MongoDB: best design for messaging app [duplicate]
Based on your example data for the messaging app, what you could do is having two collections: Conversation and Messages. Where the relationship is one Conversation have many Messages.
Conversation:{ id: 123 participants: ['john', 'marry'],}Message:{ sender: 'john', content: 'howdy', time_created: new Date(), converstationId: 123},{ sender: 'marry', content: 'good u', time_created: new Date(), converstationId: 123 },Creating a new document message would be better in this case, as you can then have two applications (1 for john and 1 for marry) without handling the possibility of the two of them updating the same document.They just happens to be sharing the same conversation session.
Also, if a conversation is a single document, you might end up with a very large document. (Document growth concern)
You can find out more about data modelling for this mongodb doc
http://docs.mongodb.org/manual/core/data-modeling-introduction/
Also see MongoDB: Socialite for examples/discussion for social network use case.
Hope it helps. Cheers.