Creating a unique object using DateField() - django

Question

I would just like to create a model that essentially prevents the same date being selected by two different users (or the same user).
E.g if User1 has selected 2019-01-10 as a "date" for a booking, then User2 (or any other Users) are not able to create an object with that same date.
I have created a very basic model that can allow different Users to create an object using the DateField(). Using the Django admin page, I can create different instances of objects by two different Users (admin and Test_User).
In order to try to ensure that a new object can't be created if that date has already been used by a different object I have tried the following approach:
a compare function that utilizes __dict__.
models.py
from __future__ import unicode_literals
from django.db import models, IntegrityError
from django.db.models import Q
from django.contrib.auth.models import User
from datetime import datetime
class Booking(models.Model):
date = models.DateField(null=False, blank=False)
booked_at = models.DateTimeField(auto_now_add=True)
booking_last_modified = models.DateTimeField(auto_now=True)
class PersonalBooking(Booking):
user = models.ForeignKey(User, on_delete=models.CASCADE)
def compare(self, obj):
excluded_keys = 'booked_at', '_state', 'booking_last_modified', 'user',
return self._compare(self, obj, excluded_keys)
def _compare(self, obj1, obj2, excluded_keys):
d1, d2 = obj1.__dict__, obj2.__dict__
for k,v in d1.items():
if k in excluded_keys:
continue
try:
if v != d2[k]:
pass
except IntegrityError as error:
print(error)
print('Date already selected by different User. Please select another date.')
admin.py
from django.contrib import admin
from . import models
from .models import Booking, PersonalBooking
class PersonalBookingAdmin(admin.ModelAdmin):
list_display = ('format_date', 'user', )
def format_date(self, obj):
return obj.date.strftime('%d-%b-%Y')
format_date.admin_order_field = 'date'
format_date.short_description = 'Date'
def user(self, obj):
return obj.user()
user.admin_order_field = 'user'
user.short_description = 'User'
admin.site.register(models.PersonalBooking, PersonalBookingAdmin)
It didn't work as I had hoped, objects with the same date could still be created by the same or different users. Perhaps there is a simpler way? Or maybe I need to use the Q() class? I am not very familiar with it.
Any help is greatly appreciated.
Thanks.

Answer 1

You could do this validation at the database level by setting the unique attribute to True in your model's field.
class Booking(models.Model):
date = models.DateField(null=False, blank=False, unique=True)
booked_at = models.DateTimeField(auto_now_add=True)
booking_last_modified = models.DateTimeField(auto_now=True)
But this would present issues if the field was changed later to store time.
If you are going to be storing the time as well, you could override the model's default save function to check that there isn't another Booking with the same date (__date) each time it is saved. exists() returns True if there is a match, so this will throw a ValidationError if there is a match.
from django.core.exceptions import ValidationError
class Booking(models.Model):
date = models.DateTimeField(null=False, blank=False)
booked_at = models.DateTimeField(auto_now_add=True)
booking_last_modified = models.DateTimeField(auto_now=True)
def save(self, *args, **kwargs):
# Make sure there are no bookings on the same day
if Booking.objects.exclude(pk=self.pk).filter(date__date=self.date.date).exists():
raise ValidationError('There cannot be two bookings with the same date.')
super(Booking, self).save(*args, **kwargs)

Answer 2

Try this
https://docs.djangoproject.com/en/2.1/ref/models/fields/#unique-for-date
For user column set unique_for_date=True