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 @panderalabs/koa-pageable
yarn
yarn add @panderalabs/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
// @flow
import { Pageable, IndexedPage, paginate } from '@panderalabs/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.
// @flow
import { IndexablePage, Pageable, Sort, } from '@panderalabs/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);
}