Collection of useful Django snippets for several purposes

Index

Project structure
Manage dev and production settings
Create a slug
Send email
Database dump to file
Provide data to DB via Django Python Shell
Create script with access to Django shell
Migrate Django from SQLite to PostgreSQL
Using Django Messages with Bootstrap
Override form __init__ method
Switch to a new Database

Project structure

Below is an example of a structure for a large project that contains a Django app.¹ ²

project/
│
├── app/
│   ├── __init__.py
│   ├── admin.py
│   ├── apps.py
│   │
│   ├── migrations/
│   │   └── __init__.py
│   │
│   ├── models.py
│   ├── tests.py
│   └── views.py
│
├── docs/
│
├── project/
│   ├── __init__.py
│   ├── settings.py
│   ├── urls.py
│   └── wsgi.py
│
├── static/
│   └── style.css
│
├── templates/
│   └── base.html
│
├── .gitignore
├── manage.py
├── LICENSE
└── README.md

Manage dev and production settings

When working with Django it is often useful/needed to have different settings for development and production. One way to handle this is to have separate setting files for each case.¹ ² For instance, settings.py for production and settings_dev.py for development. The DJANGO_SETTINGS_MODULE environment variable controls which settings file Django will load. So, in development, we can:

set DJANGO_SETTINGS_MODULE=mysite.settings_dev
python manage.py runserver

Alternatively we can speciffy the settings file when calling the manage.py:

set DJANGO_SETTINGS_MODULE=mysite.settings_dev
python manage.py runserver --settings=settings_dev

However, this will not work when doing migrations. So if you required different settings when migrating, the first methods is probably better.

Create a slug

Call the Django slugify function automatically by overriding the save method. It is preferable to generate the slug only once when you create a new object, otherwise your URLs may change when the q field is edited, which can cause broken links. More info here.

# models.py

from django.utils.text import slugify

class Test(models.Model):
    q = models.CharField(max_length=30)
    s = models.SlugField()

    def save(self, *args, **kwargs):
        if not self.id:
            # Newly created object, so set slug
            self.s = slugify(self.q)

        super(Test, self).save(*args, **kwargs)

Send email

If html_message keyword argument is provided, the resulting email will be a multipart/alternative email with message as the text/plain content type and html_message as the text/html content type.

# views.py

from django.core.mail import send_mail

send_mail(
    'Subject here',
    'Here is the message.',
    'from@example.com',
    ['to@example.com'],
    fail_silently=False,
)

Mail is sent using the SMTP host and port specified in the EMAIL_HOST and EMAIL_PORT settings. The EMAIL_HOST_USER and EMAIL_HOST_PASSWORD settings, if set, are used to authenticate to the SMTP server, and the EMAIL_USE_TLS and EMAIL_USE_SSL settings control whether a secure connection is used. More info here.

Database dump to file

Save from DB

$ python manage.py dumpdata > db_dump.json

Load fixture to DB

$ python manage.py loaddata <fixture>

Provide data to DB via Django Python Shell

Exemple for loading data in a json file named filename.json to the Model Member in the app website

$ python manage.py shell

>>> import json
>>> from website.models import Member
>>> with open('filename.json', encoding="utf-8") as f:
...     members_json = json.load(f)
...
>>> for member in members_json:
...     member = Member(name=member['name'], position=member['position'], alumni=member['alumni'])
...     member.save()
...
>>> exit()

Create script with access to Django shell

If you want to run an external script but have access to the Django environment like you do with python manage.py shell you can do the following. More info here

# your_script.py

import os

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "your_project_name.settings")

# your imports, e.g. Django models
from your_project_name.models import Location

# From now onwards start your script..

Here is an example to access and modify your model:

# models.py

class Location(models.Model):
    name = models.CharField(max_length=100)

# your_script.py

if __name__ == '__main__':    
    # e.g. add a new location
    l = Location()
    l.name = 'Berlin'
    l.save()

    # this is an example to access your model
    locations = Location.objects.all()
    print locations

    # e.g. delete the location
    berlin = Location.objects.filter(name='Berlin')
    print berlin
    berlin.delete()

Alternatively

Create your script and run it from within the python shell:

$ python manage.py shell

>>> exec(open("filename.py").read())

This will read and run the contents of the file. Works on Python 3.

Migrate Django from SQLite to PostgreSQL

Here's how to migrate a Django database from SQLite to PostgreSQL. More info here.

Dump existing data:

python manage.py dumpdata > datadump.json

Change settings.py to Postgres backend.
Make sure you can connect on PostgreSQL. Then:

python manage.py migrate --run-syncdb

Run this on Django shell to exclude contentype data

python manage.py shell

>>> from django.contrib.contenttypes.models import ContentType
>>> ContentType.objects.all().delete()
>>> quit()

Finally:

python manage.py loaddata datadump.json

Using Django Messages with Bootstrap

Configure the Django Messages Framework to work with Bootstrap by changing the MESSAGE_TAGS. In the settings.py file:

from django.contrib.messages import constants as messages

MESSAGE_TAGS = {
    messages.DEBUG: 'info',
    messages.INFO: 'info',
    messages.SUCCESS: 'success',
    messages.WARNING: 'warning',
    messages.ERROR: 'danger',
}

In your HTML base template insert the section where messages will display:

{% if messages %}
  {% for message in messages %}
    <div class="alert alert-{{ message.tags }} alert-dismissible" role="alert">
      <button type="button" class="close" data-dismiss="alert" aria-label="Close">
        <span aria-hidden="true">&times;</span>
      </button>
      {{ message }}
    </div>
  {% endfor %}
{% endif %}

To use messages do the following in views.py:

from django.contrib import messages

messages.debug(request, '%s SQL statements were executed.' % count)
messages.info(request, 'Three credits remain in your account.')
messages.success(request, 'Profile details updated.')
messages.warning(request, 'Your account expires in three days.')
messages.error(request, 'Document deleted.')

Override form `init` method

You can change how a form is created base on logic from a view by modifying the form __init__ method.

# forms.py

class TransactionForm(forms.ModelForm):

    class Meta:
        model = Transaction
        fields = ('category', 'name', 'value', 'split')

    # Override init method so that the split field only shows in forms of account with more than one user
    def __init__(self, *args, **kwargs):
        multiple_users = kwargs.pop('multiple_users', True)
        super(TransactionForm, self).__init__(*args, **kwargs)
        if not multiple_users:
            del self.fields['split']

In the views.py file you pass the multiple_users variable to the form class

# views.py

def transaction_new(request, account_id):
    if request.method == "POST":
        form = TransactionForm(request.POST, multiple_users=multiple_users)
        if form.is_valid():
            transaction.save()
            return redirect('transaction_new', account_id=account_id)
        else:
            form = TransactionForm(multiple_users=multiple_users)
    context = {...}
	return render(request, 'expense_tracker/new_transaction.html', context)

Switch to a new Database

1) Add the new Database to `settings.py`

Edit your settings.py and add the new database to the DATABASES list and give it the name "new". For example, I am using the MySQL database, so I will add the "new" dictionary:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    },
    'new': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'tFnXEEpcjQ',
        'USER': 'tFnXEEpcjQ',
        'PASSWORD': 'UW9BWCT8m2',
        'HOST': 'remotemysql.com',
        'PORT': '3306',
    }
}

I have used the MySQL database in this example. You will add the code for the database that you are using. Note: You need to install the client for whatever database you are using on your machine.

2) Create tables in the new Database

Make sure that you have not deleted the migrations folder. If you have deleted it by accident, make migrations again.

To create tables in your new database, run the migrations on it using the following command:

python manage.py migrate --database=new

3) Transfer data to the new Database (optional)

You can skip this step if you do not want to transfer the data from your old database to the new one.

First, clear the new database by running the following command:

python manage.py flush --database=new

Export data from your current database to a JSON file using the following command:

python manage.py dumpdata>data.json

Now load data into the new database using the following command:

python manage.py loaddata data.json --database=new

4) Remove the old Database

Now remove the old database from settings.py and rename the "new" database to "default". My final DATABASES look like this:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'tFnXEEpcjQ',
        'USER': 'tFnXEEpcjQ',
        'PASSWORD': 'UW9BWCT8m2',
        'HOST': 'remotemysql.com',
        'PORT': '3306',
    }
}

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django-snippets.md

django-snippets.md

Collection of useful Django snippets for several purposes

Index

Project structure

Manage dev and production settings

Create a slug

Send email

Database dump to file

Provide data to DB via Django Python Shell

Create script with access to Django shell

Migrate Django from SQLite to PostgreSQL

Using Django Messages with Bootstrap

Override form `init` method

Switch to a new Database

1) Add the new Database to `settings.py`

2) Create tables in the new Database

3) Transfer data to the new Database (optional)

4) Remove the old Database

Files

django-snippets.md

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django-snippets.md

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Collection of useful Django snippets for several purposes

Index

Project structure

Manage dev and production settings

Create a slug

Send email

Database dump to file

Provide data to DB via Django Python Shell

Create script with access to Django shell

Migrate Django from SQLite to PostgreSQL

Using Django Messages with Bootstrap

Override form __init__ method

Switch to a new Database

1) Add the new Database to settings.py

2) Create tables in the new Database

3) Transfer data to the new Database (optional)

4) Remove the old Database

Override form `init` method

1) Add the new Database to `settings.py`