'' +
                ", userPassword='" + userPassword + '\'' +
                ", createTime=" + createTime +
                ", updateTime=" + updateTime +
                '}';
    }
}

三，测试

在controller中进行测试一下，看看代码能不能跑

package com.zheng.controller;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class controller {
     
    @RequestMapping("/h1")
    public String test(){
     
        return "hello world";
    }
}

建UserMapper

package com.zheng.mapper;

import com.zheng.model.User;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository
@Mapper
public interface UserMapper {
     
    //插入数据
    public int toInsert(User user);
    //获取全部的用户信息
    public List<User> getUsers();
    //删除数据
    public int toDelete(@Param("userName") String userName);
    //根据用户名进行用户的查询
    public User getUserById(@Param("userName") String id);
    //批量插入数据
    public int insertUsers(List<User> list);

    //动态sql之if
    public List<User> getUserByIf(User user);

    //动态sql之choose
    public List<User> getUserByChoose(User user);
}

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="com.zheng.mapper.UserMapper">
    <!--映射-->
    <!--建议加上，无论字段名是否一致-->
    <resultMap id="baseMap" type="com.zheng.model.User">
        <id column="user_key_id" property="userKeyId"></id>
        <result column="user_name" property="userName"></result>
        <result column="user_password" property="userPassword"></result>
        <result column="create_time" property="createTime"></result>
        <result column="update_time" property="updateTime"></result>
    </resultMap>

    <!--插入数据-->
    <insert id="toInsert" parameterType="com.zheng.model.User">
        insert into users (user_key_id,user_name,user_password,create_time,update_time)
        values (#{
     userKeyId},#{
     userName},#{
     userPassword},#{
     createTime},#{
     updateTime})
    </insert>

    <!--查询数据-->
    <select id="getUsers" resultMap="baseMap" resultType="java.util.List">
        select * from users;
    </select>

    <!--根据用户名删除用户-->
    <delete id="toDelete">
        delete from users where user_name = #{
     userName}
    </delete>

    <!--根据用户名查询用户信息-->
    <select id="getUserById" resultMap="baseMap" resultType="java.lang.String">
        select * from users where user_name = #{
     userName}
    </select>

    <!--批量插入用户信息-->
    <insert id="insertUsers" parameterType="java.util.List">
        insert into users (user_key_id,user_name,user_password,create_time,update_time)
        values
        <foreach collection="list" item="item" separator=",">
            (#{
     item.userKeyId},#{
     item.userName},#{
     item.userPassword},#{
     item.createTime},#{
     item.updateTime})
        </foreach>
    </insert>

    <!-- 动态sql之if -->
    <!-- 1=1 防止出现and重复的问题,后面加上and和or都行 -->
    <select id="getUserByIf" parameterType="com.zheng.model.User" resultType="java.util.List" resultMap="baseMap">
        select * from users where 1=1
        <if test="userKeyId != null and userKeyId !=''">
           and user_key_id = #{
     userKeyId}
        </if>
        <if test="userName != null and userName !=''">
            and user_name = #{
     userName}
        </if>
        <if test="userPassword != null and userPassword !=''">
            and user_password = #{
     userPassword}
        </if>
        <if test="createTime != null and createTime !=''">
            and create_Time = #{
     createTime}
        </if>
        <if test="updateTime != null and updateTime !=''">
            and update_time = #{
     updateTime}
        </if>
    </select>

    <!-- 动态choose -->
    <select id="getUserByChoose" parameterType="com.zheng.model.User" resultType="com.zheng.model.User" resultMap="baseMap">
        select * from users
        <where>
            <choose>
                <when test="userName == 'zhenghuisheng'">
                    user_name = #{
     userName}
                </when>
                <when test="userName == '538eaec3-a'">
                    user_name = #{
     userName}
                </when>
                <when test="userName == '94a1c998-d'">
                    user_name = #{
     userName}
                </when>
            </choose>
        </where>
    </select>

</mapper>

UserService.java

package com.zheng.service;

import com.zheng.model.User;
import org.apache.ibatis.annotations.Param;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public interface UserService {
     
    //插入数据
    public int toInsert(User user);
    //获取全部的用户信息
    public List<User> getUsers();
    //删除数据
    public int toDelete(@Param("userName") String userName);
    //根据用户名进行用户的查询
    public User getUserById(@Param("userName") String id);
    //批量插入数据
    public int insertUsers(List<User> list);
    //动态sql之if
    public List<User> getUserByIf(User user);
    //动态sql之choose
    public List<User> getUserByChoose(User user);
}

UserServiceImpl.java

package com.zheng.service.impl;

import com.zheng.mapper.UserMapper;
import com.zheng.model.User;
import com.zheng.service.UserService;
import org.apache.ibatis.annotations.Param;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;
import java.util.List;

/**
 * @author zhenghuisheng
 * @date 2021:17:05
 */

@Service
public class UserServiceImpl implements UserService {
     
    @Resource
    private UserMapper userMapper;

    //插入数据
    @Override
    public int toInsert(User user) {
     
        return userMapper.toInsert(user);
    }

    //查询全部数据
    @Override
    public List<User> getUsers() {
     
        return userMapper.getUsers();
    }

    //删除数据
    @Override
    public int toDelete(String userName) {
     
        return userMapper.toDelete(userName);
    }

    //根据用户名进行用户的查询
    public User getUserById(@Param("userName") String id){
     
        return userMapper.getUserById(id);
    }

    //批量插入数据
    @Override
    public int insertUsers(List<User> list) {
     
        return userMapper.insertUsers(list);
    }

    //动态sql查询
    @Override
    public List<User> getUserByIf(User user) {
     
        return userMapper.getUserByIf(user);
    }

    //动态sql之choose
    @Override
    public List<User> getUserByChoose(User user) {
     
        return userMapper.getUserByChoose(user);
    }

}

最终测试

package com.zheng;

import com.zheng.model.User;
import com.zheng.service.UserService;
import com.zheng.service.impl.UserServiceImpl;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

import javax.annotation.Resource;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.UUID;

/**
 * @author zhenghuisheng
 * @date 2021/03/07 18:37
 */

@SpringBootTest
class DemoApplicationTests {
     

    @Resource
    private UserServiceImpl userService;
    //插入数据的测试
    @Test
    void contextLoads() {
     
        User user = new User();
        //设置用户名为10为长度的id
        user.setUserName(UUID.randomUUID().toString().substring(0,10));
        //设置密码
        user.setUserPassword(UUID.randomUUID().toString().substring(0,6));
        user.setCreateTime(new Date());
        user.setUpdateTime(new Date());
        userService.toInsert(user);
        System.out.println("数据插入成功");
    }

    //查询数据的测试
    @Test
    public void test(){
     
        List<User> users = userService.getUsers();
        //将数据全部查询出
        users.forEach(e-> System.out.println(e));
    }

    //根据用户名进行id的删除
    @Test
    public void delete(){
     
        int i = userService.toDelete("d3ac4192-3");
        if (i > 0){
     
            System.out.println("数据删除成功");
        }
    }

    //根据username名进行用户的查询
    @Test
    public void getByID(){
     
        User zhenghuisheng = userService.getUserById("zhenghuisheng");
        if (!zhenghuisheng.equals("")){
     
            System.out.println("数据查询成功" + zhenghuisheng);
        }else{
     
            System.out.println("数据查询失败");
        }
    }

    @Test
    //批量插入20条数据
    public void insertUsers(){
     
        int count = 20;
        List<User> list = new ArrayList<>();
        for (int i = 0; i < count; i++) {
     
            User user = new User();
            //设置用户名为10为长度的id
            user.setUserName(UUID.randomUUID().toString().substring(0,10));
            //设置密码
            user.setUserPassword(UUID.randomUUID().toString().substring(0,6));
            user.setCreateTime(new Date());
            user.setUpdateTime(new Date());
            list.add(user);
        }
        userService.insertUsers(list);
    }

    @Test
    //动态sql查询语句之 if
    public void getUserByIf(){
     
        User user = new User();
        user.setUserName("48cae73e-d");
        user.setUserPassword("b60a54");
        List<User> userByIf = userService.getUserByIf(user);
        System.out.println("===================================");
        userByIf.forEach(e-> System.out.println(e));
        System.out.println("+++++++++++++++++++++++++++++++++++");
    }

    //动态sql查询语句之 choose
    @Test
    public void getUserByChoose(){
     
        User user = new User();
        user.setUserName("zhenghuisheng");
        List<User> userByChoose = userService.getUserByChoose(user);
        userByChoose.forEach(e-> System.out.println(e));
    }
}

总结

测试结果就先不粘贴出来了，可自行测试，都是没问题的代码。还有以上主要就是写了一些常用的动态sql语句，不常用的就先省略了！