利用反射生成 MyBatisPlus中QueryWrapper动态条件 #yyds干货盘点#

Posted 2022-02-17 梁云亮

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();