CODEWITHSUNDEEP
mongodbmongooseassociations
dsp_099
dsp_099

Reputation: 6121

How to properly "associate" multiple items with a mongoDB object without using relations per se?

Let's say I have a number of users who watch my application for notifications about things like social media activity account(s) of their choosing.

I'd like to be able to flash the users with an option to see the updates they've "missed" while they were offline.

If I store the Notification's MongoDB _id in a data object attached to the User model, I foresee a situation where they've signed up to ALL channels and have missed a few megabytes worth of updates, making the User object very large:

{ name: 'John'
  missedNotifications: [ /* 10 million items */ ]
}

On the other hand, Mongoose, though "supports" associations sort of runs into the same issue, except the many-to-many association would have this duplicate data in several places.

If the Notification object carries a list of users who've seen it or not, after a few years, scanning the entire Notifications collection may become very time-consuming.

Is there a third method for keeping track of who has seen what and amending the models properly?

Upvotes: 1

Views: 194

Answers (1)

B. Fleming
B. Fleming

Reputation: 7220

Instead of tracking the missed notifications, consider instead tracking the last notification received. MongoDB's ObjectIds are constructed as follows, as per the documentation:

  • a 4-byte value representing the seconds since the Unix epoch,
  • a 3-byte machine identifier,
  • a 2-byte process id, and
  • a 3-byte counter, starting with a random value.

Because of the way these ids are constructed, you can generally perform a $gt search on the _id field to retrieve all documents that were inserted after the previous known id (e.g. db.notifications.find({_id: {$gt: last_known_id}})).

In this way, you can retrieve all new notifications that were missed while only tracking one notification id. If you require tracking of multiple notification types and want to have greater granularity in your notification tracking, then just keep track of the last viewed document id for each type.

Upvotes: 1

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