I am working on creating a simple contest submission system using django. This is my first real django project. Basically each user can view a list of problems, submit a file, and view a results page.
Each problem can be associated with multiple contests, and different contests can use the same problem. Because of this, both problem and contest have a manyToManyField with each other. This is what is causing my problem.
Here is the initial models.py implementation I am going with:
startfile
from django.db import models
class User(models.Model):
username = models.CharField(max_length=50)
firstname = models.CharField(max_length=50)
lastname = models.CharField(max_length=50)
class Problem(models.Model):
name = models.CharField(max_length=50)
filename = models.CharField(max_length=300)
contests = models.ManyToManyField(Contest)
class Contest(models.Model):
name = models.CharField(max_length=50)
problems = models.ManyToManyField(Problem)
date = models.DateField()
class Submission(models.Model):
user = models.ForeignKey(User)
problem = models.ForeignKey(Problem)
filename = models.CharField(max_length=300)
endfile
Is there a simple way to fix this? Or should I rethink my entire layout? I tried breaking each class into its own django app but I don't think thats how I should do it. The error I get is that Contest can not be found (because it exists lower in the file).
All advice is appreciated!
You don't need a ManyToManyField in both Contest and Problem. Many-to-many fields are already bidirectional. Just put it on one - doesn't matter which.
Djano will automatically create the reverse relation for you, so you only need to create it one end, eg.
class Problem(models.Model):
name = models.CharField(max_length=50)
filename = models.CharField(max_length=300)
contests = models.ManyToManyField(Contest, related_name='problems')
related_name gives you the possibility to assign a name to the reverse relation. Without defining the relation on the Contest model, you can then access eg. a_contest.problems.all()!
Related
In admin add view I would like to able to select dynamically field A_permission from selected A-object while creating new B-object
A(models.Model):
name = models.CharField(primary_key=True, max_length=50)
permission = models.CharField(max_length=50)
B(models.Model):
A_name = models.ForeignKey(A)
A_permissions = models.ManyToManyField(A)
So I have objectA1 and objectA2 for example. While creating object B I should be able to first select one of the A objects, and then just get its permission for selection in field A_permissions
Can someone please point me how to do this? I feel like I tried everything
Further to the comments I made to your question, below is how I would allow selecting multiple permissions from A to one record in B.
In models.py:
class A(models.Model):
name = models.CharField(primary_key=True, max_length=50)
permission = models.CharField(max_length=50)
def __str__(self):
return f"{self.name}: {self.permission}"
class B(models.Model):
A_name = models.ManyToManyField(A)
In admin.py
from .models import A, B
admin.site.register(A)
admin.site.register(B)
Go to admin
You should be able to select multiple Permissions from A in one record for B using shift+click or ctrl+click.
There are many good django tutorials out there. I find the mozilla django tutorial to be quite good.
I have a few apps within my Django project. There are two apps that I am currently working with "Application" and "User" and I have two questions related to models:
Question 1:
I want to design it in such a way so that external users submit their contact form on Application/templates/Application/Apply.html and the info would get added to the database. Internal users would be able to add external users as well but from a different template: User/templates/User/AddNewContact.html
I am able to add a new contact from an internal user's perspective:
User/models.py
class Contact(models.Model):
ContactName = models.CharField(max_length = 250, default='')
ContactResidence = models.CharField(max_length = 250, default='')
Tel = models.CharField(max_length = 250, default='')
def get_absolute_url(self):
return reverse('User:ContactDetails', kwargs={'pk': self.pk}
)
def __str__(self):
return self.ContactName
class Locations(models.Model):
contact = models.ForeignKey(Contact, on_delete=models.CASCADE)
Country = models.CharField(max_length=250, default='')
def __str__(self):
return self.Country
I was going to just copy this model and paste it into Application/models.py but there are two problems:
1) I don't want external users to be directed to URL: User:ContactDetails and technically, it is not going to work out because I will build the authentication later on.
2) I feel that by copying and pasting I am breaking the 'don't repeat yourself" rule.
Should I connect two models using the foreign keys? What are the best practices in this case?
Question 2
Am I working with one-to-many relationship according to the model provided? I want to have one contact with his personal info (tel/email/address) and a number of branch locations across the world associated with that contact.
To be used a relationship one to many, you can be doing as after:
On models of father app (father table):
class Department(models.Model):
dept_id = models.AutoField(primary_key=True)
On models of child app (child table):
from appname.models import Department
class Office(models.Model):
office_id = models.AutoField(primary_key=True)
name = models.CharField(max_length=200)
dept = models.ForeignKey(Department, on_delete=models.CASCADE)
It helped me.
Question 1: Well, you don't need to copy paste the model. You can use models from other django apps anytime, just need to import it. Basically what you should do is, instead of linking the url directly to the template in the Applications app, you should connect it to a view. In the view file you can import the models from User.models import *, and use them normally.
Question 2: As far as I understand the question your structure provides what you want: one contact (with personal info) associated with several countries. Except that you should replace Agent by Contact in contact = models.ForeignKey(Agent, on_delete=models.CASCADE)
Question 1: Note that the 'get_absolute_url' method is only called if you don't provide a success url in your view. If you are using a CreateView or FormView you can specify the success url by overriding the get_success_url method, for example:
class ContactCreateView(CreateView):
model = Contact
fields = ['ContactName', 'ContactResidence', 'Tel']
def get_success_url(self):
if not self.request.user.internal: # e.g. internal is a User bool field
return HttpResponseRedirect('some/external/url/')
return super().get_success_url() # call get_absolute_url model method.
The DRY principle is respected.
Question 2: Yes, the question you need to ask yourself is 'does a model instance (In this case Contact) have many instances of another model (Location)?' If the answer is yes, then the M2M field should go into your Contact model. See the django docs explaining the pizza/toppings example.
The apps should be in the same project and you can import one model as:
import appName.models or
from appName.models import ClassName
In app2 models you can use foreignKey or manyTomany after importing the class:
from appsName.models import ClassName
class Person(models.Model):
con = ForeignKey(ClassName)
I am trying to create the following models. There is a ManyToMany relation from Entry to AUTH_USER_MODEL via the EntryLike intermediate model.
class BaseType(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
creation_time = models.DateTimeField(auto_now_add=True)
last_update_time = models.DateTimeField(auto_now=True)
class Meta:
abstract = True
class Title(BaseType):
text = models.CharField(max_length=100)
description = models.TextField()
class EntryLike(BaseType):
entry = models.ForeignKey(Entry)
user = models.ForeignKey(settings.AUTH_USER_MODEL)
class Entry(BaseType):
title = models.ForeignKey(Title, on_delete=models.PROTECT)
text = models.TextField()
user = models.ForeignKey(settings.AUTH_USER_MODEL)
liked_by_users = models.ManyToManyField(settings.AUTH_USER_MODEL, through='EntryLike', through_fields=('entry', 'user'))
Running migrations on the above model scheme throws the error: AttributeError:'str' object has no attribute 'meta'.
Any help in resolving this error would be highly appreciated. Am new to Django & Python, but not to Web Development.
The issue is that settings.AUTH_USER_MODEL is almost certainly not a model instance. It's probably a string that constrains the choices another model can make - settings would be a strange place to leave a model definition.
To do a MTM between the user model and your field above you need need to do:
from django.contrib.auth.models import User
class Entry(BaseType):
title = models.ForeignKey(Title, on_delete=models.PROTECT)
text = models.TextField()
user = models.ForeignKey(User)
def __str__(self):
return self.title
I've added the str function so that it gives a more sensible return when you're manipulating it in admin/shell.
I'd also question whether you need the second set of fields (removed here), as you can use select related between the Entry and EntryLike join table, without any duplication of the fields - you can probably go that way, it's just a bit unnecessary.
Lastly, I'd note that the way I'm using it above just uses the default User object that comes with Django - you may wish to customise it. or extend the base class as you've done here with your own models' base class.
(All of this is predicated on AUTH_USER_MODEL not being a model instance - if it is, can you post the model definition from settings.py? )
I've got a two part question regarding Django Admin.
Firstly, I've got a Django model Classified that has a foreign key field from another table Address. On setting data, I've got no issues with any of the fields and all fields get saved correctly.
However, if I want to edit the foreign field in the entry in Classified, it doesn't display the old/existing data in the fields. Instead it shows empty fields in the popup that opens.
How do I get the fields to display the existing data on clicking the + so that I can edit the correct information?
Secondly, I'm sure I've seen search fields in Django Admin. Am I mistaken? Is there a way for me to implement search in the admin panel? I have over 2 million records which need to be updated deleted from time to time. It's very cumbersome to manually go through all the pages in the admin and delete or edit those.
Adding Model Code:
Classified
class Classified(models.Model):
id = models.AutoField(primary_key=True)
name = models.CharField(max_length=256)
contact_person = models.CharField(max_length=300, blank=True)
email = models.CharField(max_length=100, blank=True)
address = models.ForeignKey(Address)
subcategory = models.ForeignKey(Subcategory)
Address
class Address(models.Model):
id = models.AutoField(primary_key=True)
build_add = models.CharField(max_length=255)
street_add = models.CharField(max_length=255)
area = models.CharField(max_length=255)
city = models.ForeignKey(Cities)
The + means just that - add a new instance of the related object and relate the object you're editing to that. Because you're adding a new object it will be blank to start. If you want to be able to edit existing related objects from another object's admin you need to use inlines.
In your app's admin.py have something like:
from django.contrib import admin
from yourapp.models import Address, Classified
class AddressInline(admin.TabularInline):
model = Address
class ClassifiedAdmin(admin.ModelAdmin):
inlines = [AddressInline,]
admin.site.register(Classified, ClassifiedAdmin)
Adding search from there is really easy.
...
class ClassifiedAdmin(admin.ModelAdmin):
inlines = [AddressInline,]
search_fields = [
'field_you_want_to_search',
'another_field',
'address__field_on_relation',
]
...
Note the double underscore in that last one. That means you can search based on values in related objects' fields.
EDIT: This answer is right in that your foreignkey relationship is the wrong way round to do it this way - with the models shown in your question Classified would be the inline and Address the primary model.
I have just added a new field to one of my models, I have deleted and recreated my database, but when I enter info into the new field, nothing appears to have saved for that field, but the others have.
The field looks like this
class Author(models.Model):
display_name = models.CharField(unique=True,max_length=30)
first_name = models.CharField(max_length=15)
phone = models.CharField(max_length=15, blank=True)
twitter_handle = models.CharField(max_length=20, blank=True)
And I have included it into the fields list in forms.py
class AuthorForm(ModelForm):
class Meta:
model = Author
fields = ['display_name','first_name','twitter_handle','phone']
Any ideas what could be causing this?
Any help appreciated
The code looks fine. Can you provide the rest of your code?
Some databases require that you define a primary_key - depends on your other PKs in the model
Try adding primary_key=True to your display_name field and see if it helps
FIXED
Due to a complex interaction between two forms that are submitted at the same time with various validation constraints, I manually populate the models from the forms in a views function, and I had forgotten to add the twitter_hanle to this, oops sorry, hopefully this will help if someone makes the same oversight.