Publish documents in a collection to a meteor client depending on the existence of a specific document in another collection (publish-with-relations)

Question

I have two collections

1. Offers (relevant fields: _id)
2. ShareRelations (relevant fields: receiverId and offerId)

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Answer 1

What you are looking for is a reactive join. You can accomplish this by directly using an observe in the publish function, or by using a library to do it for you. Meteor core is expected to have a join library at some point, but until then I'd recommend using publish-with-relations. Have a look at the docs, but I think the publish function you want looks something like this:

Meteor.publish('offersShared', function() {
  return Meteor.publishWithRelations({
    handle: this,
    collection: ShareRelations,
    filter: {receiverId: this.userId},
    mappings: [{collection: Offers, key: 'offerId'}]
  });
});

This should reactively publish all of the ShareRelations for the user, and all associated Offers. Hopefully publishing both won't be a problem.

PWR is a pretty legit package - several of us use it in production, and Tom Coleman contributes to it. The only thing I'll caution you about is that as of this writing, the current version in atmosphere (v0.1.5) has a bug which will result in a fairly serious memory leak. Until it gets bumped, see my blog post about how to run an updated local copy.

update 2/5/14:

The discover meteor blog has an excellent post on reactive joins which I highly recommend reading.