code: public String update(Object obj) {
      Class<?> clazz = obj.getClass();
      PersistMeta meta = EntityUtil.getMeta(clazz);
      StringBuilder setting = new StringBuilder(32);
      int i = 0;
      for (Map.Entry<String, Field> kv : meta.getColumns().entrySet()) {
        if (isNull(kv.getValue(), obj)) {
          continue;
        }
  
        if (i++ != 0) {
          setting.append(',');
        }
  
        setting.append('`').append(kv.getKey()).append('`').append("=#{").append(kv.getValue().getName()).append('}');
      }
  
      return new SQL().UPDATE(getTableName(meta, obj)).SET(setting.toString()).WHERE("id=#{id}").toString();
    }
docs: 更新操作
  
  @param obj
  @return String