I have the following models:
class UserPost(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
post = models.ForeignKey(Post, on_delete=models.CASCADE)
created = models.DateTimeField(auto_now_add=True)
class User(AbstractUser):
MALE = 'M'
FEMALE = 'F'
GENDER_CHOICES = (
(MALE, 'Male'),
(FEMALE, 'Female')
)
posts = models.ManyToManyField(Post, through='UserPost')
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
class Post(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
title = models.CharField(max_length=100)
content = models.TextField()
status = models.CharField(max_length=100)
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
When I run python manage.py makemigrations, it raises the following error:
users.User.posts: (fields.E303) Reverse query name for 'User.posts' clashes with field name 'Post.user'.
HINT: Rename field 'Post.user', or add/change a related_name argument to the definition for field 'User.posts'.
There is a many-to-many relationship between User and Post models. Each user can like many posts and each post can be liked by many users.
There is also a many-to-one relationship between User and Post models. Each user can write many posts and each post can be written by only one user.
Shouldn't reverse query name for 'User.posts' be user_set by default. If so, why is this name clashing with field name 'Post.user'? Can someone explain the meaning of this error? Thanks.
Do you need the UserPost model? It looks to have all the same fields as Post, and if you're after efficient querying, Django automatically creates database indexes on foreign keys. Here's a simple setup that should work pretty well:
class User(AbstractUser):
# Your fields go here, but you might not need the posts field
class Post(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='posts')
This would let you do a user.posts.all() to get all of the Post instances that belong to that user.
Related
I have just started with making a similar site to Pinterest and the site has follower/target system that I have barely any understanding of. So far, my models.py code is below:
from django.db import models
class User(models.Model):
username = models.CharField(max_length=45, null=True)
email = models.CharField(max_length=200, null=True)
password = models.CharField(max_length=200)
nickname = models.CharField(max_length=45, null=True)
target = models.ManyToManyField(self, through='Follow')
follower = models.ManyToManyField(self, through='Follow')
class Meta:
db_table = 'users'
class Follow(models.Model):
follower = models.ForeignKey(User, on_delete=models.CASCADE, related_name='targets')
target = models.ForeignKey(User, on_delete=models.CASCADE, related_name='followers')
class Meta:
db_table = 'follows'
This code was made with reference to another StackOverflow thread
Django models: database design for user and follower
However, I am having trouble understanding how using "related_name='targets' in 'follower' and "related_name='followers'" in 'target' where I can't see any 'targets'(plural) or 'followers'(plural) in other areas of models.py
Should I get rid of that related_name, since there is no such table called "followers" or "targets"? And if you spot major errors in my code or logic, can you tell me? Thanks!
Should I get rid of that related_name, since there is no such table called followers or targets.
There is never a table named followers or targets. The related_name [Django-doc] is a conceptual relation Django makes to the other model (in this case User). It means that for a User object myuser, you can access the Follow objects that refer to that user through target for example with myuser.followers.all(), so:
Follow.objects.filter(target=myuser)
is equivalent to:
myuser.followers.all()
The default of a related_name is modelname_set, so here that would be follow_set. But if you remove both related_names, then that would result in a name conflict, since one can not add two relations follow_set to the User model (and each having a different semantical value).
if you spot major errors in my code or logic, can you tell me?
The problem is that since ManyToManyFields refer to 'self' (it should be 'self' as string literal), it is ambigous what the "source" and what the target will be, furthermore Django will assume that the relation is symmetrical [Django-doc], which is not the case. You should specify what the source and target foreign keys are, you can do that with the through_fields=… parameter [Django-doc]. It furthermore is better to simply define the related_name of the ManyToManyField in reverse, to avoid duplicated logic.
from django.db import models
class User(models.Model):
username = models.CharField(max_length=45, unique=True)
email = models.CharField(max_length=200)
password = models.CharField(max_length=200)
nickname = models.CharField(max_length=45)
follows = models.ManyToManyField(
'self',
through='Follow',
symmetrical=False,
related_name='followed_by',
through_fields=('follower', 'target')
)
class Meta:
db_table = 'users'
class Follow(models.Model):
follower = models.ForeignKey(
User,
on_delete=models.CASCADE,
related_name='targets'
)
target = models.ForeignKey(
User,
on_delete=models.CASCADE,
related_name='followers'
)
class Meta:
db_table = 'follows'
Here a User object myuser can thus access myuser.follows.all() to access all the users that they follow, myuser.followed_by.all() is the set of Users that follow myuser. myuser.targets.all() is the set of Follow objects that he is following, and myuser.followers.all() is the set of Follow objects that are following that user.
I have a model:
class Product(models.Model):
title = models.CharField(max_length=200)
url = models.URLField()
pub_date = models.DateTimeField()
votes_total = models.IntegerField(default=1)
image = models.ImageField(upload_to='images/')
icon = models.ImageField(upload_to='images/')
body = models.TextField()
hunter = models.ForeignKey(User, on_delete=models.CASCADE)
Now I'd like to add a functionality of upvoters to know on what products user has already voted. I need this to allow users vote on the one product only once.
Again, to clarify - user can vote on several products but only once on each.
So the relation is one product - many users (upvoters).
I tried to add the next field but cannot make a migration even if default field is provided. Also I tried to clear the database but again cannot make it work.
upvoters = models.ForeignKey(User, on_delete=models.CASCADE, related_name='upvoted')
I suppose it works the next way:
Field to determine upvoted products.
To check if user has been upvoted on product, call: User.upvoted.filter(id=product.id).count() == 1
This means that user has already upvoted on this product.
What's wrong? What should I change to make it work?
You will have to use ManyToMany, but you can use a custom through model to restrict the product/vote combinations.
To Product class, add:
voters = models.ManyToManyField(User, through='ProductVote', related_name='product_voters')
Then add the custom through model:
class ProductVote(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
product = models.ForeignKey(Vote, on_delete=models.CASCADE)
class Meta:
unique_together = ['user', 'product']
If you try to add a vote for the same user/product combination, an IntegrityError will be raised.
I have a model named UserProfile and a model PersonalInformation. I would like to fetch all the data of PersonalInformation using UserProfile model when the user is logged into the webiste but i have a foreign key refernce in the PersonalInformation model with the UserProfile model so how do i fetch the personal information using UserProfile model?
User Profile Model :
class UserProfile(models.Model):
"""Represents a user's model inside our system"""
email = models.EmailField(max_length=255, unique=True)
name = models.CharField(max_length=255)
profile_picture = models.ImageField(upload_to='photos/%y/%m/%d/')
is_active = models.BooleanField(default=True)
is_staff = models.BooleanField(default=False)
highest_degree_earned = models.CharField(max_length=255, blank=False)
college_name = models.CharField(max_length=255, blank=False)
graduation_year = models.IntegerField(default=2020, blank=False)
Personal Information Model :
class PersonalInformation(models.Model):
"""Represents a user's personal Infromation inside our system"""
user = models.ForeignKey(UserProfile, on_delete=models.CASCADE)
mobile = models.CharField(max_length=10 ,blank=True)
bio = models.TextField(max_length=200, blank=True)
college_university = models.CharField(max_length=100, blank=False)
course = models.CharField(max_length=100, blank=False)
First of all, in the code, you are showing you have the names of the models wrong. The UserProfile model name is set as PersonalInformation, change it or the migrations won't work (it's not accepted on the database no matter which one you're using).
Referent to the question you're asking, to fetch the related instance of PersonalInformation of a certain UserProfile instance you should just query the next:
user = UserProfile.objects.get(id='') #Introduce the id of the user you want to fetch its personal information.
user.personalinformation_set.all() # This will return you a QuerySet with all the related instances of PersonalInformation class.
user.personalinformation_set.get(id='') #To get a specific one or you may use a filter to get a filtered QS.
If you want, you can use the related_name attribute for ForeignKey class in order to set a different name from personalinformation_set.
I recommend you too to read the Django documentation, it's really well explained and clear I think:
https://docs.djangoproject.com/en/2.2/topics/db/examples/many_to_one/
As I've seen in a comment, you may also think to use a OneToOne relation instead of ForeignKey if you only expect one instance of PersonalInformation per User. The documentation is at:
https://docs.djangoproject.com/en/2.2/topics/db/examples/one_to_one/
I have the below in my models.py file:
class Film(models.Model):
title = models.CharField(max_length=200)
director = models.CharField(max_length=200)
description = models.CharField(max_length=200)
pub_date = models.DateField('date published')
class Comment(models.Model):
film = models.ForeignKey(Film, on_delete=models.CASCADE)
body = models.CharField(max_length=200)
When I logged into Django admin I added some films, and then added some comments, selecting which film object the comment related to. I then created a couple of users via the admin panel also.
I would like my relationships to be:
Film can have many comments / Comments belong to film
User can have many comments / Comments belong to user
I think, like with comments and films, I just need to define user as a foreign key to comment. I am struggling to do this. I am working through the Django tutorials but I can't see the tutorials covering how I can link other tables to the user.
I thought I would be able to do something like this:
user = models.ForeignKey(User, on_delete=models.CASCADE)
While importing User like this:
from django.contrib.auth.models import User
The result at the moment is if I keep user = models.ForeignKey(User, on_delete=models.CASCADE) I get err_connection_refused
Maybe have you changed your default user model in the settings?
Instead of using User directly with the the Foreign key, you should use user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE) in your Comment Model, as follow
class Comment(models.Model):
film = models.ForeignKey(Film, on_delete=models.CASCADE)
body = models.CharField(max_length=200)
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
You need to apply migrations to be able to add user to Comment,
python manage.py makemigrations
python manage.py migrate
if at the moment that you are applying migrations, shell shows a message telling You are trying to add a non-nullable field 'user' to comment without a default
You have 2 Options
Skip migrations and add a default value to the field in the models or set the attribute as nullable, whatever else that you need
ie
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, null=True, blank=True)
and apply migrations again
Or select a default value to the new field, should be an id of an existing user in databse
This is because django should populate existing records in database, if exist
Use "settings.AUTH_USER_MODEL".
So, import "settings" from "django.conf", then use "settings.AUTH_USER_MODEL" as shown below:
from django.db import models
from django.conf import settings # Here
class Comment(models.Model):
film = models.ForeignKey(Film, on_delete=models.CASCADE)
body = models.CharField(max_length=200)
# Here
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
I am trying to build relations with my database tables. Im having a tutorial lesson at the moment with 3 tables. for example (auth_user table, partyEvent table, friends table).
Now a user should be able to create just one partyEvent. Friends can join any number of partyEvent created by the users.
The owner id in the Friends model tells the partyEvent and User 'the friend' belongs to.
I am able to restrict the users to create only one partyEvent. But when i try to register friends to a partyEvent, the owner's id is not sent. Instead the default value in:
owner = models.OneToOneField('auth.User', related_name = 'party', on_delete=models.CASCADE, default='1')
is rather sent. Why is that happening?
models
class PartyEvent(models.Model):
name = models.CharField(max_length=100, blank=False)
location = models.CharField(max_length=100, blank=False)
owner = models.OneToOneField('auth.User', related_name = 'party', on_delete=models.CASCADE, default='1')
class Friends(models.Model):
name = models.CharField(max_length=100, blank=False)
owner = models.ForeignKey('auth.User',related_name = 'friends', on_delete=models.CASCADE, default='1')
serializers
class FriendsSerializer(serializers.HyperlinkedModelSerializer):
owner = serializers.ReadOnlyField(source='owner.id')
class Meta:
model = Friends
fields = ('id','name','owner')
You can set current user by assigning serializers.CurrentUserDefault() as your serializer field default. Here is an example from the doc:
owner = serializers.HiddenField(
default=serializers.CurrentUserDefault()
)