MongoDB: You're doing it wrong!

The main reason we use NoSQL, typically, MongoDB, is to store and query big data in a scalable way.

Document Reference Pattern.

When we think of modelling NoSQL in a RDBMS way, we'll need to reference documents in other collections to link or join 2 pieces of related data.

// document in organization collection
{
   _id: "google",
   name: "Google"
}

// document in user collection
{
   _id: "john",
   name: "John Smith",
   organization_id: "google"

}

{
   _id: "jeff",
   name: "Jeff Brown",
   organization_id: "google"

}

So to find an organization and all the users in one query we need to use the aggregation framework:

db.getCollection('organization')
.aggregate([
  {
    $match: { _id: "google"}
  },
  {
    $lookup: {
        from: "user",
        localField: "_id",
        foreignField: "organization_id",
        as : "users"
    }
  }
])

Result

{
    "_id" : "google",
    "name" : "Google",
    "users" : [ 
        {
            "user_id" : "john",
            "name" : "John Smith",
            "organization_id" : "google"
        },
        {
            "user_id" : "jeff",
            "name" : "Jeff Brown",
            "organization_id" : "google"
        }
    ]
}

When using joins, our queries don't scale. The computation cost rises as data footprint increases.

Adjacency list pattern

Let's try the Adjacency list pattern for storing data:
Use one collection for all data. Let's call it "DATA"

//organization document in DATA collection
{
    "_id": "org#google",
    "name": "Google",
}
{
    "_id": "org#microsoft",
    "name": "Microsoft",
}
{
    "_id": "org#apple",
    "name": "Apple",
}

//user document in DATA collection
{
   _id: "org#google#user#john",
   name: "John Smith"
}
{
   _id: "org#google#user#jeff",
   name: "Jeff Brown"
}
{
   _id: "org#apple#user#tim",
   name: "Tim Cook"
}

Let's try to find an organization and all the users in one query.

db.getCollection('DATA').find({_id: {$regex: /^org#google/}})

The query finds all documents in the DATA collection starting where _id starts with "org#google"

Result


{
    "_id" : "org#google",
    "name" : "Google"
}

{
    "_id" : "org#google#user#jeff",
    "name" : "Jeff Brown"
}

{
    "_id" : "org#google#user#john",
    "name" : "John Smith"
}

We can retrieve the same data without a join, without adding indexes, without using the aggregation framework

Blog

MongoDB: You're doing it wrong!

Paul Allies

Document Reference Pattern.

Result

Adjacency list pattern

Result

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