利用反射生成 MyBatisPlus中QueryWrapper动态条件

╰半夏微凉° 2022-09-04 03:49 232阅读 0赞

## 问题 ##

在MyBatisPlus中经常会用到如下所示的代码来构造查询条件：

QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    
    if (userQuery.getId() != null) { 
        queryWrapper.eq("id", userQuery.getId());
    }
    if (userQuery.getName() != null) { 
        queryWrapper.like("name", userQuery.getName());
    }
    if (userQuery.getNickname() != null) { 
        queryWrapper.like("nickname", userQuery.getNickname());
    }
    if (userQuery.getAccount() != null) { 
        queryWrapper.eq("account", userQuery.getAccount());
    }
    if (userQuery.getGender() != null) { 
        queryWrapper.eq("gender", userQuery.getGender());
    }
    if (userQuery.getBirth1() != null) { 
        queryWrapper.ge("birth", userQuery.getBirth1());
    }
    if (userQuery.getBirth2() != null) { 
        queryWrapper.le("birth", userQuery.getBirth2());
    }
    if (userQuery.getTel() != null) { 
        queryWrapper.eq("tel", userQuery.getTel());
    }
    if (userQuery.getEmail() != null) { 
        queryWrapper.eq("email", userQuery.getEmail());
    }
    if (userQuery.getQq() != null) { 
        queryWrapper.eq("qq", userQuery.getQq());
    }
    if (userQuery.getWechat() != null) { 
        queryWrapper.eq("wechat", userQuery.getWechat());
    }
    if (userQuery.getHomePage() != null) { 
        queryWrapper.eq("home_page", userQuery.getHomePage());
    }
    //.........
    baseMapper.selectPage(page, queryWrapper);

大量这样的代码，可以通过如下所示的反射技术生成，从而一劳永安逸：

## 优化方案 ##

public class APP{ 
    
        public static void main(String[] args) throws Exception { 
            QueryWrapper<Dept> queryWrapper = new QueryWrapper<>();
            Dept dept = Dept.builder()
                    .deptno(1234)
    // .dname("sales")
                    .loc("NEWYORK")
                    .build();
    
            Method[] methods = Dept.class.getDeclaredMethods();
            for (Method method : methods) { 
                String methodName = method.getName();
                if (methodName.contains("get")) { 
                    Object res = method.invoke(dept, null);
                    if(res != null){ 
                        String columnName = getColumnName(methodName);
                        queryWrapper.eq(columnName,res);
                    }
                }
            }
    
            System.out.println(queryWrapper);//在此处设置断点，可以查看保存到QueryWrapper中的值
        }
    
        // 根据getter方法名得到对应表的字段名
        public static String getColumnName(String name) { 
            StringBuffer sb = new StringBuffer();
            name = name.substring(3, name.length()); //去掉get前缀
            char[] chars = name.toCharArray();
            for (int i = 0; i < chars.length; i++) { 
                char item = chars[i];
                if (item > 65 && item < 90) { //大写字母
                    sb.append("_");
                    sb.append((char)(item+32));
                }else { 
                    sb.append(item);
                }
            }
            return sb.deleteCharAt(0).toString();
        }
    }