Performing complex joins in MongoDB using multiple sub documents

Question

Performing complex joins in MongoDB using multiple sub documents

I am managing two unique collections,

Users collection:

{
    "userId": 1,
    "name": 'Alice',
    "profile": 'alice.png'
},
{
    "userId": 5,
    "name": 'Bob',
    "profile": 'bob.png'
},
{
    "userId": 10,
    "name": 'Carol Smith',
    "profile": 'carol.jpg'
}

Posts collection:

{
    "postId": 3,
    "userId": 1,
    "postContent": "Lorem Ipsum is simply dummy text of the printing and typesetting industry.",
    "comments": [
        {
            "comment": "Great post!",
            "commentedBy": 5,
        },
        {
            "comment": "Love this!",
            "commentedBy": 10,
        }
    ],
}

How do I retrieve post details along with user information for each post and user details for each comment using a single mongoose query?

javascript mongodb mongoose

Answer 1

Answer №1

If you're looking to connect your collections in Mongoose, the "populate" method is a great tool to use. Check out the documentation here: https://mongoosejs.com/docs/populate.html

This feature allows you to easily link your collections in the schema definition and query and populate all related collections with just one query, like so:

Posts.findOne({ postId: 1 }).populate('user')

For more information on how to set up your Schemas, make sure to visit the link provided above.

Answer 2

If you're looking to connect your collections in Mongoose, the "populate" method is a great tool to use. Check out the documentation here: https://mongoosejs.com/docs/populate.html

This feature allows you to easily link your collections in the schema definition and query and populate all related collections with just one query, like so:

Posts.findOne({ postId: 1 }).populate('user')

For more information on how to set up your Schemas, make sure to visit the link provided above.

Answer 3

Answer №2

To achieve this, you can utilize the combination of $aggregate and $lookup

db.posts.aggregate(
  [
    {
      $lookup:
      {
        from: "users",
        localField: "userId",
        foreignField: "userId",
        as: "users"
      }
    }
  ]
).pretty()

The result will be displayed in the following format:

{
        "_id" : ObjectId("5ecceb468d4390391825b79d"),
        "postId" : 1,
        "userId" : 1,
        "postContent" : "Lorem Ipsum is simply dummy text of the printing and typesetting industry.",
        "comments" : [
                {
                        "comment" : "sample comment",
                        "commentedBy" : 2
                },
                {
                        "comment" : "Another sample comment",
                        "commentedBy" : 3
                }
        ],
        "users" : [
                {
                        "_id" : ObjectId("5ecceb168d4390391825b79a"),
                        "userId" : 1,
                        "name" : "John",
                        "profile" : "john.png"
                }
        ]
}

Information sourced from MongoDB

https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/

Answer 4

To achieve this, you can utilize the combination of $aggregate and $lookup

db.posts.aggregate(
  [
    {
      $lookup:
      {
        from: "users",
        localField: "userId",
        foreignField: "userId",
        as: "users"
      }
    }
  ]
).pretty()

The result will be displayed in the following format:

{
        "_id" : ObjectId("5ecceb468d4390391825b79d"),
        "postId" : 1,
        "userId" : 1,
        "postContent" : "Lorem Ipsum is simply dummy text of the printing and typesetting industry.",
        "comments" : [
                {
                        "comment" : "sample comment",
                        "commentedBy" : 2
                },
                {
                        "comment" : "Another sample comment",
                        "commentedBy" : 3
                }
        ],
        "users" : [
                {
                        "_id" : ObjectId("5ecceb168d4390391825b79a"),
                        "userId" : 1,
                        "name" : "John",
                        "profile" : "john.png"
                }
        ]
}

Information sourced from MongoDB

https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/

Performing complex joins in MongoDB using multiple sub documents

Users collection:

Posts collection:

Answer №1

Answer №2

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