Mybatis-Plus 实战完整学习笔记(九)------条件构造器核心用法大全（上）

一、Mybatisplus通用（公共方法）CRUD，一共17种（3.0.3版），2.3系列也是这么多，这个新版本一定程度进行了改造和删减。

二、构造器UML图（3.0.3）-----实体包装器，主要用于处理 sql 拼接，排序，实体参数查询等

1. 注意: 使用的是数据库字段，不是 Java 属性!

总体就是入上图的样式的结构，主要使用QueryWrapper 和UpdateWrapper，JDK1.8使用LambdaQueryWrapper和LambdaUpdateWrapper

注意2.3版本使用的是EntityWrapper实现条件构造器，这里将阐述和说明

构造器拼接的方法

实战演练：(3.0.3版)

1、全部查询,拼接一个where过滤条件

 @Test
     public void selectWrapper() throws SQLException {

         // 条件构造器使用

         // 1、全部查询,拼接一个where过滤条件，如果是多个可以map中put多个，多个字段如果有某个字段是空的，就会默认添加空查询条件
         // SELECT id,last_name,email,gender,age FROM tbl_employee WHERE gender = ? AND age IS NULL
         Employee employee = new Employee();
         employee.setGender(1);

         Map<String,Object> map = new HashMap<>(16);
         map.put("gender",employee.getGender());
         map.put("age",employee.getAge());

        List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().allEq(map));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }
 }

注意2.3版本的可以用EntityWrapper代替QureyWrapper，其他写法一样

2、map添加的字段是否加到where的条件中

 @Test
     public void selectWrapper() throws SQLException {

         // 条件构造器使用
         Map<String,Object> map = new HashMap<>(16);
         map.put("gender",employee.getGender());
         map.put("age",employee.getAge());

         // 2、map添加的字段是否加到where的条件中，通过lambda表达式判断，如果是true就加入，反之，不加入，因为Map的key的String有gender，所以会过滤
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().allEq((String,Object)->String.equals("gender"),map));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }
 }

3、and使用

 @Test
     public void selectWrapper() throws SQLException {

         // 条件构造器使用
         // 3、and使用

         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().and(i -> i.eq("last_name", "Betty0")));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

相当于SQL语句SELECT id,last_name,email,gender,age FROM tbl_employee WHERE ( last_name = ? )

and前会有一个condition，判别是否加入到sql语句中的条件，默认是true
List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().and(true,i -> i.eq("last_name", "Betty0")));

4、apply拼接条件使用

     4、apply使用
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().apply("last_name='Betty0'"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

外部参数调用的话List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().apply("last_name={0}","Betty0"));

5、between使用方法

       5、between
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().between("age",20,50));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

6、eq 等于 =

    6、eq 充当and使用
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().eq("last_name","Betty0"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

7、ge大于等于 >=

     7、ge大于等于

         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().ge("age","40"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

8、gt大于

   // 8 、gt 大于
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().gt("age","40"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

9、分组操作

 //        9、分组操作
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().eq("id","25").groupBy("age","gender"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

10、having使用

   10、having使用
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().eq("gender","1").having("age = {0}",30));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

11、in使用

 //        11、in 操作
         List<Integer> idList = new ArrayList<>();
         idList.add(31);
         idList.add(32);

         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().in(true,"id",idList));
         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

12、inSql使用

    12、inSql使用
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().inSql("id", "12,22,23,24,25,26"));
         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

13、isNotNull字段值非空

   13、字段值非空
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().isNotNull("age"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

14、字段值为空的

  14、字段值为空的
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().isNull("age"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

15、结尾拼接sql语句，存在Sql注入风险，不建议使用

     15、结尾拼接sql语句
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().last("and age >30"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

16、小于等于 <=

  16、小于等于 <=
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().le("age", "20"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

17、小于

     17、小于
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().lt("age", "20"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

18、模糊查询

   18、模糊查询
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().like("age", "20"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

19、LikeLeft以什么结尾的查询

      19、 LikeLeft以什么结尾的查询
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().likeLeft("age", "20"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

20、likeRight以什么开头

   20、likeRight以什么开头
 //        List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().likeRight("age", "20"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

21、ne不等于 <>用法

    21、ne不等于 <>用法
          List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().ne("age", "20"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

22、嵌套的查询

 22、嵌套的查询
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().nested(true,i -> i.eq("last_name", "Betty0")));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

23、不在什么区间

 List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().notBetween("age",20,50));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

24、不存在notexist

   24、不存在
       List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().notExists("select id from tbl_employee where age = 1"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

25、存在exist

 25、存在
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().exists("select id from tbl_employee where age = 12"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

26、not in 不在区间内

 List<Integer> idList = new ArrayList<>();
         idList.add(31);
         idList.add(32);
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().notIn("id",idList));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

27、notSQL 不在区间内

  List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().notInSql("id","12,22"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

28、notLike 模糊查询没有这个关键字

 List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().notLike("age", "2"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

29、orderBy根据字段升序还是降序排序

 29、orderBy根据字段升序还是降序排序
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().orderBy(true, false, "age"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }

30、or或者

  30、or或者
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().eq("id","25").or().eq("gender","1"));

         if (!employeeList.isEmpty()) {
             logger.info("++条件构造器查询员工信息+++++" + gson.toJson(employeeList));
         }