@panderalabs/koa-pageable
v1.0.1
Published
Koa Pagination framework inspired by Spring Data's Pagination approach.
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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 pagesort
| 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);
}
API Documentation
https://panderalabs.github.io/koa-pageable/