lostplaces-backend/source/lostplaces/lostplaces_app/models.py

import os
import uuid

from django.db import models
from django.dispatch import receiver
from django.contrib.auth.models import AbstractUser
from django_thumbs.fields import ImageThumbsField

# Create your models here.

# Custom user model
class Explorer(AbstractUser):
    # add additional fields in here

    def __str__(self):
        return self.username

# Place defines a lost place (location, name, description etc.).
class Place (models.Model):
    name = models.CharField(max_length=50)
    location = models.CharField(max_length=50)
    latitude = models.FloatField()
    longitude = models.FloatField()
    description = models.TextField()

    def __str__(self):
        return self.name

# Define callback that generates /path/to/image.ext as filename.
def generate_image_upload_path(instance, filename):
    return 'places/' + str(uuid.uuid4())+'.'+filename.split('.')[-1]

class PlaceImage (models.Model):
    filename = ImageThumbsField(
        upload_to=generate_image_upload_path,
        max_length=50,
        sizes=(
            {'code': 'thumbnail', 'wxh': '390x390'},
            {'code': 'hero', 'wxh': '700x700'},
            {'code': 'large', 'wxh': '1920x1920'}
        )
    )
    place = models.ForeignKey(Place, on_delete=models.CASCADE, related_name='images')
    description = models.TextField(blank=True)

    def __str__(self):
        return ' '.join([self.place.name, str(self.pk)])

# These two auto-delete files from filesystem when they are unneeded:

@receiver(models.signals.post_delete, sender=PlaceImage)
def auto_delete_file_on_delete(sender, instance, **kwargs):
    """
    Deletes file from filesystem
    when corresponding `PlaceImage` object is deleted.
    """
    if instance.filename:
        if os.path.isfile(instance.filename.path):
            os.remove(instance.filename.path)

@receiver(models.signals.pre_save, sender=PlaceImage)
def auto_delete_file_on_change(sender, instance, **kwargs):
    """
    Deletes old file from filesystem
    when corresponding `PlaceImage` object is updated
    with new file.
    """
    if not instance.pk:
        return False

    try:
        old_file = PlaceImage.objects.get(pk=instance.pk).filename
    except PlaceImage.DoesNotExist:
        return False

    new_file = instance.filename
    if not old_file == new_file:
        if os.path.isfile(old_file.path):
            os.remove(old_file.path)