I have my model Room as follows:
eid = models.CharField(max_length=64, unique=True)
name = models.CharField(max_length=25)
I want to create another field user where user is a foreign key. Is to possible to create a field where multiple values can be added to a single row? For example: there are 3 users: user1,user2,user3.
Now, I want a row to look like:
{'eid':1,'name':'room1','user':[user1,user2,user3]}
Is the above scenario possible or do I need to create separate rows for each user?
Note: A room model can have multiple users, but a user cannot be part of multiple rooms.
If you want to have multiple foreign keys, you can use ManyToManyField. When you convert it to JSON, it will display as array, just like you wanted.
It looks like a classical many-to-many relationship. As the Django docs say for that case, you could have your model Room as something like this:
eid = models.CharField(max_length=64, unique=True)
name = models.CharField(max_length=25)
users = models.ManyToManyField(User)
EDIT: since the OP has mentioned in a comment that one user must have only one room, but that a room may have many users, then their User model must have a ForeignKey field, as it is a one-to-many relationship:
room = models.ForeignKey(Room, on_delete=models.CASCADE)
Possible values for the on_delete field may be checked in the docs.
Related
I have a Users table which is FK to a table called Post. How can I get only the last Post that the user registered? The intention is to return a list of users with the last registered post, but when obtaining the users, if the user has 3 posts, the user is repeated 3 times. I'm interested in only having the user once. Is there an alternative that is not unique?
class User(models.Model):
name = models.CharField(max_length=50)
class Post(models.Model):
title = models.CharField(max_length=50)
user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='posts', related_query_name='posts')
created = models.DateTimeField(default=timezone.now)
class Meta:
get_latest_by = 'created'
ordering = ['-created']`
I already tried with selected_related and prefetch_related, I keep getting multiple user registrations when they have multiple Posts.
user = User.objects.select_related('posts').all().values_list('id', 'name', 'posts__title', 'posts__created')
This does give me the answer I want, but when I change the created field to sort by date, I don't get the newest record, I always get the oldest.
user = User.objects.select_related('posts').all().values_list('id', 'name', 'posts__title', 'posts__created').distinct('id')
I'm trying to do it without resorting to doing a record-by-record for and getting the most recent Post. I know that this is an alternative but I'm trying to find a way to do it directly with the Django ORM, since there are thousands of records and a for is less than optimal.
In that case your Django ORM query would first filter posts by user then order by created in descending order and get the first element of the queryset.
last_user_post = Post.objects.filter(user__id=1).order_by('-created').first()
Alternatively, you can use an user instance:
user = User.objects.get(id=1)
last_user_post = Post.objects.filter(user=user).order_by('-created').first()
I want my id field to be unique per each customer field. Just like the option unique_for_date from Django (https://docs.djangoproject.com/en/1.11/ref/models/fields/#unique) but in this case, not date but customer.
class Sample(NGObject):
id = models.CharField(max_length=128, null=True, blank=False)
customer = models.ForeignKey(Customer, related_name="blood_samples", on_delete=models.SET(get_default_customer))
I believe this should be done, before the save() method?
When a User writes the wrong ID (that already exists) I would also like to present the information in the Admin Form just like it would for normal unique error.
class Meta:
unique_together = ('sample_id', 'customer',)
This has done the trick :)
In my primary class model Deals, I have certain fields as description, price, date_created etc. I now have to add some fields having sub-fields to it. For eg, I'm trying to add an age field to Deals. This age field further has subfields (like score_for_kid, score_for_baby, score_for_old etc), and I want to edit these scores from the admin.
Here is my models.py:
class Deals(models.Model):
description = models.TextField()
price = models.DecimalField(max_digits=7, decimal_places=2)
url = models.URLField(verify_exists=False)
currency = models.CharField(max_length=3)
created_date = models.DateField(auto_now_add=True)
kid_score = models.IntegerField(max_length=2,default=0)
teenager_score = models.IntegerField(max_length=2,default=0)
youth_score = models.IntegerField(max_length=2,default=0)
old_score = models.IntegerField(max_length=2,default=0)
I don't want to store all these sub fields (around 20-25 in 4 different fields) in the model, instead an age field connected to these subfields. Would a ManyToManyField work for this?
The underlying requirement is that when a user selects a subfield (say kids) on the browser, all the objects having higher kid scores are displayed.
I'm very new to Django and any help on this would be great. Thanks.
If I understand your question properly ou need to use ForeignKey fields.
class Deals(models.Model):
description = models.TextField()
price = models.DecimalField(max_digits=7, decimal_places=2)
#...
age = models.ForeignKey(Age)
class Age(models.Model):
kid_score = models.IntegerField(max_length=2,default=0)
teenager_score = models.IntegerField(max_length=2,default=0)
#...
Have a good read of the docs on Models. You might also find it useful to do some reading on relational databases / basic sql.
When you come to edit your objects in the django admin, you'll probably want to use an InlineModelAdmin class.
UPDATE
re-reading your question, it sounds like you might simply want to show / hide these additional fields on the main Deal model. If this is the case then you want to use fieldsets in the admin, with a class 'collapse'. There's an example in the docs.
If you want each Deal record to have multiple kid_score's associated with it then you want a foreign key. If each Deal can only have one kid_score then you need to keep the kid_score (and other) fields in the main model (if this is confusing then definitely do some reading on sql / relational databases).
In my Django app I allow users to create collections of movies by category. This is represented using 3 models, Movie, Collection, and Addition (the Addition model stores movie, collection, and user instances). Simplified versions of all three models are below.
class Movie(models.Model):
name = models.CharField(max_length=64)
class Collection(models.Model):
name = models.CharField(max_length=64)
user = models.ForeignKey(User)
class Addition(models.Model):
user = models.ForeignKey(User)
movie = models.ForeignKey(Movie)
collection = models.ForeignKey(Collection)
So for example a user could create a collection called "80's movies", and add the movie "Indiana Jones" to their collection.
My question is: how do I display a distinct list of movies based on a set of query filters? Right now I am getting a bunch of duplicates for those movies that have been added to more than one collection. I would normally use distinct() to get distinct objects, but in this case I need distinct movies rather than distinct additions, but I need to query the Addition model because I want to allow the user to view movies added by their friends.
Am I setting up my models in an optimal way? Any advice/help would be much appreciated.
Thanks!
First. I don't think you need Addition model here. You try to create many-to-many relation, but there's documented way of doing this:
class Movie(models.Model):
name = models.CharField(max_length=64)
class Collection(models.Model):
name = models.CharField(max_length=64)
user = models.ForeignKey(User)
movies = models.ManyToManyField('Movie', blank=True, null=True)
Second. The documentation says: "To refer to a "reverse" relationship, just use the lowercase name of the model".
So the answer is (for the setup above):
Movie.objects.filter(collection__user=user).distinct()
I want to create an expense tracking application, where each user can enter expenses and classify them into his own categories. Here is the model definition that I use:
from django.db import models
from django.contrib.auth.models import User
class Category(models.Model):
user = models.ForeignKey(User, related_name="my_categories")
name = models.CharField(max_length=50)
class Expense(models.Model):
date = models.DateField()
amount = models.IntegerField()
description = models.TextField()
category = models.ForeignKey(Category)
user = models.ForeignKey(User)
Each category will have to be associated with a user so that we can display each user his own categories to choose while entering the expense. For similar reasons, each expense record should be associated with a user. But in definition of Expense, we are having 2 references to the User models, one directly through 'user' field and another through the 'category' field which has a user reference.
I believe that multiple references like this is a bad thing. Is there a better way to model this? I understand that we can find out the user from the category reference, but it seems a roundabout way of doing it.
Although your db is not 100% normalized, in your case, I do not believe the second reference is redundant. Both 'an expense' and 'a category' are well defined entities, which belong to a user. If you will later want to change your foreign key to allow a null category or to a ManyToManyField, you will notice immediatly that both user fields are required. Lookups by user are also much easier for the db and developer when the column is there.