Dynamic SQL - Mybatis

Posted 2023-03-30 Erato Rabbit

1 Static SQL/Ordinary Multi Conditons Query

1/ Declare method in interface EmpMapper

//Query according to id, lastName, age, sex. Query Employee by Multiple conditions
public List<Emp> getEmpListByMultiConditions(Emp emp);

2/ Configure SQL Statement in EmpMapper.xml

2 Tag If

1/ Declare method in interface EmpMapper

public List<Employee> getEmpsByConditionsIf(Employee employee);

2/ Configure SQL statement in EmpMapper.xml

    <select id="getByConditionIf" resultType="Employee">
        select * from tbl_employee
        where id = -1
        
            <if test="lastName!=null and lastName!=''">
                and last_name like #lastName
            </if>
            <if test="email!=null and email.trim()!=&quot;&quot;">
                and email = #email
            </if>
            <if test="gender==0 or gender==1">
                and gender = #gender
            </if>
    
    </select>

<test> is OGNL(Object-Graph Navigation Language) statement
OGNL - Apache Commons OGNL - Object Graph Navigation Library

If you meet special character, escape it.

" : "
& : &

@Test
public void testSelectIf() 

	Employee emp = new Employee();
	emp.setLastName("Zhang");
	List<Emp> emps = empDao.getByConditionIf(emp);
	
	emps.forEach(emp -> sout(stu + ","));

根据上面三个代码块，将其中的内容转为等价的 sql 语句如下：👇👇👇

select *
from student
where id=-1 or name="张起灵" or age=20

Tag where

使用标签，在有 query condition 时，mybatis 会自动添加上 where 子句；没有 query condition 时，不会添加 where 子句.

需要注意的是，第一个标签中的SQL 片断，and 写不写都行。如果写上了 and ，tag where 会将离它最近的 and 或者 or 删掉。

但其它中 SQL 片断的 and，必须写上。否则 SQL 语句将拼接出错。

Reference

MyBatis（五）动态SQL 之 if 与 where 标签 - 格物致知_Tony - 博客园 (cnblogs.com)

IDEA+SpringBoot MyBatis Dynamic SQL的初体验（二)

在上节IDEA+SpringBoot MyBatis Dynamic SQL的初体验（一)中，讲解了Mybatis Dynamic SQL数据库生成https://www.cnblogs.com/hjm0928/p/9955228.html

现在那看一下怎么使用

先看一下项目结构

可以看到实体类，Mapper文件和DynamicSqlSupport文件都生成成功了

第一步 修改application.properties修改为application.yml  内容如下

spring:
    datasource:
        driver-class-name: com.mysql.cj.jdbc.Driver
        url: jdbc:mysql://localhost:3306/nice_test?useUnicode=true&useSSL=false&characterEncoding=utf8&serverTimezone=UTC
        username: pigge
        password: 123456
    http:
        encoding:
            force: true
mybatis:
    mapper-locations: com.pigge.mybatistest.mapper
server:
    tomcat:
        uri-encoding: UTF-8
    port: 8080
logging:
    level:
        # 打开日志输出
        com.pigge.mybatistest: DEBUG
    path: logs\\spring
debug: true

在创建UserService类

package com.pigge.mybatistest.service;

import com.pigge.mybatistest.entity.User;
import com.pigge.mybatistest.util.Page;
import org.apache.ibatis.annotations.Param;

import java.util.List;

/**
 * @author hjm0928
 */
public interface UserService {
    /**
     * 根据用户名查询表内数据
     * @param username 用户名
     * @return 数据列表
     */
    User selectByUsername(@Param("username")String username);

    /**
     * 分页查找数据
     * @param page 分页工具类
     * @return 记录集
     */
    List<User> selectAll(Page page);
}

UserServiceImpl类

package com.pigge.mybatistest.service.impl;

import com.pigge.mybatistest.entity.User;
import com.pigge.mybatistest.mapper.UserDynamicSqlSupport;
import com.pigge.mybatistest.mapper.UserMapper;
import com.pigge.mybatistest.service.UserService;
import com.pigge.mybatistest.util.Page;
import com.sun.org.apache.bcel.internal.generic.InstructionComparator;
import com.sun.org.apache.bcel.internal.generic.Select;
import org.mybatis.dynamic.sql.render.RenderingStrategy;
import org.mybatis.dynamic.sql.where.condition.IsEqualTo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

import static org.mybatis.dynamic.sql.select.SelectDSL.select;


/**
 * @author hjm0928
 */
@Service
public class UserServiceImpl implements UserService {

    private final UserMapper userMapper;

    @Autowired
    public UserServiceImpl(UserMapper userMapper) {
        this.userMapper = userMapper;
    }

    @Override
    public User selectByUsername(String username) {
        InstructionComparator select = Select.getComparator();
        //SQL语句为 select username, password, tel from user where username = ?; 参数username
        User user = userMapper.selectOne(
                select(
                        UserDynamicSqlSupport.username,
                        UserDynamicSqlSupport.password,
                        UserDynamicSqlSupport.tel
                ).from(UserDynamicSqlSupport.user)
                .where(UserDynamicSqlSupport.username, IsEqualTo.of(()->username))
                .build()
                .render(RenderingStrategy.MYBATIS3)
        );
        //SQL语句 select username....(所有字段) from user where username = ?; 参数username
        user = userMapper.selectByExample()
                .where(UserDynamicSqlSupport.username, IsEqualTo.of(()->username))
                .build()
                .execute()
                .get(0);
        return user;
    }

    @Override
    public List<User> selectAll(Page page) {
        //下一节实现 因为Mybatis Dynamic Sql没有默认的分页支持， 只能自定义
        return null;
    }
}

UserController类

package com.pigge.mybatistest.controller;

import com.fasterxml.jackson.databind.util.JSONPObject;
import com.pigge.mybatistest.entity.User;
import com.pigge.mybatistest.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

/**
 * @author hjm0928
 */
@Controller
public class UserController {

    private final UserService userService;

    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

    @RequestMapping("/get")
    @ResponseBody
    private User get(String username){
        return userService.selectByUsername(username);
    }
}

此时项目结构为

运行MyBatisTestApplication类， 在浏览器中输入http://localhost:8080/get?username=youUsername 其页面结果为

后台日志输出为

ok  测试成功