Rapid development with a database

Kory Hutchison - 15 May 2019

Alright. So in my previous tutorial I went over how to set up a basic Django project and connect it to a PostgreSQL database. So now that we have a database connected, most likely when you start developing you’ll test a variety of scenarios and make modifications to the data in your database. So how do you easily revert those changes? Is there a way to make it so there is always specific default data in your database to work with? Let me show you how.

Create the file

So first we are going to create a file called initialize.py. You can call it whatever you want, but that’s what I call it. We’re going to use this file to work all of this magic that I speak of. I like this file to be in the same directory as manage.py. Just to keep things organized.

Start out the file with these lines:

import django from django.core import management from django.db import connection import os, sys # ensure the user really wants to do this confirm = input(''' Do you want to drop and recreate the entire database? Please type 'yes' to confirm the data destruction: ''') if confirm.lower() != 'yes': print() print(' exiting') sys.exit(1) # initialize the django environment os.environ['DJANGO_SETTINGS_MODULE'] = '[your project name].settings' django.setup()

Up until this point, all we are doing is importing the libraries that we need, confirming with the user that they actually want to delete the database, and letting Django know what settings file to look for when setting up. You’ll need to put your project name in there so that it works for you.

Next we are going to add the code to delete the database and perform the migrations again. We’ll do that with the following code:

# drop and recreate the database tables print() print('Living on the edge! Dropping the current database tables.') with connection.cursor() as cursor: cursor.execute("DROP SCHEMA public CASCADE") cursor.execute("CREATE SCHEMA public") cursor.execute("GRANT ALL ON SCHEMA public TO postgres") cursor.execute("GRANT ALL ON SCHEMA public TO public") # make the migrations and migrate management.call_command('makemigrations') management.call_command('migrate')

So you might be wondering what the public schema is. Every database in PostgreSQL has a schema called public. So unless you have created a schema yourself, then this is what you’ll want. Also, pay attention to the third line in the cursor and how it grants access to postgres. That’s the user/owner that you tied to the database. You might need to look in pgAdmin to see if the user is different, but most likely this is the same for you. Then you can see that we run the same commands that we ran in my previous tutorial for moving the models into the database.

Now that we have the whole database wipe part finished, let’s move on to seeding it with data.

Create App and Model

So if we want to seed the database, we probably want a model to seed with. I’ll show you how to leverage Django’s AbstractUser model to create your user models. First we’ll need to create an app. Make sure you’re in the same directory as manage.py and run this:

python manage.py startapp account

Going along with my typical conventions, I’m naming it account because this would be where you would have all your pages for the user’s account. And it makes logical sense to put the user model here.

After running that command you’ll now see a models.py file. Open it up and place the following in there:

from django.contrib.auth.models import AbstractUser class ExampleUser(AbstractUser): # id # username # password # first_name # last_name # email # last_login # is_superuser # is_staff # is_active # date_joined phone = models.CharField(max_length=10)

What we’re doing is subclassing the AbstractUser class. AbstractUser is a default class that comes with Django. To help me remember the fields that come from AbstractUser, I like to add them as comments inside of the class. For simplicity sake, I added a phone number field to the class, but in reality you probably would add more too it. Such as address information. Now that we have app and model created, head over to settings.py.

We need to add 2 things in this file. First, we need to tell Django that the account app exists. On line 33 you’ll find an array called INSTALLED_APPS. Add your account app to it so it looks like this:

INSTALLED_APPS = [ 'django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles', 'account' ]

Then at the very bottom of the file, we need to tell Django what model it should use for authentication. Since we created our own user model, we define it like so:

AUTH_USER_MODEL = 'account.ExampleUser'

Now that we have all the setup in place, go ahead and run initialize.py.

python initialize.py

You should see it output that there was a new migration created for account, and it will show all the migrations being performed. If you see “No changes detected”, you might need to just run the migrations manually. Note: you can run migrations for just a specific app by putting the app name after “makemigrations”.

Add data to initialize.py

Go ahead and open initialize.py and add the following lines:

from account import models as amod user = amod.ExampleUser() user.first_name = 'John' user.last_name = 'Smith' user.username = 'john.smith' user.set_password('Password1') user.email = 'john.smith@example.com' user.phone = '1234567890' user.save()

When we run initialize.py again, this will create a user in our database. I like to create my objects like this because I think this is a more simple way to read it. You can also add the properties as parameters or even use the create method. You can see all those different options here. But what’s really important is putting .save() at the end of it all. Without that, Django won’t put anything into the database.

Go ahead and run initialize.py, and then look in pgAdmin to see if the user shows up! This file can be incredibly useful when things get messed up in your database during development. I find it super handy, and I hope you do too!