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Django when is concrete inheritance appropriate

Let me start by stating that I have looked at django-polymorphic for this and still have questions. I have item models and many subtypes for items. Currently, my models look like this.
class Item(models.Model):
pass
class Television(Item):
upc = models.CharField(max_length=12, null=True)
title = models.CharField(max_length=255, null=True)
brand = models.ForeignKey(Brand)
screen_size = models.IntegerField()
class Fridge(Item):
upc = models.CharField(max_length=12, null=True)
title = models.CharField(max_length=255, null=True)
brand = models.ForeignKey(Brand)
stuff_about_fridge = models.CharField(max_length=255, null=True)
I did this at first because then I wouldn't worry about all of the left joins when querying different item types that would be caused if my models looked like this:
class Item(models.Model):
upc = models.CharField(max_length=12, null=True)
title = models.CharField(max_length=255, null=True)
brand = models.ForeignKey(Brand)
class Television(Item):
screen_size = models.IntegerField()
class Fridge(Item):
stuff_about_fridge = models.CharField(max_length=255, null=True)
I am now reaching a point where I realize that I very often query all of the Item models together and have to left join information from the subtypes instead, so I am not really saving myself there. My question is, even if I used something like django-polymorphic, would it make sense to A) put everything that is shared in the parent model and just specific things in the child models or to B) have it like I do where everything is in the child model, but they share a parent model PK just so that they can be queried together?

"Abstract base classes are useful when you want to put some common information into a number of other models. This model will then not be used to create any database table. Instead, when it is used as a base class for other models, its fields will be added to those of the child class"
Reference: https://docs.djangoproject.com/en/3.0/topics/db/models/#abstract-base-classes
The point of using inheritance is for sharing common info as mentioned in option (A).
Django-polymorphic makes using inherited models easier, nothing more.
Reference: https://django-polymorphic.readthedocs.io/en/stable/
That means, in conclusion, option (A) is correct even though if you use Django-polymorphic.
Below method is the right approach:
class Item(models.Model):
upc = models.CharField(max_length=12, null=True)
title = models.CharField(max_length=255, null=True)
brand = models.ForeignKey(Brand)
class Television(Item):
screen_size = models.IntegerField()
class Fridge(Item):
stuff_about_fridge = models.CharField(max_length=255, null=True)

Using Model.objects.all() as a blueprint for a secondary table entry

I am having a bit of trouble with the logic of how this should work so I am hoping it is possible.
I figured out 1 possible solution that is written as an answer below, I will accept it in a few days, but if someone comes up with a better solution, I will negate any answer I post.
Overall I am working on an Apartment Move-Out/Move-In Inspection Application in Django, and in both portions I have universal Locations that must be inspected for each report. I have allowed the InspectionLocations objects to be updated/submitted by clients, which is presenting an issue in how submitted reports should be stored in my Database.
What I want is to use the InspectionLocations table as a blueprint to build an Inspection Report for Move-Ins where the form-fields are generated based on the InspectionLocations objects' location, status, and information attributes/fields.
My issue is right at this point, how do I reference those values as a blueprint to build a report submission when the number of fields in the InspectionLocations can change?
from django.db import models
from apps.units.models import Unit
class Inspections(models.Model):
class Meta:
abstract = True
id = models.AutoField(primary_key=True)
inspection_date = models.DateField()
submitted_by = models.ForeignKey(
'users.CustomUser',
default=None,
null=True,
on_delete=models.SET_NULL,
db_column='submitted_by')
last_update = models.DateTimeField(auto_now=True)
date_added = models.DateTimeField(auto_now_add=True, editable=False)
class MoveInInspections(Inspections):
unit = models.ForeignKey(Unit, on_delete=models.CASCADE, db_column='unit_id')
# should have reference to all InspectionLocation items as reference for submission, how?
class MoveOutInspections(Inspections):
unit = models.ForeignKey(Unit, on_delete=models.CASCADE, db_column='unit_id')
date_notice_given = models.DateField(blank=True, null=True, default=None)
date_vacated = models.DateField(blank=True, null=True, default=None)
# should have reference to all InspectionLocation items as reference for submission, how?
class InspectionLocations(models.Model):
'''
Defualt Inspection Locations are created when a
client is created using code like this:
InspectionLocation.objects.get_or_create(location='Living Room')
InspectionLocation.objects.get_or_create(location='Dining Room')
InspectionLocation.objects.get_or_create(location='Kitchen')
InspectionLocation.objects.get_or_create(location='Bedroom')
InspectionLocation.objects.get_or_create(location='Bathroom')
InspectionLocation.objects.get_or_create(location='Other')
'''
id = models.AutoField(primary_key=True)
location = models.CharField(max_length=50)
status = models.BooleanField(default=None)
information = models.TextField(default=None, blank=True)
I have tried ManyToMany fields and FKs but I cannot seem to get the logic working as anytime an object references an InspectionLocations object it is universally changing data for every report, which is leading be to the idea that I somehow need to use it as a blueprint.

I didn't post this in my question because it was getting long, but my best option so far seems to be to use a Django JSONField (as I am using Postgres), like so:
from django.contrib.postgres.fields import JSONField
class MoveInInspections(Inspections):
unit = models.ForeignKey(Unit, on_delete=models.CASCADE, db_column='unit_id')
data = JSONField()
class MoveOutInspections(Inspections):
unit = models.ForeignKey(Unit, on_delete=models.CASCADE, db_column='unit_id')
date_notice_given = models.DateField(blank=True, null=True, default=None)
date_vacated = models.DateField(blank=True, null=True, default=None)
data = JSONField()
To where I store the values of the InspectionLocations object's in a Dictionary

Duplicating an Imagefield on save() - django

I'm working on a project in django, I need to duplicate a picture stored in one model and save it with a different name into another one, I've tried many of the responses I've found but nothing seems to work.
This last try doesn't give me an error but is not duplicating the image, nor storing a copy with the name. I'm running Pillow and Django 3.X
models.py:
class Visualization(models.Model):
kind = models.CharField(max_length=90)
description = models.CharField(max_length=90)
image = models.ImageField(upload_to='visualization', null=True,
blank=True)
class Order(models.Model):
visualization = models.ForeignKey(Visualization,
on_delete=models.CASCADE)
hashed = models.ImageField(upload_to='hashedimages', null=True,
blank=True)
def save(self):
super().save()
self.hashed = self.visualization.image
self.hashed.name = 'randomothername.jpg''
self.hashed.save()

Django - get_or_create() with auto_now=True

I’m using Django and I'm having a problem with a Python script that uses Django models
The script that I'm using takes data from an api and loads it into my database.
my model:
class Movie(models.Model):
title = models.CharField(max_length=511)
tmdb_id = models.IntegerField(null=True, blank=True)
release = models.DateField(null=True, blank=True)
poster = models.TextField(max_length=500, null=True)
runtime = models.IntegerField(null=True, blank=True)
description = models.TextField(null=True, blank=True)
edit = models.DateTimeField(auto_now=True, null=True, blank=True)
backdrop = models.TextField(max_length=500, null=True, blank=True)
popularity = models.TextField(null=True, blank=True)
the script:
movies = tmdb.Movies().upcoming()
results = movies['results']
ids = []
for movie in results:
data, created = Movie.objects.get_or_create(title=movie['title'],
tmdb_id=movie['id'],
release=movie['release_date'],
description=movie['overview'],
backdrop=movie['backdrop_path'],
poster=movie['poster_path'],
popularity=movie['popularity'])
The problem I'm having is that whenever I run the script, the entries are duplicated because the edit field is change, but the purpose I put the edit field is to know when exactly a movie got edited, ie: some other field got changed.
How can I avoid the duplicates, but also keep the edit field in case some real change happened?

but the purpose I put the edit field is to know when exactly a movie
got edited, ie: some other field got changed.
That probably means you are using the wrong function. You should be using update_or_create istead.
A convenience method for updating an object with the given kwargs,
creating a new one if necessary. The defaults is a dictionary of
(field, value) pairs used to update the object.
This is different from get_or_create, which creates an object if it does not exists, or simply fetches it when it does exist. update_or_create is the one that does the actually updating.
However, changing to this method doesn't solve this:
How can I avoid the duplicates, but also keep the edit field in case
some real change happened?
Duplicates are created because you do not have a unique index on any of your fields. Both get_or_create and update_or_create require that you have a unique field. It seems that the following change is in order:
class Movie(models.Model):
title = models.CharField(max_length=511)
tmdb_id = models.IntegerField(unique=True)

Preserve url in django ImageField when copying to a new model instance

I am performing a data migration, moving images from inside one model out to their own model.
class OldCrappyModel(models.Model):
...
original_image = models.ImageField(upload_to=upload_original_image, null=True, blank=True)
my_events_image = models.ImageField(upload_to=upload_my_promotions_image, null=True, blank=True)
...
class MyImage(models.Model):
original_image = models.ImageField(upload_to=upload_original_image, null=True, blank=True)
my_events_image = models.ImageField(upload_to=upload_my_promotions_image, null=True, blank=True)
...
The upload_to methods just return a unique name for the file.
When I go to migrate them (in a South datamigration):
i = MyImage(
my_events_image = old.my_events_image,
original_image = old.original_image,
)
i.save()
The problem is, we have some images that are not in the same place as the new ones. When the copy happens, it translates the url from the old ImageField into a url that would work for the new one. For example:
old.url comes out to path/to/something/awesome.jpg
i.url becomes new/media/root/awesome.jpg
How can I preserve the ImageField without anything happening to it when it saves? I'd like to avoid having to make new copies of all the files if possible.

Disable upload_to for the duration of the migration. Set the upload_to manually while copying instances.
After the migration, enable it back.