Mybatis-Plus 实战完整学习笔记(七)------select测试二

1.查询selectOne  （3.0.3版）

 @Test
     public void selectMethod() throws SQLException {

      // 根据ID获取一个对象的数据

         Employee employee =employeeMapper.selectOne(new QueryWrapper<Employee>().eq("id","1"));

         if (employee!=null) {
             logger.info("++一个员工信息+++++"+gson.toJson(employee));
         }

     }

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

2.3版本的写法是直接注入一个对象，对象的set值就是查询的条件,同时，ID要是Long或Integer类型，条件一定要唯一，否则，会报数据重复的异常。

 Employee employee = new Employee()；
         employee.setId(1);

         Employee result =employeeMapper.selectOne(employee);

         if (result!=null) {
             logger.info("++一个员工信息+++++"+gson.toJson(result));
         }

2、查询selectMaps（3.0.3新出）

 @Test
     public void selectMethod() throws SQLException {

         // 6、多个Map查询
         Employee employee = employeeMapper.selectById(1);

         QueryWrapper<Employee> employeeQueryWrapper = new QueryWrapper<>();

         List<Map<String, Object>> employeeList =employeeMapper.selectMaps(employeeQueryWrapper);

         if (!employeeList.isEmpty()) {
             logger.info("++一个员工信息+++++"+gson.toJson(employeeList));
         }

     }

写法跟其他的查询没有区别，只是返回的结果，变成List<Map<String,Object>>，条件查询跟上边的一样。

返回样式

 ++一个员工信息+++++[{"gender":"0","last_name":"Marry","id":1,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":2,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":3,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":4,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":12,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":13,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":14,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":15,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":16,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":17,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":18,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":19,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":20,"email":"1","age":55},{"gender":"0","last_name":"Marry","id":21,"email":"1","age":55}] (TestCRUD.java:159) 

本来以为是要装多个map进去查询就写成下边的样子，结果不是那个意思

  // 6、多个Map查询
         Employee employee = employeeMapper.selectById(1);

         Map<String,Object> map1 = new HashMap<>(16);
         map1.put("email",employee.getEmail());
         map1.put("age",employee.getAge());

         Employee employee2 = employeeMapper.selectById(2);
         Map<String,Object> map2 = new HashMap<>(16);
         map2.put("email",employee2.getEmail());
         map2.put("age",employee2.getAge());

         List<Map<String,Object>> mapList = new ArrayList<>();
         mapList.add(map1);
         mapList.add(map2);

         QueryWrapper<List<Map<String, Object>>> maps = new QueryWrapper<List<Map<String, Object>>>();
         maps.setEntity((mapList));

         List<Map<String, Object>> employeeList =employeeMapper.selectMaps(maps);

3、查询selectObjs

 @Test
     public void selectMethod() throws SQLException {

         // 7、selectObjs
         Employee employee = employeeMapper.selectById(1);

         List<Object> employeeList =employeeMapper.selectObjs(new QueryWrapper<Employee>().eq("email",employee.getEmail()));

         if (!employeeList.isEmpty()) {
             logger.info("++一个员工信息+++++"+gson.toJson(employeeList));
         }

     }

用法一样，就是返回的结果是个Object类型。

4、统计结果查询selectCount

  @Test
     public void selectMethod() throws SQLException {

         // 8、selectCount
          Employee employee = employeeMapper.selectById(1);

         Integer count = employeeMapper.selectCount(new QueryWrapper<Employee>().eq("email", employee.getEmail()));

         if (count > 0) {
             logger.info("++统计结果：+++++" + count);
         }

     }

5、分页查询selectPage

 @Test
     public void selectMethod() throws SQLException {

 //        9、分页查询

         Integer count = employeeMapper.selectCount(new QueryWrapper<Employee>().between("age", 0, 100)
                 .eq("gender", 0));

         IPage<Employee> employeeIPage = new Page<Employee>(1, 3,count);

         IPage<Employee>  employeeList = employeeMapper.selectPage(employeeIPage,new QueryWrapper<Employee>()
                 .between("age", 0, 100)
                 .eq("gender", 0));

         if (!employeeList.getRecords().isEmpty()) {
             logger.info("++一个员工信息+++++" + gson.toJson(employeeList));
         }

 }

6、分页查询返回map类型的selectMapsPage

 @Test
     public void selectMethod() throws SQLException {

         // 10、分页查询Map结果返回
         Integer count = employeeMapper.selectCount(new QueryWrapper<Employee>().between("age", 0, 100)
                 .eq("gender", 0));

         IPage<Employee> employeeIPage = new Page<Employee>(1, 3, count);

         IPage<Map<String, Object>> employeeList = employeeMapper.selectMapsPage(employeeIPage, new QueryWrapper<Employee>()
                 .between("age", 0, 100)
                 .eq("gender", 0));

         if (!employeeList.getRecords().isEmpty()) {
             logger.info("++一个员工信息+++++" + gson.toJson(employeeList));
         }

     }

System.out.println("返回数据："+employeeIPage.getRecords());

System.out.println("总条数："+page.getTotal());

System.out.println("当前页码："+page.getCurrent());

System.out.println("总页码："+page.getPages());

System.out.println("每页显示条数："+page.getSize());

System.out.println("是否有上一页："+page.hasPrevious());

System.out.println("是否有下一页："+page.hasNext());

System.out.println("返回的数据："+page.getRecords());