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= URL Conventions =
= URL Conventions =


You can get a bit more mileage from having separate lists and instances of your widgets.
These are the recommended conventions for [http://bitworking.org/news/How_to_create_a_REST_Protocol RESTful] [http://www.softiesonrails.com/2007/4/10/rest-101-part-3-just-call-me-the-repo-man URLs], based on work pioneered by [http://topfunky.com/clients/peepcode/REST-cheatsheet.pdf Ruby on Rails], which again is closely modelled over [http://www.ietf.org/rfc/rfc5023.txt Atompub] . Following these conventions for both HTTP method names and URL construction will allow your application to be consumed by ActiveResource,  Jester, and other RESTful clients. Note that Rails 1.x used ";edit" and ";new" in place of the simpler "/edit" and "/new" recommended going forward.


There is nothing that says you must organise resources hierarchically,
== Methods ==
although many people prefer to do so. There are advantages to separating
One of the key aspects of REST is using the [http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html HTTP Verbs] to implement the standard Create-Retrieve-Update-Delete ([http://en.wikipedia.org/wiki/Create%2C_read%2C_update_and_delete CRUD]) database semantics. The primary ones are:
your containment hierarchies from your components. It makes it trivial
to add new containers and the containers can accept search parameters.


== Example URLs ==
;POST:'''C'''reate a resource within a given collection
;GET:'''R'''etrieve a resource
;PUT:'''U'''pdate a resource
;DELETE:'''D'''elete a resource


You could organise your URIs like this:
Most browsers do not currently support PUT and DELETE (HTML forms only allow "get" and "post", links are always "get").  The other methods can be emulated by providing a "method" parameter with a value of "PUT" and "DELETE", respectively.


* The second widget
== Routing ==
http://example.org/widget/2
The principal unit of operation is the "collection", which typically corresponds to a database table or (in Rails) an ActiveRecord class.
For a collection named "people", the primary routes would be:


* A form describing how to create a widget
=== Operate on the Collection ===
http://example.org/widget
;GET /people: return a list of all records
;GET /people/new: return a form for creating a new record
;POST /people: submit fields for creating a new record


* The list of the first N (say N=25) widgets
=== Operate on a Record ===
http://example.org/widgets


* The list of the next N widgets starting at 26
;GET /people/1: return the first record
http://example.org/widgets/26
;DELETE /people/1: destroy the first record
;POST /people/1?_method=DELETE: alias for DELETE, to compensate for browser limitations


== Example Actions ==
;GET /people/1/edit: return a form to edit the first record
;PUT /people/1: submit fields for updating the first record
;POST /people/1?_method=PUT: alias for PUT, to compensate for browser limitations


Then consider a sequence of hypertext style actions:
=== Follow a Relationship ===


* Retrieve a list of widgets
;GET /people/1/phones: return the collection of phone numbers associated with the first person
GET http://example.org/widgets
;GET /people/1/phones/23: return the phone number with id #23 associated with the first person
;GET /people/1/phones/new: return a form for creating a new phone number for the first person
;POST /people/1/phones/: submit fields for creating a new phone number for the first person


* Retrieve details of the second one
=== Invoke Custom Actions ===
  GET  http://example.org/widget/2
It isn't always possible to map ''everything'' into CRUD. Thus, there is also a syntax for specifying custom actions:
;POST /people/1/promote: run the "promote" action against the first record
These should be used sparingly, as they are unlikely to be supported by most clients.


* Replace some of the details
== File Formats ==
POST  http://example.org/widget/2


* Retrieve a form (resource parameter decription)
Data types are extremely important in REST.  While it is ideal to specify the appropriate [http://en.wikipedia.org/wiki/Internet_media_type MIME type] as an HTTP header, developers are encouraged to follow Rails in allowing extension-based typing, e.g.:
* or whatever you want to call it, for creating widgets
GET  http://example.org/widget


* Create a new widget
=== HTML ===
POST  http://example.org/widget
;GET /people/1: return the first record in HTML format
<= LOCATION:  //example.org/widget/123
;GET /people/1.html: return the first record in HTML format
=== XML ===
;GET /people/1.xml: return the first record in [http://en.wikipedia.org/wiki/XML XML] format
=== JSON ===
;GET /people/1.json: return the first record in [http://en.wikipedia.org/wiki/JSON JSON] format


* Get the new widget
While the JSON mapping should be trivially obvious, the best practice for XML is to:
GET  http://example.org/widget/123
# use the column name as the element name
# include an appropriate "type" field


* Delete the Widget
See the [http://developer.37signals.com/highrise/reference.shtml Highrise reference] for an example of how this works in practice.
DELETE  http://example.org/widget/123


== Notes ==
== Response Codes ==  
Another important aspect of REST is returning the appropriate [http://en.wikipedia.org/wiki/List_of_HTTP_status_codes HTTP Response Codes]. Some common ones are:
=== Successful ===
;200 OK: The request has succeeded.
;201 Created: The request has been fulfilled and resulted in a new resource being created. The newly created resource can be referenced by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header field.
;204 No Content: The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation.
=== Redirection ===
;303 See Other:The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource.


This organisation is similar to that of the rest-discuss
=== Client Error ===
html interface. But you cannot use PUT, POST and DELETE in
;400 Bad Request: The request could not be understood by the server due to malformed syntax.
that interface.
;401 Unauthorized: The request requires user authentication. The response MUST include a WWW-Authenticate header field ([http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html 14.47]) containing a challenge applicable to the requested resource.
;404 Not Found: The requested resource could not be found([http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.5 section 10.4.5]).
;405 Method Not Allowed: The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response MUST include an Allow header containing a list of valid methods for the requested resource.
; 422 Unprocessable Entity: The server understands the media type of the request entity, but was unable to process the contained instructions.


Using the  http://example.org/widget URI for creating new widgets is
= Examples in the Wild =
similar to the Prototype design pattern while still adhering to the
== Ruby ==
expected behaviour of a POST, ie. create a subordinate resource.
* [http://guides.rubyonrails.org/routing_outside_in.html Ruby on Rails]
* [http://developer.37signals.com/highrise/ Highrise]
 
== PHP ==
 
* [http://github.com/shuber/restful_rails/tree/master RestfulRails] An extendable PHP library to communicate with RESTful rails applications
 
== Perl ==
 
* [http://dev.catalyst.perl.org/wiki/crud/crud_and_rest Catalyst CRUD and REST]
 
== Java ==
* [http://weblogs.java.net/blog/bleonard/archive/2007/08/rails_to_java_v.html Java]
== Python ==
* [http://routes.groovie.org/manual.html#restful-services  Python Routes]
* [http://pylonshq.com/docs/module-pylons.decorators.rest.html Pylons REST Decorators]
 
== JavaScript ==
* [http://giantrobots.thoughtbot.com/2007/4/2/jester-javascriptian-rest Jester] (JavaScript)
* [http://code.google.com/p/dom-resource/ DOM-Resource] (JavaScript)
* ....

Latest revision as of 12:28, 7 May 2009

URL Conventions

These are the recommended conventions for RESTful URLs, based on work pioneered by Ruby on Rails, which again is closely modelled over Atompub . Following these conventions for both HTTP method names and URL construction will allow your application to be consumed by ActiveResource, Jester, and other RESTful clients. Note that Rails 1.x used ";edit" and ";new" in place of the simpler "/edit" and "/new" recommended going forward.

Methods

One of the key aspects of REST is using the HTTP Verbs to implement the standard Create-Retrieve-Update-Delete (CRUD) database semantics. The primary ones are:

POST
Create a resource within a given collection
GET
Retrieve a resource
PUT
Update a resource
DELETE
Delete a resource

Most browsers do not currently support PUT and DELETE (HTML forms only allow "get" and "post", links are always "get"). The other methods can be emulated by providing a "method" parameter with a value of "PUT" and "DELETE", respectively.

Routing

The principal unit of operation is the "collection", which typically corresponds to a database table or (in Rails) an ActiveRecord class. For a collection named "people", the primary routes would be:

Operate on the Collection

GET /people
return a list of all records
GET /people/new
return a form for creating a new record
POST /people
submit fields for creating a new record

Operate on a Record

GET /people/1
return the first record
DELETE /people/1
destroy the first record
POST /people/1?_method=DELETE
alias for DELETE, to compensate for browser limitations
GET /people/1/edit
return a form to edit the first record
PUT /people/1
submit fields for updating the first record
POST /people/1?_method=PUT
alias for PUT, to compensate for browser limitations

Follow a Relationship

GET /people/1/phones
return the collection of phone numbers associated with the first person
GET /people/1/phones/23
return the phone number with id #23 associated with the first person
GET /people/1/phones/new
return a form for creating a new phone number for the first person
POST /people/1/phones/
submit fields for creating a new phone number for the first person

Invoke Custom Actions

It isn't always possible to map everything into CRUD. Thus, there is also a syntax for specifying custom actions:

POST /people/1/promote
run the "promote" action against the first record

These should be used sparingly, as they are unlikely to be supported by most clients.

File Formats

Data types are extremely important in REST. While it is ideal to specify the appropriate MIME type as an HTTP header, developers are encouraged to follow Rails in allowing extension-based typing, e.g.:

HTML

GET /people/1
return the first record in HTML format
GET /people/1.html
return the first record in HTML format

XML

GET /people/1.xml
return the first record in XML format

JSON

GET /people/1.json
return the first record in JSON format

While the JSON mapping should be trivially obvious, the best practice for XML is to:

  1. use the column name as the element name
  2. include an appropriate "type" field

See the Highrise reference for an example of how this works in practice.

Response Codes

Another important aspect of REST is returning the appropriate HTTP Response Codes. Some common ones are:

Successful

200 OK
The request has succeeded.
201 Created
The request has been fulfilled and resulted in a new resource being created. The newly created resource can be referenced by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header field.
204 No Content
The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation.

Redirection

303 See Other
The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource.

Client Error

400 Bad Request
The request could not be understood by the server due to malformed syntax.
401 Unauthorized
The request requires user authentication. The response MUST include a WWW-Authenticate header field (14.47) containing a challenge applicable to the requested resource.
404 Not Found
The requested resource could not be found(section 10.4.5).
405 Method Not Allowed
The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response MUST include an Allow header containing a list of valid methods for the requested resource.
422 Unprocessable Entity
The server understands the media type of the request entity, but was unable to process the contained instructions.

Examples in the Wild

Ruby

PHP

  • RestfulRails An extendable PHP library to communicate with RESTful rails applications

Perl

Java

Python

JavaScript

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