Tuesday, October 21, 2008

A Brief Pyjamas + Django Tutorial

Update: (June 19, 2009) Since the writing of this post, Pyjamas has been updated and the below code no longer works, though the principles discussed are still valid. The example code is now being maintained in the pyjamas Sourceforge repo, located here.


Intro:


Django is a web framework written in Python. Pyjamas is a Python port of the google web toolkit (written in Java). Pyjamas can be used with Django to create web applications.

In terms of an MVC framework, Django acts as the Model and Pyjamas acts as the Views and Controller.

The "Todo List" Application:

In this brief tutorial, we will create a very simple todo list. The primary purpose of this tutorial is to briefly demonstrate how to serve data with Django, how to create and display widgets with Pyjamas, and how to handle user events with Pyjamas.

Prerequesits:

Here is the software that is needed:
This tutorial will not go into how to install each of these components, nor their basic usage. Hopefully, some of them can be downloaded as packages for your linux distribution. One reader recommended that you have a fairly recent Django version. > 1.0 should work.

The Code:

pyjsDemo/urls.py:
from django.conf.urls.defaults import *
from django.conf import settings

urlpatterns = patterns('',
(r'^services/$', 'todo.views.service'),
(r'^site_media/(?P.*)$', 'django.views.static.serve',
{'document_root': settings.STATIC}),
)

pyjsDemo/settings.py


# ADD THIS
import os
STATIC = str(os.path.join(os.path.dirname(__file__), 'media').replace('\\','/'))

# MODIFY THIS
DATABASE_ENGINE = 'mysql' # 'postgresql_psycopg2', 'postgresql', 'mysql', 'sqlite3' or 'oracle'.
DATABASE_NAME = 'todo' # Or path to database file if using sqlite3.
DATABASE_USER = 'todo' # Not used with sqlite3.
DATABASE_PASSWORD = '' # Not used with sqlite3.
DATABASE_HOST = '' # Set to empty string for localhost. Not used with sqlite3.
DATABASE_PORT = '' # Set to empty string for default. Not used with sqlite3.

# MODIFY THIS
INSTALLED_APPS = (
'pyjsDemo.todo',
)

pyjsDemo/todo/models.py:

from django.db import models

class Todo(models.Model):
task = models.CharField(max_length=30)

def __unicode__(self):
return str(self.task)


pyjsDemo/todo/views.py:


from django.pimentech.network import *
from todo.models import Todo

service = JSONRPCService()

@jsonremote(service)
def getTasks (request):
return [(str(task),task.id) for task in Todo.objects.all()]


@jsonremote(service)
def addTask (request, taskFromJson):
t = Todo()
t.task = taskFromJson
t.save()
return getTasks(request)

@jsonremote(service)
def deleteTask (request,idFromJson):
t = Todo.objects.get(id=idFromJson)
t.delete()
return getTasks(request)


pyjsDemo/media/TodoApp.html:



See the download for this. It's short, but I can't figure out how to paste html into my blog. I'm lazy.



pyjsDemo/media/TodoApp.py:


from ui import Label, RootPanel, VerticalPanel, TextBox, KeyboardListener, ListBox
from JSONService import JSONProxy

class TodoApp:
def onModuleLoad(self):
self.remote = DataService()
panel = VerticalPanel()

self.todoTextBox = TextBox()
self.todoTextBox.addKeyboardListener(self)

self.todoList = ListBox()
self.todoList.setVisibleItemCount(7)
self.todoList.setWidth("200px")
self.todoList.addClickListener(self)

panel.add(Label("Add New Todo:"))
panel.add(self.todoTextBox)
panel.add(Label("Click to Remove:"))
panel.add(self.todoList)
RootPanel().add(panel)


def onKeyUp(self, sender, keyCode, modifiers):
pass

def onKeyDown(self, sender, keyCode, modifiers):
pass

def onKeyPress(self, sender, keyCode, modifiers):
"""
This functon handles the onKeyPress event, and will add the item in the text box to the list when the user presses the enter key. In the future, this method will also handle the auto complete feature.
"""
if keyCode == KeyboardListener.KEY_ENTER and sender == self.todoTextBox:
id = self.remote.addTask(sender.getText(),self)
sender.setText("")
if id<0: id =" self.remote.deleteTask(sender.getValue(sender.getSelectedIndex()),self)" method ="=" method ="=" method ="=">

pyjsDemo/media/build.sh

python ~/python/pyjamas-0.3/builder/build.py TodoApp.py



A very brief walk through of how to get this running:

Extract the demo:
  • tar -xvvzf pyjamasDjango.tar.gz
Create the db:
  • mysql -u root
  • > CREATE DATABASE todo;
  • > grant all privilages to todo.* to 'todo'@'localhost'; (or possibly > grant all on todo.* to 'todo'@'localhost';)
  • > exit;
Create the tables:
  • cd pyjsDemo
  • python manage.py syncdb
Build the javascript:
  • vim media/build.sh
  • (edit this so that it points to the build.py of pyjamas)
  • media/build.sh
Run the server:
  • python manage.py runserver
Test it out:
  • In your browser, goto: http://127.0.0.1:8000/site_media/output/TodoApp.html

Here are the demo source files:

11 comments:

mauro said...

I tried the demo
the db gets updated but the list is not shown on the page...
any idea?

OlsenUpdate said...

thank you so much for this great enlightment. I don't know what i'd do without you bro!

Jeff Bauer said...

Agree with mauro. New items get added to the database, but do not appear on the task list. onRemoteReponse is not invoked.

Another suggestion for this example would be to demo it with sqlite, rather than MySQL.

Dr. Mobeus said...

Works perfectly for me, using Pyjamas 0.4 and mySQL 5.1 and Django 1.02. I'm on WinXp SP3.
Just to update matters, if you are also on mySQl 5.1, the syntax has changed, so that you have to do:
CREATE USER todo.localhost
before granting rights. minor point, but it might stub a newbie :-)

I'm wondering if it's possible to use Pyjamas to interact with Dojo (or better still, 'wrap' dijit controls)... At the very least - as a stop gap - I might try using dojo controls on a DJango template, and the write the functions that are triggered by user events (e.g. clicking on a button) in pyjamas.

Amund Tveit said...

Nice posting.

Wrote a similar one covering pyjs + appengine - http://amundblog.blogspot.com/2008/12/ajax-with-python-combining-pyjs-and.html

funkazio said...

Thanks!Interesting!

@ mauro and Jeff Bauer

The task list seems not to be updated because a Javascript error is fired when you don't have the "FireBug" plugin installed (all the "console.something()" instructions only work with this plugin). After you install that, the example works (at least for me) using mysql or sqlite3. However the task list is loaded only when you insert a task, and not at startup. (ok for me then, using. WinXPsp3, Python2.6, Django 1.1 pre-alpha SVN-9645, pyjamas-0.4, libcommonDjango).

Soulburner said...

To get the todolist populating on page load i added
"self.remote.getTasks(self)"
to the end of the onmoduleload function

was playing around with using this in an existing web app and i found you can use django templating to dynamically change the content and src directory in the base html file

simak said...

Hello. Nice source of info about pyjamas and Django, but I had some problems here: A blank page. Any I deas on how to debug it? Any log I could pay attention to?

Giancasa said...

when i try the tutorial with pyjamas 0.5 i get this error :"Exception: file not found: JSONService.py" after buld.sh. to "upgrade" the tutorial for pyjamas 0.5sp1 we must change the import in TodoApp.py
in
from pyjamas.ui import Label, RootPanel, VerticalPanel, TextBox, KeyboardListener, ListBox
from pyjamas.JSONService import JSONProxy

hope this help.

Giancasa

Raketemensch said...
This comment has been removed by the author.
Raketemensch said...

The build.sh wasn't working for me for some reason, so I just manually called "pyjsbuild ToDoApp" and moved on to launching the server.

The app bombs for me though. Trying to enter text throws:

JavaScript Error: object is undefined at line number 2050. Please inform webmaster.

Clicking the (empty) task list throws:

JavaScript Error: elem is null at line number 4346. Please inform webmaster.

I have tried installing FireBug as mentioned above, but still no joy. I'm running Firefox 3.0.13 on OS Leopard.

Pyjamas