I am trying to model a simple chat application that has “conversations” that contain “messages”. Each message being a separate document.
The “messages” documents are not synchronized, they serve as a local cache for messages (among other things) that are delivered through XMPP.
I am having trouble modelling the view that shows conversations ordered by “last message” like any messenger app does. Currently we have a separate document that only contains the conversation ID and a “last message date” property that is updated for every single message. This way we can create a really simple view that emits the last date.
Can we find a schema where we don’t have this third document type and have a view that will emit values in a way that allows us to order the conversations by “last message” ?
Do you mind adding your current document model to this conversation? It will help in coming up with a solution as everyone will be able to see our thought process.
Without getting ahead of myself, have you thought about using a composite key where the first part is say a document id and the second part is say a timestamp of when the message was sent? Then you can create a query around that view and order it.
Let’s start with your current document model and we’ll work our way up
Thank you Traun. It does indeed give me a direction on where to start.
However, I don’t think this is the best solution. It might be! Maybe someone who already did it can share his feelings about this.
The view/query maps the messages and uses the reduce function to fetch the latest message and the latest date from each chat room: see the code. This means that every time they want to display the chat rooms, they have to reduce all the message key/value pairs in order to get the result.
Now, I understand that it is a good case to show the use of map/reduce in an example app, but in the real world, where we might have thousands of messages, is it really efficient to reduce every time?
_id: auto-generated
type: "conversation"
name: String
participants: [ID] // List of user IDs
_id: auto-generated
type: "message"
conversation: ID // "conversation"
from: ID // User
to: ID // User
date: Date
message: String
_id: auto-generated
type: "conversation-metadata"
conversation: ID
lastActivity: Date
lastMessage: String
Currently, each time a message is sent/received, I update the conversation-metadata with an updated view of the conversation. The conversation documents are synced between the participants, the conversation-metadata documents are only stored locally to prevent unnecessary traffic. Also, as I said in my OP, message document are only used as a cache. They are delivered through XMPP.
We can create a view of message documents with keys like [conversation, lastDate] like @nraboy suggests. However, I am not sure how to get the ordered list of conversations? Grouping using the first key, then reducing with the last element in each group? As I said in my reply to @traun, it means that the reduce function has to run each time with all the emit key/value pairs. Is that really efficient?
