Looked over the MongoDB and Mongoose docs and can't see if this is even possible. I'll tell you up front I've written no code attempting to do this yet, because I can't find anything to hook into for it.
What I'm looking for is after setting a TTL expiry on a MongoDB document (inserted via Mongoose in case that matters), I'd like the application to get a notification when the document is ejected from the collection. Is there a way to do that native to MongoDB, or will I have to do something on my own (e.g. polling)?
There are no server-side hooks for your application to get notified when MongoDB documents are removed via a TTL index.
However, a TTL index is just a date-based index used by a server-side TTL thread that wakes up every minute and deletes new documents matching the expiry criteria.
If you want to add some sort of on-delete hook, I would suggest writing your own expiry script and running this as a scheduled task via cron or equivalent. This script could first run a query to find matching documents ready to be expired, and then implement whatever notification your application needs before the documents are actually deleted.
Here's a mongoose plugin that can help you. It implements TTL feature and calls onReap function each time reaper being executed.
var ttl = require('mongoose-ttl');
var schema = new Schema({..});
schema.plugin(ttl, {
ttl: 'the time each doc should live in the db (default 60 seconds)',
interval: 'how often the expired doc reaper runs (default 5 mins)',
onReap: 'callback passed to reaper execution'
});
Should mention that this plugin does not utilize native MongoDB TTL feature.