getUser method
读取用户
Implementation
User getUser(ObjectId uid) {
var item = _userMap[uid];
if (item == null) {
//创建一个临时用户实例
item = User(bsid: DbQueryField.hexstr2ObjectId(bsid), id: uid);
_userMap[uid] = item;
//获取未缓存的用户信息
userFetch(uids: [uid]);
}
return item;
}