Typegoose Cursor-based Pagination

!Build

This module aids in implementing "cursor-based" pagination using Mongo range queries or relevancy-based search results. It is based on the mongo-cursor-pagination package but has a dedicated mongoose plugin (which keeps instance methods etc.) and support for Typegoose out of the box.

Demo project

A demo project can be found here: https://github.com/ExtraBB/typegoose-cursor-pagination-demo

Background

See this blog post for background on why this library was built.

API Pagination is typically implemented one of two different ways:

1. Offset-based paging. This is traditional paging where skip and limit parameters are passed on the url (or some variation such as page_num and count). The API would return the results and some indication of whether there is a next page, such as has_more on the response. An issue with this approach is that it assumes a static data set; if collection changes while querying, then results in pages will shift and the response will be wrong.

2. Cursor-based paging. An improved way of paging where an API passes back a "cursor" (an opaque string) to tell the caller where to query the next or previous pages. The cursor is usually passed using query parameters next and previous. It's implementation is typically more performant that skip/limit because it can jump to any page without traversing all the records. It also handles records being added or removed because it doesn't use fixed offsets.

This module helps in implementing #2 - cursor based paging - by providing a method that make it easy to query within a Mongo collection. It also helps by returning a url-safe string that you can return with your HTTP response (see example below).

Here are some examples of cursor-based APIs:

* Twitter
* Stripe
* Facebook

Install

npm install typegoose-cursor-pagination --save

Usage

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The plugin accepts the following options:

``typescript
export interface IPluginOptions {
dontReturnTotalDocs?: boolean; // Don't return the total number of results for the given query
dontAllowUnlimitedResults?: boolean; // Don't allow unlimited results
defaultLimit?: number; // A default limit instead of 10
}
`

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findPaged() will return ordered and paged results based on a field (sortField) that you pass in.

$3

Call findPaged() with the following parameters:
- params {IPaginateOptions} (The paginate options)
- _query {Object} (A mongo query)
- _projection {Object} (A mongo projection)
- _populate {string | PopulateOptions | (string | PopulateOptions)[]} (A mongoose population object or array)

`typescript
interface IPaginateOptions {
limit: Number; // The page size. Set 0 for no limit.
sortField: String; // The field name to query the range for. The field must be:
/*
1. Orderable. We must sort by this value. If duplicate values for paginatedField field
exist, the results will be secondarily ordered by the _id.
2. Indexed. For large collections, this should be indexed for query performance.
3. Immutable. If the value changes between paged queries, it could appear twice.
4. Complete. A value must exist for all documents.
The default is to use the Mongo built-in '_id' field, which satisfies the above criteria.
The only reason to NOT use the Mongo _id field is if you chose to implement your own ids.
*/
sortAscending: Boolean; // True to sort using paginatedField ascending (default is false - descending).
next: String; // The value to start querying the page.
previous: String; // The value to start querying previous page.
}
`

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The response object of findPaged() is as follows:

`typescript
interface IPaginateResult {
hasNext: Boolean // hasNext is true if there is a next page
hasPrevious: Boolean // hasPrevious is true if there is a previous page
next: String // next is the cursor for the next page
previous: String // previous is the cursor for the previous page
totalDocs: Number // totalDocs is the total amount of docs for the query
docs: T[] // docs are the resulting documents for this page
}
`

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aggregatePaged() will return ordered and paged results based on a field (sortField) that you pass in using MongoDB aggregate, which allows for more complicated queries compared to simple findPaged().

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Call aggregatePaged() with the following parameters:

- options {IPaginateOptions} (The paginate options)
- _pipeline {PipelineStage[]} (The aggregation pipeline array)

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Same as for findPaged()

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Create your typegoose model as follows:

`js
import paginationPlugin, { PaginateModel } from 'typegoose-cursor-pagination';
import { prop, getModelForClass, plugin, index } from "@typegoose/typegoose";
import mongoose from "mongoose";

@plugin(paginationPlugin)
@index({ email: 1 })
export class User {
@prop({ required: true })
name: string;

@prop({ required: true })
email: string;
}

export const UserModel = getModelForClass(User, { existingMongoose: mongoose }) as PaginateModel;;
`

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Use the findPaged() method as follows:

`js
import { Request, Response, NextFunction } from "express";
import { IPaginateOptions } from "typegoose-cursor-pagination";
import UserModel from "./User";

export async function getUsers(req: Request, res: Response, next: NextFunction) {
const options: IPaginateOptions = {
sortField: "email",
sortAscending: true,
limit: 10,
next: "WyJuZXdAdG9rYXMubmwiLHsiJG9pZCI6IjVjNGYxY2U1ODAwYzNjNmIwOGVkZGY3ZCJ9XQ"
};

const query = {}; // Your specific query
const projection = {}; // Your desired projection
const populate = [] // Your needed population


const users = await UserModel.findPaged(options, query, projection, populate);
res.send(users)
}
``