如何按最新活动查询下一个对话排序？

Question

I'm implementing a chat system like Facebook, I have two tables, one is messages and one is conversations:

conversations
id  |  peoples         | updatedAt
1      [user1, user2]    Today 8:10 PM 
2      [user1, user2]    Today 9:03 PM
3      [user1, user2]    Today 5:01 PM
4      [user1, user2]    Today 5:01 PM
5      [user1, user2]    Today 5:01 PM
6      [user1, user2]    Today 4:01 PM

When a user sent a message, I update the field updatedAt of conversations by current time so I can query the lastest conversations, but the problem here is how I continue to query the latest conversation after that? For example, first I will query two latest conversation, as you can see here is a conversation with id 2 and 1 will return, then I save the updatedAt value of id 1 (the value is Today 8:10 PM ) so I can continue query latest conversation with the condition {updatedAt: {$lte: Today 8:10 PM} and take only 2 conversations like first and it will return conversation with id 3,4 and I save the updatedAt field of id 4 (value is Today 5:01 PM ), continue query with same condition: {updatedAt: {$lte: Today 5:01 PM} it will return conversation with id 3,5 , the id 3 I have query before I don't need it, so how to avoid this? I use mongodb as database

Answer 1

Probably you need to keep updatedAt as timestamp.
Mongodb has appropriate type for it. You can see more at docs by this link