@hallysonh/koa-pageable

Koa Pageable

• About
• Overview
  • Request
    • Query parameters
      • Pageable
      • Sort
    • Errors
  • Response
    • All Page types
      • Map Method
    • ArrayPage
    • IndexedPage
    • IndexablePage
    • Output Format
      • Non-Indexed
      • Indexed
• Getting Started
  • Installation
    • npm
    • yarn
  • Requirements
  • Examples
    • Router
    • Data Access
• API Documentation

About

koa-pageable is middleware for pagination in Koa inspired by Spring Data's Pagination support.

It allows clients of your API to easily request subsets of your data by providing query parameters to specify the amount, order, and formatting of the requested data. For instance, if you had an endpoint /people backed by a data store containing 1000 people records, koa-pageable allows a client to request the data be broken up into 10 person pages, and to receive 2nd page of people sorted by their lastname (GET /people?page=1&size=10&sort=lastname)

Overview

Request

Query parameters

When enabled this middleware parses request query parameters from ctx.query into an instance of Pageable.

These values are:

Parameter	Default Value	Description
page	0	The 0-indexed page to be retrieved
size	10	Maximum number of elements to be included in the retrieved page
sort	undefined	Properties that should be sorted, in the specified order. Properties are separated by a , and directions are separated with a :. Valid directions are asc and desc and if not specified, direction defaults to asc. For example to sort by lastname ascending, then firstname descending: ?sort=lastname,firstname:desc
indexed	false	If the underlying content supports it (i.e. has an id property) return results in indexed format. Which is an array of ids and a map of {id : content item}

Pageable

The Pageable object created from the query parameters contains two integers, page & size, an optional Sort instance, and an indexed boolean. This pageable instance should be passed to your data access layer, and its content should be used to restrict the returned data to the data specified by the pageable.

Sort

Sort is a collection of property and direction( asc or desc) pairs. Each sort instance has a forEach(callback(property,direction)) method that invokes callback for each property/direction pair in the sort

Errors

If the page or size query parameter are not specified as valid numbers, a NumberFormatError will be thrown. If the sort direction is specified as anything other than asc or desc (e.g. sort=lastName:foo) then an InvalidSortError will be thrown.

Response

The data returned from a using this middleware should be an instance of a subclass of Page.

All Page types

All Page types contain the following properties:

Property	Description
number	The number of the current page (should match pageable.page)
size	The number of elements requested to be included in the current page (should match pageable.size)
numberOfElements	The number of elements actually returned in this page. If < size, indicates that this is the last page
totalElements	Total number of elements available
totalPages	Total number of pages available
sort	The sort criteria (should match pageable.sort)
first	True if this is the first page
last	True if this is the final page

You may have noticed that the above list does not define a property containing the actual content to be returned. This is because there are multiple Page implementations which represent the actual content items in different formats.

Map Method

All Page types also provide a map(iteratee) method. This method iterates over each content item in the page and invokes iteratee with the content item as the argument, allowing easy transformation from a Page<X> to a Page<Y>. This is useful, for instance, if you wish to return a different object from your router than the type returned from your data layer.

ArrayPage

A Page of content items represented as an array. An ArrayPage contains all of the properties above plus:

Property	Description
content	Array of content ordered as per pageable.sort

IndexedPage

An IndexedPage represents the returned content as an array of ids and a corresponding index, which is a map of {id: content item}. An IndexedPage contains all of the standard page properties plus:

Property	Description
ids	Array of ids ordered as per pageable.sort
index	Map of id to content item

IndexablePage

An IndexablePage is a special case of Page, it internally stores its data in the same format as a ArrayPage but allows the client some level of control over the response structure. Upon serialization (i.e. invoking toJSON()) if the pageable.indexed value is set to true, the result will be serialized as an IndexedPage (else as an ArrayPage). In order to support this automatic conversion, the underlying content items must each contain an id property.

Output Format

Non-Indexed

GET /people?page=2&size=2&sort=firstname,lastname:desc&indexed=false

{
  "number": 2,
  "size": 2,
  "sort": [
    {
      "direction": "asc",
      "property": "firstname"
    },
    {
      "direction": "lastname",
      "property": "desc"
    }
  ],
  "totalElements": 18,
  "totalPages": 9,
  "first": false,
  "last": false,
  "indexed": false,
  "content": [
    {
      "id": 202,
      "firstName": "Bob",
      "lastName": "Smith"
    },
    {
      "id": 200,
      "firstName": "Bob",
      "lastName": "Jones"
    }
  ],
  "numberOfElements": 2
}

Indexed

GET /people?page=2&size=2&sort=firstname,lastname:desc&indexed=true

{
  "number": 2,
  "size": 2,
  "sort": [
    {
      "direction": "desc",
      "property": "id"
    },
    {
      "direction": "asc",
      "property": "createdTimestamp"
    }
  ],
  "totalElements": 18,
  "totalPages": 9,
  "first": false,
  "last": false,
  "ids": [
    202,
    200
  ],
  "index": {
    "200": {
      "id": 200,
      "firstName": "Frank",
      "lastName": "Jones"
    },
    "202": {
      "id": 202,
      "firstName": "Bob",
      "lastName": "Jones"
    }
  },
  "numberOfElements": 2
}

Getting Started

Installation

npm

npm install @hallysonh/koa-pageable

yarn

yarn add @hallysonh/koa-pageable

Requirements

Requires node >= 8.2, as koa-pageable makes use of async/await. Flow bindings are also provided. Note: The following examples includes optional flow type annotations for clarity.

koa-pageable is a convenient library for managing conversion of user intent (via request parameters) into a Pageable object, but it is still your responsibility to implement that intention when accessing data. You are responsible for ensuring that your data access tier properly implements the pagination and/or sorting, and for creating the Page instances to be returned. The exact approach for doing so will differ based on your chose Data Access framework.

Examples

Router

import { Pageable, IndexedPage, paginate } from '@hallysonh/koa-pageable';
import Koa from 'koa';

var app = new Koa();
app.use(paginate);

app.use(async ctx => {
  // the pageable created from query parameters will be stored in ctx.state.pageable
  const pageable: Pageable = ctx.state.pageable;
  // pass the pageable down into any service and data access tiers, and use its properties to retrieve the appropriate data and return it as a Page
  const result: IndexedPage<Person> = service.getData(pageable);
});

Data Access

Example of using pageable as input to a query, and Page as the response type. This example is based on Objection but should be translatable to any data access / ORM framework.

import { IndexablePage, Pageable, Sort, } from '@hallysonh/koa-pageable';
import type { QueryBuilder } from 'objection';

function getData(pageable: Pageable): IndexablePage<Foo> {
  const pageNumber = pageable.page;
  const pageSize = pageable.size;
  const sort: Sort  = pageable.sort;

  const queryBuilder: QueryBuilder = Person.query().where('age', '>', 21).page(pageNumber, pageSize);

  //If there is a sort, add each order element to the query's `orderBy`
  if (sort) {
    sort.forEach((property, direction) => queryBuilder.orderBy(property, direction));
  }
  const result = await query.execute();

  return new IndexablePage(result.results, result.total, pageable);
}

API Documentation

Access the documentation here