问题描述

在MyBatisPlus中经常会用到构造复杂查询条件的情况，比如：

• 测试代码

@SpringBootTest
class Query2WrapperTest {
    @Resource
    private UserMapper userMapper;

    @Test
    void fun() {
        UserQuery userQuery = UserQuery.builder()
                .state(1)
                .gender(0)
                .info("中")
                .build();

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        qeury2Wrapper(userQuery, queryWrapper);


        List<User> list = userMapper.selectList(queryWrapper);
        list.forEach(System.out::println);
    }

• 构造查询条件

    private void qeury2Wrapper(UserQuery userQuery, QueryWrapper<User> queryWrapper) {
        if (userQuery == null || queryWrapper == null) {
            return;
        }
        //将UserQuery的值赋到queryWrapper中
        if (userQuery.getId() != null) {
            queryWrapper.eq("id", userQuery.getId());
        }
        if (userQuery.getNickname() != null) {
            queryWrapper.like("nickname", userQuery.getNickname());
        }
        if (userQuery.getGender() != null) {
            queryWrapper.eq("gender", userQuery.getGender());
        }

        if (userQuery.getBirthMin() != null) {
            queryWrapper.ge("birth", userQuery.getBirthMin());
        }
        if (userQuery.getBirthMax() != null) {
            queryWrapper.le("birth", userQuery.getBirthMax());
        }
        if (userQuery.getEmail() != null) {
            queryWrapper.eq("email", userQuery.getEmail());
        }

        if (userQuery.getTel() != null) {
            queryWrapper.eq("tel", userQuery.getTel());
        }
        if (userQuery.getAccount() != null) {
            queryWrapper.eq("account", userQuery.getAccount());
        }
        if (userQuery.getInfo() != null) {
            queryWrapper.like("info", userQuery.getInfo());
        }
        if (userQuery.getState() != null) {
            queryWrapper.eq("state", userQuery.getState());
        }
    }

像上面这种手写转换不仅繁琐，而且容易出错，其实采用借助反射或内省的方式提取公共类，简化代码的书写。

反射方式

    private void qeury2Wrapper2(UserQuery userQuery, QueryWrapper<User> queryWrapper) throws Exception {
        Method[] methods = userQuery.getClass().getDeclaredMethods();
        for (Method method : methods) {
            String methodName = method.getName();
            if (methodName.contains("get")) {
                Object res = method.invoke(userQuery, null);
                if (res != null) {
                    String columnName = getColumnName(methodName);
                    queryWrapper.like(columnName, res);
                }
            }
        }
    }

内省方式

 private void qeury2Wrapper3(UserQuery userQuery, QueryWrapper<User> queryWrapper) throws Exception {
        BeanInfo beanInfo = Introspector.getBeanInfo(userQuery.getClass());
        PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
        for (PropertyDescriptor pd : pds) {
            Method readMethod = pd.getReadMethod();
            if (readMethod.getName().equals("getClass")) {
                continue;
            }
            Object res = readMethod.invoke(userQuery, null);
            if (res != null) {
                String columnName = getColumnName(readMethod.getName());
                queryWrapper.like(columnName, res);
            }

        }
    }

公共代码

上面反射和内省用到的公共代码：

    private 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();
    }