Python Blog: June 2013

Create a project

If this is your first time using Django, you’ll have to take care of some initial setup. Namely, you’ll need to auto-generate some code that establishes a Django project – a collection of settings for an instance of Django, including database configuration, Django-specific options and application-specific settings.

From the command line, cd into a directory where you’d like to store your code, then run the following command:

django-admin.py startproject demo_project

This will create a mysite directory in your current directory. Let’s look at what startproject created:

demo_project/
    manage.py
    demo_project/
        __init__.py
        settings.py
        urls.py
        wsgi.py

Description about these file:

The outer demo_project/ directory is just a container for your project. Its name doesn’t matter to Django; you can rename it to anything you like.
manage.py: A command-line utility that lets you interact with this Django project in various ways. You can read all the details about manage.py in django-admin.py and manage.py.
The inner demo_project/ directory is the actual Python package for your project. Its name is the Python package name you’ll need to use to import anything inside it (e.g. import demo_project.settings).
demo_project/__init__.py: An empty file that tells Python that this directory should be considered a Python package. (Read more about packages in the official Python docs if you’re a Python beginner.)
demo_project/settings.py: Settings/configuration for this Django project. Django settings will tell you all about how settings work.
demo_project/urls.py: The URL declarations for this Django project; a “table of contents” of your Django-powered site. You can read more about URLs in URL dispatcher.
demo_project/wsgi.py: An entry-point for WSGI-compatible web servers to serve your project. See How to deploy with WSGI for more details. this is Apache file.

Now we want to confirm that it will work or not so go to this directory by command up to demo_project/
By default, the runserver command starts the development server on the internal IP at port 8000.

C:\Python27\project\demo_project>python manage.py runserver

or this command starts the server on port 1111:

C:\Python27\project\demo_project>python manage.py runserver 1111

or If you want to change the server’s IP, pass it along with the port. So to listen on all public IPs (useful if you want to show off your work on other computers), use:

C:\Python27\project\demo_project>python manage.py runserver 192.168.*.*:1111

* means your IP address and if you don't know your ip then open your command prompt and type "ipconfig/all" And check your ip and put above line and run it. you will get below result.

Validating models...

0 errors found
June 02, 2013 - 15:50:53
Django version 1.6, using settings 'mysite.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.

Now that the server’s running, visit http://127.0.0.1:8000/ with your Web browser for window and for linux run as http://localhost:1111 . You’ll see a “Welcome to Django” page, in pleasant, light-blue pastel. It worked!

Database setup

Now, edit demo_project/settings.py. It’s a normal Python module with module-level variables representing Django settings.

In your settings.py you will see setting like this

DATABASE_ENGINE = 'django.db.backends.mysql'
DATABASE_NAME = 'demo'     # Or path to database file if using sqlite3.
DATABASE_USER = 'root'             # Not used with sqlite3.
DATABASE_PASSWORD = ''             # Not used with sqlite3.
DATABASE_HOST = ''                 # Set to empty string for localhost. Not used with sqlite3.
DATABASE_PORT = '' 

DATABASES = {
    'default': {
        'NAME': DATABASE_NAME,
        'ENGINE': DATABASE_ENGINE,
        'HOST': DATABASE_HOST,
        'USER': DATABASE_USER,
        'PASSWORD': DATABASE_PASSWORD,
    
    }
}

If you wish to use another database, install the appropriate database bindings, and change the following keys in theDATABASES 'default' item to match your database connection settings:

ENGINE – Either 'django.db.backends.sqlite3', 'django.db.backends.postgresql_psycopg2','django.db.backends.mysql', or 'django.db.backends.oracle'. Other backends are also available.
NAME – The name of your database. If you’re using SQLite, the database will be a file on your computer; in that case, NAMEshould be the full absolute path, including filename, of that file. The default value,os.path.join(BASE_DIR, 'db.sqlite3'), will store the file in your project directory.
set TIME_ZONE to your time zone.
set LANGUAGE_CODE to your language.

Also, note the INSTALLED_APPS setting at the top of the file. That holds the names of all Django applications that are activated in this Django instance. Apps can be used in multiple projects, and you can package and distribute them for use by others in their projects.

By default, INSTALLED_APPS contains the following apps, all of which come with Django:

django.contrib.admin – The admin site. You’ll use it in part 2 of this tutorial.
django.contrib.auth – An authentication system.
django.contrib.contenttypes – A framework for content types.
django.contrib.sessions – A session framework.
django.contrib.messages – A messaging framework.
django.contrib.staticfiles – A framework for managing static files.

Now Manually create database in your MYSQL and run this command in your command line like this

C:\Python27\project\demo_project>python manage.py syncdb

The syncdb command looks at the INSTALLED_APPS setting and creates any necessary database tables according to the database settings in your mysite/settings.py file. You’ll see a message for each database table it creates, and you’ll get a prompt asking you if you’d like to create a superuser account for the authentication system. Go ahead and do that.

Creating Apps and models

Projects vs. apps

What’s the difference between a project and an app? An app is a Web application that does something – e.g., a Weblog system, a database of public records or a simple poll app. A project is a collection of configuration and apps for a particular Web site. A project can contain multiple apps. An app can be in multiple projects.

To create your app, make sure you’re in the same directory as manage.py and type this command:

python manage.py startapp polls

That’ll create a directory polls, which is laid out like this:

polls/
    __init__.py
    admin.py
    models.py
    tests.py
    views.py

This directory structure will house the poll application. In our simple poll app, we’ll create two models: Poll and Choice. A Poll has a question and a publication date. A Choice has two fields: the text of the choice and a vote tally. Each Choice is associated with a Poll. These concepts are represented by simple Python classes. Edit the polls/models.py file so it looks like this:

from django.db import models

class Poll(models.Model):
    question = models.CharField(max_length=200)
    pub_date = models.DateTimeField('date published')

class Choice(models.Model):
    poll = models.ForeignKey(Poll)
    choice_text = models.CharField(max_length=200)
    votes = models.IntegerField(default=0)

Notes:

Each field is represented by an instance of a Field class – e.g., CharField for character fields and DateTimeField for datetimes. This tells Django what type of data each field holds.

The name of each Field instance (e.g. question or pub_date) is the field’s name, in machine-friendly format. You’ll use this value in your Python code, and your database will use it as the column name.

You can use an optional first positional argument to a Field to designate a human-readable name. That’s used in a couple of introspective parts of Django, and it doubles as documentation. If this field isn’t provided, Django will use the machine-readable name. In this example, we’ve only defined a human-readable name for Poll.pub_date. For all other fields in this model, the field’s machine-readable name will suffice as its human-readable name.

Some Field classes have required arguments. CharField, for example, requires that you give it a max_length. That’s used not only in the database schema, but in validation, as we’ll soon see.

A Field can also have various optional arguments; in this case, we’ve set the default value of votes to 0.

Finally, note a relationship is defined, using ForeignKey. That tells Django each Choice is related to a single Poll. Django supports all the common database relationships: many-to-ones, many-to-manys and one-to-ones.

Activate this Apps in your project: Edit the mysite/settings.py file again, and change the INSTALLED_APPS setting to include the string 'polls'. So it’ll look like this:

INSTALLED_APPS = (
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'polls',
)

Now Django knows to include the polls app. Let’s run another command:

python manage.py sql polls

You should see something similar to the following (the CREATE TABLE SQL statements for the polls app):

BEGIN;
CREATE TABLE "polls_poll" (
    "id" integer NOT NULL PRIMARY KEY,
    "question" varchar(200) NOT NULL,
    "pub_date" datetime NOT NULL
);
CREATE TABLE "polls_choice" (
    "id" integer NOT NULL PRIMARY KEY,
    "poll_id" integer NOT NULL REFERENCES "polls_poll" ("id"),
    "choice_text" varchar(200) NOT NULL,
    "votes" integer NOT NULL
);
COMMIT;

Now, run syncdb again to create those model tables in your database:

python manage.py syncdb

Important Notes: Playing with the API Now, let’s hop into the interactive Python shell and play around with the free API Django gives you. To invoke the Python shell, use this command:

python manage.py shell


Once you’re in the shell, explore the database API:

How to write Database Query:

first import that table which is present in database.

>>from polls.models import Poll, Choice

>>Table_name.objects.all()

It fetch all values in table means fetch all row of tables.

>>Table_name.objects.get(pk=id)

It fetch single row values in table according to where condition .

>>Table_name.objects.filter(pk=id)

It fetch multiple row values in table according to where condition  .




>>> from polls.models import Poll, Choice   # Import the model classes we just wrote.

# No polls are in the system yet.
>>> Poll.objects.all()
[]

# Create a new Poll.
# Support for time zones is enabled in the default settings file, so
# Django expects a datetime with tzinfo for pub_date. Use timezone.now()
# instead of datetime.datetime.now() and it will do the right thing.
>>> from django.utils import timezone
>>> p = Poll(question="What's new?", pub_date=timezone.now())

# Save the object into the database. You have to call save() explicitly.
>>> p.save()

# Now it has an ID. Note that this might say "1L" instead of "1", depending
# on which database you're using. That's no biggie; it just means your
# database backend prefers to return integers as Python long integer
# objects.
>>> p.id
1

# Access database columns via Python attributes.
>>> p.question
"What's new?"
>>> p.pub_date
datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)

# Change values by changing the attributes, then calling save().
>>> p.question = "What's up?"
>>> p.save()

# objects.all() displays all the polls in the database.
>>> Poll.objects.all()
[<Poll: Poll object>]




 <Poll: Poll object> is, utterly, an unhelpful representation of this object. Let’s fix that by editing the polls model (in the polls/models.py file) and adding a __unicode__() method to both Poll and Choice. On Python 3, simply replace__unicode__ by __str__ in the following example:


from django.db import models

class Poll(models.Model):
    # ...
    def __unicode__(self):  # Python 3: def __str__(self):
        return self.question

class Choice(models.Model):
    # ...
    def __unicode__(self):  # Python 3: def __str__(self):
        return self.choice_text





It’s important to add __unicode__() methods (or __str__() on Python 3) to your models, not only for your own sanity when dealing with the interactive prompt, but also because objects’ representations are used throughout Django’s automatically-generated admin.

Save these changes and start a new Python interactive shell by running python manage.py shell again:


>>> from polls.models import Poll, Choice

# Make sure our __unicode__() addition worked.
>>> Poll.objects.all()
[<Poll: What's up?>]

# Django provides a rich database lookup API that's entirely driven by
# keyword arguments.
>>> Poll.objects.filter(id=1)
[<Poll: What's up?>]
>>> Poll.objects.filter(question__startswith='What')
[<Poll: What's up?>]

# Get the poll that was published this year.
>>> from django.utils import timezone
>>> current_year = timezone.now().year
>>> Poll.objects.get(pub_date__year=current_year)
<Poll: What's up?>

# Request an ID that doesn't exist, this will raise an exception.
>>> Poll.objects.get(id=2)
Traceback (most recent call last):
    ...
DoesNotExist: Poll matching query does not exist. Lookup parameters were {'id': 2}

# Lookup by a primary key is the most common case, so Django provides a
# shortcut for primary-key exact lookups.
# The following is identical to Poll.objects.get(id=1).
>>> Poll.objects.get(pk=1)
<Poll: What's up?>

# Make sure our custom method worked.
>>> p = Poll.objects.get(pk=1)
>>> p.was_published_recently()
True

# Give the Poll a couple of Choices. The create call constructs a new
# Choice object, does the INSERT statement, adds the choice to the set
# of available choices and returns the new Choice object. Django creates
# a set to hold the "other side" of a ForeignKey relation
# (e.g. a poll's choices) which can be accessed via the API.
>>> p = Poll.objects.get(pk=1)

# Display any choices from the related object set -- none so far.
>>> p.choice_set.all()
[]

# Create three choices.
>>> p.choice_set.create(choice_text='Not much', votes=0)
<Choice: Not much>
>>> p.choice_set.create(choice_text='The sky', votes=0)
<Choice: The sky>
>>> c = p.choice_set.create(choice_text='Just hacking again', votes=0)

# Choice objects have API access to their related Poll objects.
>>> c.poll
<Poll: What's up?>

# And vice versa: Poll objects get access to Choice objects.
>>> p.choice_set.all()
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
>>> p.choice_set.count()
3

# The API automatically follows relationships as far as you need.
# Use double underscores to separate relationships.
# This works as many levels deep as you want; there's no limit.
# Find all Choices for any poll whose pub_date is in this year
# (reusing the 'current_year' variable we created above).
>>> Choice.objects.filter(poll__pub_date__year=current_year)
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]

# Let's delete one of the choices. Use delete() for that.
>>> c = p.choice_set.filter(choice_text__startswith='Just hacking')
>>> c.delete()

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Sunday, 2 June 2013

Your first Django application (Part-1)

Create a project

Database setup