Meteor - MongoDB Object Array Property Selector

Introduction

One slightly confusing question that I get asked sometimes and I see around the internet is how to select a document from a collection based on a property in an array of objects.

Suppose we have a SimpleSchema like so:

Schema = {};

Schema.Task = new SimpleSchema({
  name: {
    type: String,
    label: "Task Name"
  },
  tags: {
    type: [Object],
    label: "Tags",
  },
  "tags.$.name": {
    type: String
  },
  "tags.$.rank": {
    type: Number
  }
});

Tasks.attachSchema(Schema.Task);

And we have inserted the following document:

Tasks.insert({
  name: "Write Meteor Tutorial",
  tags: [
    {
      "name": "Meteor",
      "rank": 0
    },
    {
      "name": "Tutorial",
      "rank": 1
    }
  ]
});

And we want to select all the tasks that have a tag with the name “Meteor”. We can use the following syntax to perform this task:

Tasks.find({
  "tags.name": "Meteor"
});

Notice how we did not include the $ symbol that we used when specifying our SimpleSchema. Additionally if we only want to select the tags and not the entire Tasks object we can use a fields option.

Tasks.find({
  "tags.name": "Meteor"
}, {
  fields: { "tags.$": 1}
});

The differing syntax may seem a bit confusing, but once you get the hang of it you can create some pretty powerful and complex schemas and selectors. Hope this helps anyone running into this problem!