Creating capped collection in Meteor

[mattuuh7]

Is there an existing API for creating capped collection in Meteor? Thanks.

[estark37]

Hi @mattuuh7. There's an underscored (internal, not documented, not guaranteed to stick around in future releases) api for this right now; to create a capped collection on the server, you can do this:

var coll = new Meteor.Collection("myCollection");
coll._createCappedCollection(numBytes);

[mattuuh7]

Thanks!
It seems the current API only allow createCollection with size parameter, but not max number of documents. Maybe I will create a pull request to have that available as well.

[Slava]

@mattuuh7, Hi there,

consider reading these nuances about live updates to capped collection: https://github.com/meteor/meteor/blob/devel/packages/mongo-livedata/mongo_driver.js#L1161

[fgm]

FWIW, on 1.3.2.4, the link is now at https://github.com/meteor/meteor/blob/release-1.3.2.4/packages/mongo/mongo_driver.js#L1281

[yched]

Note - this seems to be broken after Meteor 1.11 and the update to mongodb driver 3.6.0 :

var coll = new Meteor.Collection("myCollection");
coll._createCappedCollection(3000);

This runs fine the very first time, when the collection doesn't actually exist. After that, you'll get an exception:

MongoError: a collection 'meteor.myCollection' already exists
     at Connection.<anonymous> (HOME/.meteor/packages/npm-mongo/.3.8.0.1u7psm6.649z++os+web.browser+web.browser.legacy+web.cordova/npm/node_modules/mongodb/lib/core/connection/pool.js:451:61)
     at Connection.emit (events.js:315:20)
     at Connection.EventEmitter.emit (domain.js:483:12)
     at processMessage (HOME/.meteor/packages/npm-mongo/.3.8.0.1u7psm6.649z++os+web.browser+web.browser.legacy+web.cordova/npm/node_modules/mongodb/lib/core/connection/connection.js:452:10)
     at Socket.<anonymous> (HOME/.meteor/packages/npm-mongo/.3.8.0.1u7psm6.649z++os+web.browser+web.browser.legacy+web.cordova/npm/node_modules/mongodb/lib/core/connection/connection.js:621:15)
     at Socket.emit (events.js:315:20)
     at Socket.EventEmitter.emit (domain.js:483:12)
     at addChunk (_stream_readable.js:295:12)
     at readableAddChunk (_stream_readable.js:271:9)
     at Socket.Readable.push (_stream_readable.js:212:10)
     at TCP.onStreamRead (internal/stream_base_commons.js:186:23) 

I suspect it's because of the "Changes in behavior of Db.prototype.createCollection" section in
https://github.com/mongodb/node-mongodb-native/releases/tag/v3.6.0

[yched]

As suggested in the Meteor forums, the following workaround works:

const db = Meteor.users.rawDatabase();
const collectionExists = db.listCollections({ name: 'myCollection' }).hasNext().await();
if (!collectionExists) {
  db.createCollection('myCollection', { capped: true, size: 3000 }).await();
}
const coll = new Mongo.Collection('myCollection');