In many applications, you might encounter scenarios where you need to ensure that a pair of fields in a database model must be unique together. For example, if you have a Booking model in a restaurant reservation system, you may want to ensure that the combination of table_number and reservation_time is unique, preventing double bookings for the same table at the same time. In Django, this can be achieved using the unique_together constraint. This article will guide you through creating a small project in Django to demonstrate how to define two fields as a unique couple.

Define Two Fields “Unique” as Couple in Django

Setting Up Your Django Project

First, ensure you have Django installed. If not, you can install it using pip:

pip install django

Next, create a new Django project:

django-admin startproject unique_fields_project
cd unique_fields_project

Create a new app within your project:

python manage.py startapp reservations

Add the new app to your INSTALLED_APPS in unique_fields_project/settings.py:

INSTALLED_APPS = [
    ...
    'reservations',
]

Defining the Model with Unique Together Constraint

In your reservations/models.py, define a Booking model with the unique_together constraint: The unique_together constraint ensures that each combination of table_number and reservation_time is unique.

from django.db import models

class Booking(models.Model):
    table_number = models.IntegerField()
    reservation_time = models.DateTimeField()
    
    class Meta:
        unique_together = ('table_number', 'reservation_time')
        
    def __str__(self):
        return f'Table {self.table_number} at {self.reservation_time}'

Update admin.py file also

from django.contrib import admin
from reservations.models import Booking
# Register your models here.

admin.site.register(Booking)

Creating and Applying Migrations

To create the database table for your model, generate and apply migrations:

python manage.py makemigrations
python manage.py migrate

Createsuperuser

python manage.py createsuperuser

Testing the Unique Constraint

Run the server and testing the unique constraint

Output