I have a django app which basically is just a photo album. Right now I have two models: Image and Album. Among other things, each Album has a foreign key to an Image to be its thumbnail and each Image has a foreign key to the Album it belongs in. However, when I try to use manage.py syncdb or manage.py sqlall I get errors saying the class not defined first in models.py isn't defined when it is used in the first class defined.
models.py (abridged):
from django.db import models
import os
class Album(models.Model):
thumb = models.ForeignKey(Image, null=True, blank=True)
class Image(models.Model):
image = models.ImageField(upload_to='t_pics/images')
thumb = models.ImageField(upload_to='t_pics/images/thumbs')
album = models.ForeignKey(Album)
Error I get when I do manage.py sqlall appname:
[...]
File "/path/to/file/appname/models.py", line 4, in ?
class Album(models.Model):
File "/path/to/file/appname/models.py", line 5, in Album
thumb = models.ForeignKey(Image, null=True, blank=True)
NameError: name 'Image' is not defined
I get the same error when I switch the order of the classes in models.py except it says 'Album' undefined instead of 'Image' undefined I also tried commenting the dependancy in the first class then uncommenting after everything else was successfully imported but that didn't help. How should I go about making this work? I'm reluctant to make an entire third class Thumb because it will have a lot of the same code as Image I'm also pretty sure I could manually add the foreign key to the database but I want this to be clean and not hackish.
You don't actually have a circular reference; the issue is that, at the time you define Album, you haven't defined Image yet. You can fix that by using a string instead:
class Album(models.model):
thumb = models.ForeignKey('Image', null=True, blank=True)
However, in this case, you might want to use a OneToOneField instead of a foreign key. (Note that you'll still have to use the trick with the string, though).
Use quotes to force a lazy reference:
models.ForeignKey('Image', null=True, blank=True)
Also, ForeignKey.related_name is your friend (avoids back-reference name clashes).
This is old but anyway, i'd like to say that I don't see a reason for attribute album in model Image. In my opinion, it is not really needed.
Related
I've been building a Django website and included a UUID field "customer_id" in my initial "Customer" model. Finally, I decided to drop it. But when I try to delete it from my models.py, Django throws
SystemCheckError: System check identified some issues:
ERRORS:
<class 'accounts.admin.CustomerAdmin'>: (admin.E035) The value of 'readonly_fields[1]' is not a callable, an attribute of 'CustomerAdmin', or an attribute of 'accounts.Customer'.
Here is the code of models.py
from django.db import models
import uuid
# Create a base model to make sure we keep track of creation and edits
class ModelBaseClass(models.Model):
date_created = models.DateTimeField(auto_now_add=True, null=True)
date_modified = models.DateTimeField(auto_now=True, null=True)
class Meta:
abstract = True
# Create your models here.
class Customer(ModelBaseClass):
customer_id = models.UUIDField(default=uuid.uuid4, #this is the field i try to drop
editable=False,
unique=True)
name = models.CharField(max_length=200, null=True)
email = models.CharField(max_length=200, null=True)
def __str__(self):
return self.name
What I tried so far:
I suspect that this could be related to existing data or some other dependencies. So...
I deleted the sqlite database, deleted all migration files and ran
"python manage.py makemigrations" and "python manage.py migrate".
I ran python manage.py flush.
I also tried to change the editable=False to editable=True and migrate before dropping,
but it didn't change anything.
It's perhaps also worth mentioning that my "Customer" model a relation to another model.
Could someone explain me why Django is preventing me from deleting this field and how to resolve this?
Thanks! :)
Could someone explain me what's going on and how to resolve this?
As the error says, you have a model admin named CustomerAdmin. Indeed:
<class 'accounts.admin.CustomerAdmin'>: (admin.E035) The value of 'readonly_fields[1]' is not a callable, an attribute of 'CustomerAdmin', or an attribute of 'accounts.Customer'.
For the readonly_fields, it lists the customer_id, but since that field is no longer available, it raises the error.
I'm building a simple recipe app, and so far I have two models: Ingredient and Recipe.
Each recipe should have multiple ingredients, so I laid out my model like this:
class Ingredient(models.Model):
name = models.CharField(max_length=50)
class Recipe(models.Model):
title = models.CharField(max_length=100)
ingredients = models.ForeignKey(Ingredient, on_delete=CASCADE)
instructions = JSONField()
date_posted = models.DateTimeField(default=timezone.now)
author = models.ForeignKey(User, on_delete=SET_DEFAULT, default='Chef Anon')
When I makemigrations, I get nothing, but when I migrate, I get this ValueError:
ValueError: Cannot alter field cookbook.Recipe.ingredients into cookbook.Recipe.ingredients - they do not properly define db_type (are you using a badly-written custom field?)
Following the example here (Django: Add foreign key in same model but different class), I've tried setting ingredients=models.ForeignKey(Ingredient, on_delete=CASCADE) as well as using lazy syntax ingredients=models.ForeignKey("Ingredient", on_delete=CASCADE), but each time, makemigrations shows no changes, and migrate gives me the same ValueError.
Edit
My imports:
from django.db.models.deletion import CASCADE, SET_DEFAULT, SET_NULL
from django.db.models.fields.json import JSONField
from django.utils import timezone
from django.contrib.auth.models import User```
Try replacing on_delete=CASCADE with on_delete=models.CASCADE
If you have not imported CASCADE separately from models.
All though, in that case you should get a warning that "CASCADE is not defined".
I believe I found the problem: My models.py file was in the root directory, not in the app directory.
I am little bit comfused. Lets say I have such models.
models.py:
class Company(models.Model):
name = models.CharField(blank=False, null=False)
class Game(models.Model):
developer = models.ForeignKey(Company, on_delete=models.CASCADE)
publishers = models.ManyToManyField(Company)
If I use next code:
current_company = Company.object.get(pk=1)
current_company.game_set.all()
as I understand it return all games of current_company, but what field (developer or publishers) Django used?
But this code wouldn't be valid, for precisely this reason. If you tried to run it, Django would tell you that there was a conflict in the reverse relation.
If you have two relationships pointing to the same model, you need to explicitly set related_name on one of them to avoid this conflict.
I have 2 app inside a django project. I want to import a model from one app to another. But it gives me
NameError: name 'JobGenre' is not defined
when I try to syncdb
In customer.models
from job.models import JobGenre
class Worker(Costumer):
keyword=models.ForeignKey(JobGenre, null=True)
and in job.models
class JobGenre(models.Model):
genre=models.CharField(max_length=40)
if i use
keyword=models.ForeignKey('job.models.JobGenre', null=True)
it gives
Error: One or more models did not validate:
costumer.worker: 'keyword' has a relation with model job.models.JobGenre, which has either not been installed or is abstract.
What should I do in this situation?
keyword=models.ForeignKey('job.models.JobGenre', null=True)
Looks incorrect to me.
Try instead:
keyword.models.ForeignKey('job.JobGenre', null=True)
You don't need to give the full package path to ForeignKey method. Just giving appname.modelclass will work.
keyword=models.ForeignKey('job.JobGenre', null=True)
should work. please refer here.
Using the django-rest-framework is it possible to retrieve content from a related field. So for example I want to create a genre list which contains all projects within it. This is what I have but I keep on getting the error:
'Genre' object has no attribute 'project_set'
models.py
class Genre(models.Model):
name = models.CharField(max_length=100, db_index=True)
class Project(models.Model):
title = models.CharField(max_length=100, unique=True)
genres = models.ManyToManyField(Genre, related_name='genres')
serializers.py
class GenreSerializer(serializers.ModelSerializer):
project_set = serializers.ManyRelatedField()
class Meta:
model = Genre
fields = ('name', 'project_set')
The related name you're using on the Project class is badly named. That related name is how you access the set of projects related to a given genre instance. So you should be using something like related_name='projects'. (As it is you've got it the wrong way around.)
Then make sure that your serializer class matches up with the related name you're using, so in both places project_set should then instead be projects.
(Alternatively you could just remove the related_name='genres' entirely and everything will work as you were expecting, as the default related_name will be 'project_set'.)