django-banjo 0.0.1

A simplified wrapper over django for beginners.

Banjo

This is a django wrapper which provides a simplified subset of django's functionality. The intended usage is that students will only interact with banjo, not django. All the django documentation can be used for reference, with the caveat that many of the options are not available.

Needs

The purpose of Banjo is to introduce databases as a persistence layer behind an API server, while abstracting away details for which students are not yet ready while creating as few misconceptions as possible.

Banjo should be thought of as scaffolding; when they are ready, students should be able to seamlessly transition to django.

Specific concepts which we target for simplification include:

• Simplify DB schema: A severly-limited subset of field types is provided. There are no foreign key relations or field options. Field names correspond to familiar Python types. All fields have default values. Within these constraints, django's full ORM is available.

• Simplify filesystem layout: Only two files are required: models.py and views.py. View-URL binding is handled by decorators, as in flask, and all URLs are static (there are no placeholders and no params are passed to the view). Additionally, db.sqlite3 will be created when the server runs.

• Simplify management commands: There is a single command, banjo, which effectively runs django's makemigrations, migrate, and runserver in sequence.

• Simplify request/response lifecycle: View functions receive a status code and a dict of POST params. View functions must return a dict. Http errors are provided as exceptions, which simplifies control flow. Models have helper methods, from_dict and to_dict.

Usage

To write a Banjo app, create a folder called app, define models in models.py and define views in views.py. Here's a simple example.

First, we define our models. Banjo provides four field types:

• BooleanField (True, False)
• IntegerField (1, -102)
• FloatField (0.045, 11.5)
• StringField ("alligator", "hazelnut")

app/models.py

from banjo.models import Model, StringField

class Animal(Model):
    name = StringField()
    sound = StringField()

Next we define our views. Each view is a function which receives a dict (called params in the example below) and which must return a dict. Use the banjo.urls.route_get and banjo.urls.route_post decorators to route URLs to your view functions.

app/views.py

from banjo.urls import route_get, route_post
from models import Animal

@route('newanimal')
def add_animal(params):
    animal = Animal.from_dict(params)
    animal.save()
    return animal.to_dict()

@route('listen')
def list_animal_sounds(params):
    sounds = []
    for animal in Animal.objects.all():
        sounds.append('{} says {}'.format(a.name, a.sound))     
    return {'sounds': sounds}

Now you can run banjo from the directory containing these files and the server will start. Use the --port command to serve from a custom port; the default is 5000.

Here is an example of interacting with this app using the httpie command-line utility:

$ http localhost:5000/add name=elehpant sound=pffffftttttt

{ 
  "name": "elephant",
  "sound": "pffffftttttt"
}

$ http localhost:5000/add name=squirrel sound=chcheee

{ 
  "name": "squirrel",
  "sound": "chcheee"
}

$ http localhost:5000/listen

{
  "sounds": [
    "elephant says pffffftttttt",
    "squirrel says chcheee"
  ]
}

HTTP errors

If something goes wrong and it's the client's fault, you can raise an error. For example:

from banjo.http import NotAllowed

@route_get('error')
def error(params):
    raise NotAllowed("I said no.")

The following errors are available in banjo.http:

• BadRequest (400)
• Forbidden (403)
• NotFound (404)
• NotAllowed (405)
• ImATeapot (418)

Shell

You can also interact with your app's models from a Python shell. Just pass the --shell argument to banjo:

$ banjo --shell
> Animal.objects.count()
2