Graphml-views-mongodb

A library that enable views for MongoDB based on GraphML, which generates collections from MongoDB datasources by given graphml files.

Installation

$ npm install graphml-views-mongodb --save

Why create this?

The original MongoDB doesn't support view like CouchDB and other SQL-Like database. And it supports the following ways to make relations between multiple collections:

• embed documents
• DBRef type to reference to other database

weakness of the above ways to relate collections

The embed documents even though has a avilability for retrieving data, but lack of consistency on writing data on the embeded documents.

The DBRef is not recommended way to take the role of expressing relations, we should use it to reference a value to another database that maybe in other system.

about loopback.io

The next context is about Loopback, the framework to replace the role of Parse and LeanCloud, the framework abstracts most popluar databases into the same one schema, and it support rich relations as below:

• one-to-one
• one-to-many

That's good, but not enough, because Loopback's scoping/joining syntax is such complicated so that the request URLs would become too long and unreadability. So sometimes, the truth is that we want a collection is for a view, and we just query it directly from the collection without scoping and joining. At the same time, for write operations, we hope that model-based would be used and it will updates data to the view collections.

why GraphML?

In starting this project, we tried JSON, YAML and TOML to express what fields would be in our view collection, but they are almost out after having a try on GraphQL, and then we found GraphQL is the QL for querying, so we, the WeFlex team decoded to rewrite a new marked language based on basic of GraphQL, that's the GraphML.

To express a view, you just need the following:

User {
  username,
  nickname,
  sex,
  country,
  orgs {
    name
  },
  followings {
    username,
    avatarUrl
  },
  followers {
    username,
    avatarUrl
  }
}

Then you will get document:

{
  "_id": "id",
  "username": "yorkie",
  "nickname": "yorkie",
  "sex": "female",
  "country": "internet",
  "orgs": [
    {
      "_id": "weflex_id",
      "name": "weflex"
    }
  ],
  "followings": [
    {
      "_id": "following_id",
      "name": "substack",
      "avatarUrl": "image url"
    }
  ],
  "followers": [
    {
      "_id": "follower_id",
      "name": "scott",
      "avatarUrl": "image url"
    }
  ]
}

How it works

The Graphml-views-mongodb does parse a GraphML file and get fields collection that you want to include from the source collections, and read the relations from pre-defined Loopback models, and generate the complete documents.

API

• parseGraphs(models, dataSources)
  • models {Array} the object returned from loopback
  • dataSources {Object} the object to take dataSources
    • rest {MongoDB} the resouce database instance
    • view {MongoDB} the view database instance
  • dir the dirname path

License

MIT @ WeFlex, Inc.