Publishing/subscribing multiple subsets of the same server collection

Posted by matb33 on Stack Overflow See other posts from Stack Overflow or by matb33
Published on 2012-09-28T01:36:36Z Indexed on 2012/10/02 3:38 UTC
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How does one go about publishing different subsets (or "views") of a single collection on the server as multiple collections on the client?

Here is some pseudo-code to help illustrate my question:

items collection on the server

Assume that I have an items collection on the server with millions of records. Let's also assume that:

  1. 50 records have the enabled property set to true, and;
  2. 100 records have the processed property set to true.

All others are set to false.

items:
{
    "_id": "uniqueid1",
    "title": "item #1",
    "enabled": false,
    "processed": false
},
{
    "_id": "uniqueid2",
    "title": "item #2",
    "enabled": false,
    "processed": true
},
...
{
    "_id": "uniqueid458734958",
    "title": "item #458734958",
    "enabled": true,
    "processed": true
}

Server code

Let's publish two "views" of the same server collection. One will send down a cursor with 50 records, and the other will send down a cursor with 100 records. There are over 458 million records in this fictitious server-side database, and the client does not need to know about all of those (in fact, sending them all down would probably take several hours in this example):

var Items = new Meteor.Collection("items");

Meteor.publish("enabled_items", function () {
    // Only 50 "Items" have enabled set to true
    return Items.find({enabled: true});
});

Meteor.publish("processed_items", function () {
    // Only 100 "Items" have processed set to true
    return Items.find({processed: true});
});

Client code

In order to support the latency compensation technique, we are forced to declare a single collection Items on the client. It should become apparent where the flaw is: how does one differentiate between Items for enabled_items and Items for processed_items?

var Items = new Meteor.Collection("items");

Meteor.subscribe("enabled_items", function () {
    // This will output 50, fine
    console.log(Items.find().count());
});

Meteor.subscribe("processed_items", function () {
    // This will also output 50, since we have no choice but to use
    // the same "Items" collection.
    console.log(Items.find().count());
});

My current solution involves monkey-patching _publishCursor to allow the subscription name to be used instead of the collection name. But that won't do any latency compensation. Every write has to round-trip to the server:

// On the client:
var EnabledItems = new Meteor.Collection("enabled_items");
var ProcessedItems = new Meteor.Collection("processed_items");

With the monkey-patch in place, this will work. But go into Offline mode and changes won't appear on the client right away -- we'll need to be connected to the server to see changes.

What's the correct approach?

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