Question

I am writing a social networking web app with couchdb as backend. Currently I am maintaining user profiles as JSON docs.

My app has a friendship feature when one user will request other user and upon acceptance the friendship is solemnized. Besides friendship there is one way relationship called “follow” relationship as well.

I thought of creating a connection doc

{ 
source_user:'',
target_user:'',
source_follows_target:'',
target_follows_source:'',
..Similarly for friendship...
}

This doesn’t look right to me at all. Since the relationship exists between two exactly similar entities (users in this case) I dont thin the model should try to distinguish between source and target.

Answer 1

The fact that the relationship can be (or is always) symmetric doesn’t mean it necessarily has to be modelled as one logical relationship. I think it might more general to model the possibility of either, and then prevent one-way friendships in your application if you so desire.

In which case for each user you might have a set of users that they consider their friend (One -> Many). You could store a copy (or cache) of whether it is symmetric or not on each of these relationship objects to make it a bit more scalable.

A rough example of how a user object might look:

{
    "userId": 1,
    "friends": [{"userId": 2, "friendsBack": true | false}, ...]
}

Operations on these sets of users, e.g. intersections (friends in common), would then be a lot easier since they are accessed directly from the user object.