How to publish a mongodb array length as an additional collection field?

Question

I have a mongodb collection with the following fields:

• _id
• name (string)
• [items] (array of string)
• secret (boolean)

I want to publish the all the _id, name fields and the item array length only (excluding the secret field) where the secret field is true.

I have read somewhere that I can add additional document properties in my find query, but my google foo does not work.

Here is what my publish method looks like without the additional items_count property:

Meteor.publish("all_items", function() {
    return myItems.find(
                 {secret: true},
                 {fields:
                   {_id:1,name:1}
                 });
        });

How can I create an additional field from the [item] length in my publication?

EDIT : it seems that I need to use an aggregate function and the $project operator. And it is not supported by meteor.

Can anyone confirm this to me (ie it is the only option and it is not supported)?

Answer 1

You can add aggregation framework support to Meteor , and then use a simple aggregation pipeline with $project stage as you mentioned, like to following:

myItems.aggregate(
    [
       {$match: {secret: true}},
       {$project: {_id: 1, name: 1, items_count: {$size: '$items'}}}
    ]
)