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mongodb-cursor-pagination

v1.10.0

Published

Cursor-based pagination for MongoDB

Downloads

434

Readme

mongodb-cursor-pagination npm

GitHub Workflow Status code style: prettier

Cursor-based pagination for MongoDB.

Based on mongo-cursor-pagination but written from scratch in TypeScript with an API that resembles the cursor connection spec from Relay.

The problem

By default, MongoDB allows us to paginate results with limit and skip. That's known as offset-based pagination. It's definitely the simplest way to paginate, but in some situations it's not very stable.

Imagine you have a restaurant software showing a list of orders paginated with limit: 3 and skip: 0:

  • { _id: ObjectId, number: 53 }
  • { _id: ObjectId, number: 52 }
  • { _id: ObjectId, number: 51 }

Nice, so far so good. Now, when you click the button to see the next page, here's what you'd expect to see (limit: 3, skip: 3):

  • { _id: ObjectId, number: 50 }
  • { _id: ObjectId, number: 49 }
  • { _id: ObjectId, number: 48 }

Pretty reasonable, right? By using skip: 3 we're basically telling MongoDB hey, I want to skip orders #53, #52 and #51.

But imagine a new order (#54) arrived while we were staring at the 1st page. In that case, querying with skip: 3 would actually give us:

  • { _id: ObjectId, number: 51 }
  • { _id: ObjectId, number: 50 }
  • { _id: ObjectId, number: 49 }

That's because in this new scenario we're actually telling MongoDB hey, I want to skip orders #54, #53 and #52.

If you have any trouble to fully comprehend what's happening here, try to imagine the following scenario yourself:

  • You've queried the 1st page with limit: 3 and skip: 0.
  • While you are looking at the 1st page, 200 new orders arrive.
  • What will you see when you try to query the 2nd page with limit: 3 and skip: 3?

The solution

So how can we make sure that the 2nd page always start from the order #50 no matter how many orders have been received in the meantime? Well, a naive approach would be like:

collection
  .find({ number: { $lt: 51 } }
  .sort({ number: -1 })
  .toArray()

And that's somewhat what this lib does but in a much more robust way.

For a more thorough explanation I highly recommend reading the excellent blog post from Mixmax. You can also read the source code — I tried to add helpful comments.

Installation

npm i mongodb-cursor-pagination
yarn add mongodb-cursor-pagination

Usage

import { MongoClient } from 'mongodb'
import { findPaginated } from 'mongodb-cursor-pagination'

const client = await MongoClient.connect(uri)
const db = client.db()
const collection = db.collection('users')

let skipFirst20

// Get third page
skipFirst20 = await findPaginated(collection, {
  first: 10,
  skip: 20
})


let result

// Get first page
result = await findPaginated(collection, {
  first: 10
})

// Go to second page
result = await findPaginated(collection, {
  first: 10,
  after: result.pageInfo.endCursor,
})

// Back to first page
result = await findPaginated(collection, {
  last: 10,
  before: result.pageInfo.startCursor,
})

API

findPaginated

Runs a paginated query on top of Collection#find.

Arguments

  • collection: The MongoDB collection.
  • params:
    • Properties:
      • first: How many documents to get (forwards pagination).
      • after: The cursor (forwards pagination).
      • last: How many documents to get (backwards pagination).
      • before: The cursor (backwards pagination).
      • query: The query to be passed to Collection#find.
      • sort: The sort to be passed to Collection#find.
      • projection: The projection to be passed to Collection#find.

Returns

  • edges: An array with the contents of the page.
    • Properties:
      • node: The document.
      • cursor: An opaque string pointing to this document in the context of this query. It can be passed to parameters after or before to get a page starting after or before this document.
  • pageInfo:
    • Properties
      • startCursor: The cursor of the first document in this page.
      • endCursor: The cursor of the last document in this page.
      • hasPreviouPage: Whether there's another page before this one.
      • hasNextPage: Whether there's another page after this one.

aggregatePaginated

Runs a paginated aggregation on top of Collection#aggregate.

Arguments

  • collection: The MongoDB collection.
  • params:
    • Properties:
      • first: How many documents to get (forwards pagination).
      • after: The cursor (forwards pagination).
      • last: How many documents to get (backwards pagination).
      • before: The cursor (backwards pagination).
      • pipeline: The pipeline array to be passed to Collection#aggregate.
      • sort: The sort to be passed to Collection#aggregate.

Returns

  • edges: An array with the contents of the page.
    • Properties:
      • node: The document.
      • cursor: An opaque string pointing to this document in the context of this query. It can be passed to parameters after or before to get a page starting after or before this document.
  • pageInfo:
    • Properties
      • count: The number of nodes fetched for current page.
      • totalCount: The number of nodes available based on query.
      • startCursor: The cursor of the first document in this page.
      • endCursor: The cursor of the last document in this page.
      • hasPreviouPage: Whether there's another page before this one.
      • hasNextPage: Whether there's another page after this one.

License

Released under the MIT License.