REST Api

flask-peewee comes with some tools for exposing your project’s models via a RESTful API. There are several components to the rest module, but the basic setup is to create an instance of RestAPI and then register your project’s models with subclasses of RestResource.

Each RestResource you expose via the API will support, by default, the following:

  • /api/<model name>/ – GET and POST requests
  • /api/<model name>/<primary key>/ – GET, PUT and DELETE requests

Also, you can filter results by columns on the model using django-style syntax, for example:

  • /api/blog/?name=Some%20Blog
  • /api/blog/?author__username=some_blogger

Getting started with the API

In this documentation we’ll start with a very simple API and build it out. The complete version of this API is included in the example-app, so feel free to refer there.

The project will be a simple ‘twitter-like’ app where users can post short messages and “follow” other users.

Note

If you’re using apache with mod_wsgi and would like to use any of the auth backends that use basic auth, you will need to add the following directive: WSGIPassAuthorization On

Project models

There are three main models - User, Relationship and Message - which we will expose via the API. Here is a truncated version of what they look like:

from flask_peewee.auth import BaseUser

class User(db.Model, BaseUser):
    username = CharField()
    password = CharField()
    email = CharField()
    join_date = DateTimeField(default=datetime.datetime.now)
    active = BooleanField(default=True)
    admin = BooleanField(default=False)

class Relationship(db.Model):
    from_user = ForeignKeyField(User, related_name='relationships')
    to_user = ForeignKeyField(User, related_name='related_to')

class Message(db.Model):
    user = ForeignKeyField(User)
    content = TextField()
    pub_date = DateTimeField(default=datetime.datetime.now)

Creating a RestAPI

The RestAPI acts as a container for the various RestResource objects we will expose. By default it binds all resources to /api/<model-name>/.

Here we’ll create a simple api and register our models:

from flask_peewee.rest import RestAPI

from app import app # our project's Flask app

# instantiate our api wrapper
api = RestAPI(app)

# register our models so they are exposed via /api/<model>/
api.register(User)
api.register(Relationship)
api.register(Message)

# configure the urls
api.setup()

Now if we hit our project at /api/message/ we should get something like the following:

{
  "meta": {
    "model": "message",
    "next": "",
    "page": 1,
    "previous": ""
  },
  "objects": [
    {
      "content": "flask and peewee, together at last!",
      "pub_date": "2011-09-16 18:36:15",
      "user_id": 1,
      "id": 1
    },
    {
      "content": "Hey, I'm just some user",
      "pub_date": "2011-09-16 18:46:59",
      "user_id": 2,
      "id": 2
    }
  ]
}

Say we’re interested in the first message, we can hit /api/message/1/ to view just the details on that object:

{
  content: "flask and peewee, together at last!"
  pub_date: "2011-09-16 18:36:15"
  user_id: 1
  id: 1
}

Customizing what is returned

If you access the User API endpoint, we quickly notice a problem:

$ curl http://127.0.0.1:5000/api/user/

{
  "meta": {
    "model": "user",
    "next": "",
    "page": 1,
    "previous": ""
  },
  "objects": [
    {
      "username": "admin",
      "admin": true,
      "email": "",
      "join_date": "2011-09-16 18:34:49",
      "active": true,
      "password": "d033e22ae348aeb5660fc2140aec35850c4da997",
      "id": 1
    },
    {
      "username": "coleifer",
      "admin": false,
      "email": "coleifer@gmail.com",
      "join_date": "2011-09-16 18:35:56",
      "active": true,
      "password": "a94a8fe5ccb19ba61c4c0873d391e987982fbbd3",
      "id": 2
    }
  ]
}

Passwords and email addresses are being exposed. In order to exclude these fields from serialization, subclass RestResource:

from flask_peewee.rest import RestAPI, RestResource

from app import app # our project's Flask app

# instantiate our api wrapper
api = RestAPI(app)

# create a special resource for users that excludes email and password
class UserResource(RestResource):
    exclude = ('password', 'email',)

# register our models so they are exposed via /api/<model>/
api.register(User, UserResource) # specify the UserResource
api.register(Relationship)
api.register(Message)

Now emails and passwords are no longer returned by the API.

Allowing users to post objects

What if we want to create new messages via the Api? Or modify/delete existing messages?

$ curl -i -d '' http://127.0.0.1:5000/api/message/

HTTP/1.0 401 UNAUTHORIZED
WWW-Authenticate: Basic realm="Login Required"
Content-Type: text/html; charset=utf-8
Content-Length: 21
Server: Werkzeug/0.8-dev Python/2.6.6
Date: Thu, 22 Sep 2011 16:14:21 GMT

Authentication failed

The authentication failed because the default authentication mechanism only allows read-only access.

In order to allow users to create messages via the API, we need to use a subclass of Authentication that allows POST requests. We also want to ensure that the requesting user is a member of the site.

For this we will use the UserAuthentication class as the default auth mechanism.

from auth import auth # import the Auth object used by our project

from flask_peewee.rest import RestAPI, RestResource, UserAuthentication

# create an instance of UserAuthentication
user_auth = UserAuthentication(auth)

# instantiate our api wrapper, specifying user_auth as the default
api = RestAPI(app, default_auth=user_auth)

# create a special resource for users that excludes email and password
class UserResource(RestResource):
    exclude = ('password', 'email',)

# register our models so they are exposed via /api/<model>/
api.register(User, UserResource) # specify the UserResource
api.register(Relationship)
api.register(Message)

# configure the urls
api.setup()

Now we should be able to POST new messages.

import json
import httplib2

sock = httplib2.Http()
sock.add_credentials('admin', 'admin') # use basic auth

message = {'user_id': 1, 'content': 'hello api'}
msg_json = json.dumps(message)

headers, resp = sock.request('http://localhost:5000/api/message/', 'POST', body=msg_json)

response = json.loads(resp)

The response object will look something like this:

{
  'content': 'hello api',
  'user_id': 1,
  'pub_date': '2011-09-22 11:25:02',
  'id': 3
}

There is a problem with this, however. Notice how the user_id was passed in with the POST data? This effectively will let a user post a message as another user. It also means a user can use PUT requests to modify another user’s message:

# continued from above script
update = {'content': 'haxed you, bro'}
update_json = json.dumps(update)

headers, resp = sock.request('http://127.0.0.1:5000/api/message/2/', 'PUT', body=update_json)

response = json.loads(resp)

The response will look like this:

{
  'content': 'haxed you, bro',
  'pub_date': '2011-09-16 18:36:15',
  'user_id': 2,
  'id': 2
}

This is a problem – we need a way of ensuring that users can only edit their own messages. Furthermore, when they create messages we need to make sure the message is assigned to them.

Restricting API access on a per-model basis

flask-peewee comes with a special subclass of RestResource that restricts POST/PUT/DELETE requests to prevent users from modifying another user’s content.

from flask_peewee.rest import RestrictOwnerResource


class MessageResource(RestrictOwnerResource):
    owner_field = 'user'

api.register(Message, MessageResource)

Now, if we try and modify the message, we get a 403 Forbidden:

headers, resp = sock.request('http://127.0.0.1:5000/api/message/2/', 'PUT', body=update_json)
print headers['status']

# prints 403

It is fine to modify our own message, though (message with id=1):

headers, resp = sock.request('http://127.0.0.1:5000/api/message/1/', 'PUT', body=update_json)
print headers['status']

# prints 200

Under-the-hood, the implementation of the RestrictOwnerResource is pretty simple.

  • PUT / DELETE – verify the authenticated user is the owner of the object
  • POST – assign the authenticated user as the owner of the new object

Locking down a resource

Suppose we want to restrict normal users from modifying User resources. For this we can use a special subclass of UserAuthentication that restricts access to administrators:

from flask_peewee.rest import AdminAuthentication

# instantiate our user-based auth
user_auth = UserAuthentication(auth)

# instantiate admin-only auth
admin_auth = AdminAuthentication(auth)

# instantiate our api wrapper, specifying user_auth as the default
api = RestAPI(app, default_auth=user_auth)

# register the UserResource with admin auth
api.register(User, UserResource, auth=admin_auth)

Filtering records and querying

A REST Api is not very useful if it cannot be queried in a meaningful fashion. To this end, the flask-peewee RestResource objects support “django-style” filtering:

$ curl http://127.0.0.1:5000/api/message/?user=2

This call will return only messages by the User with id=2:

{
  "meta": {
    "model": "message",
    "next": "",
    "page": 1,
    "previous": ""
  },
  "objects": [
    {
      "content": "haxed you, bro",
      "pub_date": "2011-09-16 18:36:15",
      "user_id": 2,
      "id": 2
    }
  ]
}

Joins can be traversed using the django double-underscore notation:

$ curl http://127.0.0.1:5000/api/message/?user__username=admin
{
  "meta": {
    "model": "message",
    "next": "",
    "page": 1,
    "previous": ""
  },
  "objects": [
    {
      "content": "flask and peewee, together at last!",
      "pub_date": "2011-09-16 18:36:15",
      "user_id": 1,
      "id": 1
    },
    {
      "content": "hello api",
      "pub_date": "2011-09-22 11:25:02",
      "user_id": 1,
      "id": 3
    }
  ]
}

It is also supported to use different comparison operators with the same double-underscore notation:

$ curl http://127.0.0.1:5000/api/user/?user__lt=2
{
  "meta": {
    "model": "user",
    "next": "",
    "page": 1,
    "previous": ""
    },
"objects": [{
    "username": "admin",
    "admin": true,
    "email": "admin@admin",
    "active": true,
    "password": "214de$25",
    "id": 1
    }]
}
Valid Comparison Operators are:
‘eq’, ‘lt’, ‘lte’, ‘gt’, ‘gte’, ‘ne’, ‘in’, ‘is’, ‘like’, ‘ilike’

Sorting results

Results can be sorted by specifying an ordering as a GET argument. The ordering must be a column on the model.

/api/messages/?ordering=pub_date

If you would like to order objects “descending”, place a “-” (hyphen character) before the column name:

/api/messages/?ordering=-pub_date

Limiting results and pagination

By default, resources are paginated 20 per-page. If you want to return less, you can specify a limit in the querystring.

/api/messages/?limit=2

In the “meta” section of the response, URIs for the “next” and “previous” sets of results are available:

meta: {
  model: "message"
  next: "/api/message/?limit=1&page=3"
  page: 2
  previous: "/api/message/?limit=1&page=1"
}