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What's a database without any data? With mongodb-datasets you never worry about how to populate your MongoDB database with the data as you wish. Unlike a simple populator, mongodb-datasets is designed to offer you the maximum control of the data to be in your database.


To use the mongodb-datasets command, install mongodb-datasets globally:

$ npm install -g mongodb-datasets

To use the Javascript API, in your project directory:

$ npm install mongodb-datasets --save

A Simple Example


  "_id": "{{counter()}}",
  "name": "{{}}",
  "phones": [ 3, "{{}}" ],
  "title": "Software {{util.sample(['Engineer', 'Programmer'])}}"

Using the command:

$ mongodb-datasets test_schema.json -n 10 -o datasets.json

Or using the Javascript API:

var fs = require('fs'),
  es = require('event-stream'),
  assert = require('assert'),
  datasets = require('mongodb-datasets');
  .pipe(datasets.createGeneratorStream({size: 10})
  .pipe(es.writeArray(function (err, array) {
    assert.equal(10, array.length);


createGeneratorStream(options) creates a Transform stream, which consumes a Readable stream containing a template schema and produces a stream of generated documents in the form of Javascript objects.


  • size - the number of documents to be populated
  • schema - an object representing the template schema of your data. If present, the returned stream effectively behaves as a Writable stream.

Command line

You can also use mongodb-datasets in cli. Examples:

$ mongodb-datasets schema.json -n 10 -o dump.out
$ cat schema.json | mongodb-datasets -n 10 -o -
  -0          Path to a template schema file           [string]
  -n, --size  Number of documents to generate          [required]
  -o, --out   Path to output file. Use "-" for stdout  [required]
  --pretty    Whether to format results
  -h, --help  Show help message

Building your schema

The schema is a JSON or Javascript object which is used as the template of every single document to be inserted into MongoDB database. The following content in this section discusses how to specify the value of each name/value pair of the object.


The value can be any primitive data types, such as boolean, number, array, and object. When the value is a string, it can be used to evaluate Javascript expressions. All string segments intended to be treated as expressions must be surrounded by {{ <expr> }}. A mix of regular string and expressions are allowed, whereas a mix of different types is not. Some examples:

  • { "boolean": true }
  • { "brackets_parade": [ { 1: { 2: [ { 3: 3 } ] } } ] }
  • { "mix": "1 + 1 = {{ 1+1 }}" }

Random data

This project uses chance.js and faker.js as the internal random data generator. To invoke them, use faker.<method> and chance.<method>:

  • { "use_chance": "{{{ gender: 'female' }) }}" }
  • { "use_faker": "{{ faker.Company.catchPhrase() }}" }

Type conversion

Maybe you've already noticed. It's not very useful to generate a string from "{{chance.year()}}" which is expected to apply commands such as $gte. Since its MongoDB-specific nature, the package currently supports common bson types as in bson module, such as Number, Timestamp, Date, and ObjectID. Note that once conversion is triggered, the target object will be the only produced content. Some examples:

  • { "date": "{{ Date( }}" } becomes ISODate(...) in MongoDB
  • { "two": "{{ Number(1) + Number(1) }}" } produces { "two": 1 }

Document-level scope

You can make use of this keyword in expressions to get access to values of other name/value pairs. But its behavior is different from the default this in a Javascript object in the sense that all properties must correspond to a name/value pair. Using values not yet generated is also supported, and the invoked values will not be generated more than once per inserted document. You can also access a field's parent using this._$parent.

  • { "one": 1, "two: "{{ Number( + 1) }}" }
  • { "first_name": "{{ }}", "name": { "first": "{{ chance.first() }}" } } produces consistent result.
  • { "echo": {{ Object.keys(this) }} } returns { "echo": [ "echo" ] }
  • { "1": { "2": "{{ this._$parent.3 }}" }, "3": "{{ chance.d6() }}" }

Field visibility

You also have control on the visibility of each field. By default, fields with name starting with _$ are hidden. To toggle the visibility, simply call show(boolean) or hide(boolean) anywhere in the target field's expression. Note that while hidden one can still access its newly generated value.

  • { "_$digit": 3, "lat": "{{ chance.latitude({fixed: this._$digit}) }}", "lng": "{{ chance.longitude({fixed: this._$digit}) }}"}
  • { "temperature": "{{ util.random(40, 130) }}", "warning": "Too hot! {{ hide(this.temperature < 100) }}" }

Utility methods

We are happy to add more methods in a prompt manner should you find any could be potentially helpful. Currently we have:

  • _$size - the total number of generated docs in the current run
  • _$index - the index of the current document, starting from 0
  • counter([id], [start], [step]) - the underlying counts are accessble anywhere in the outmost document so that you can use the same counter consistently regardless of its position
    • id - the index of the counter to use, default is 0
    • start - the first count, default is 0
    • step - increment of each count, default is 1
  • util.sample(list, [n]) - identical to underscore.js


  • Due to the use of underscore.js, _ is accessible from within the template schema. Its many powerful methods may cause unwanted effects if used unchecked.
  • A lot of efforts were made to avoid exposing internal variables, but there is still one not properly handled, such as _state. Please do not mess with it.
  • Expressions provided by users are directly evaluated without any error checking, which may cause the program to crash without supplying much helpful information to users

Purpose of this project

With the explosion of data volume and availability, users are transitioning their focus to analysis and data-mining on these vast datasets. We believe MongoDB is ideally positioned to provide the backbone to meet these market needs. While several users have already begun to exploit this, it requires substantial sunk costs including mapping the aggregation framework to their current mental model, designing efficient schemas, and acquiring datasets for prototyping. Work to humanize the aggregation framework is already underway. We believe supplying users with example schemas for common use cases, such as user activity streams, time series data, and entity management, and more importantly, corresponding datasets for prototyping will establish MongoDB as a leader in this emerging market.

Change log

0.1.0 - Jul. 23, 2014

First release!

0.1.1 - Jul. 23, 2014

  • Fixed bug that causes mongodb-datasets command crash
  • Updated README to include all features

0.1.3 - Jul. 24, 2014

  • Fixed bug that causes inconsistent content if this.<embedded doc> is used

0.1.4 - Jul. 28, 2014

  • Changed Double to Number to hide Javascript's Number constructor
  • Added _$index
  • Made the former _$size() a property _$size

Changed not yet published

branch:API - Jul. 29, 2014

  • Output nice formatted json array with flag --pretty enabled
  • Mapped chance and faker's random functions to higher level API of datasets. Please consult comments in `lib/schema/context.js' for detailed usage.

branch:arrayField - Jul. 31, 2014

  • New syntax for defining arrays in template schema
  • All configured arrays must conform to the format:
    • [ "{{_$config}}", {/*options*/}, <content>, /*optionally*/ <more content...> ]
  • Arrays whose first element is not {{_$config}} are treated as ordinary arrays
    • multiple elements are ok, [ '{{}}', '{{chance.age()}}' ]
    • different types are ok [ true, 3, { doc: 'doc' }, [ "array" ]]
  • Supported options:
    • size - can be a number or an array of two numbers ([min, max]). the number of times the contents will be repeated