Mybatis-Plus 实战完整学习笔记(六)------select测试一

查询方法（3.0.3）

1.查询一个员工的数据

 @Test
     public void selectMethod() throws SQLException {

         // 根据ID获取一个对象的数据
         Employee employee = employeeMapper.selectById(1);

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

     }

2.查询的字段设置

  @Test
     public void selectMethod() throws SQLException {

         // select 要查询的字段
         // SELECT email FROM tbl_employee
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().select("email"));

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

     }

相当于执行SELECT email FROM tbl_employee  这条sql语句

3.拼接where多条件和order by方法时候，不需要的可以直接去掉

 @Test
     public void selectMethod() throws SQLException {

         Employee employee = new Employee();

                 // where 条件查询和and添加和orderby使用
         // SELECT age FROM tbl_employee WHERE email = ? AND age = ? ORDER BY id ASC
         List<Employee> employeeList = employeeMapper.selectList(new QueryWrapper<Employee>().select("age").eq("email",employee.getEmail()).eq("age",employee.getAge()).orderBy(true,true,"id"));

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

     }

相当于SQL语句SELECT age FROM tbl_employee WHERE email = ? AND age = ? ORDER BY id ASC

4.批量查询

     @Test
     public void selectMethod() throws SQLException {

         List<Integer> idList = new  ArrayList<>();
         idList.add(1);
         idList.add(2);

         List<Employee> employeeList =employeeMapper.selectBatchIds(idList);

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

     }

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

5.Map查询封装

 @Test
     public void selectMethod() throws SQLException {

         Employee employee = employeeMapper.selectById(1);

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

         List<Employee> employeeList =employeeMapper.selectByMap(map);

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

     }

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

结果封装成map

 ++一个员工信息+++++[{"id":1,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":2,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":3,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":4,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":12,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":13,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":14,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":15,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":16,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":17,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":18,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":19,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":20,"lastName":"Marry","email":"1","gender":0,"age":55},{"id":21,"lastName":"Marry","email":"1","gender":0,"age":55}] (TestCRUD.java:146)