the idea is that students can send a ping to their teacher if they do not understand something, but first I am trying to get the student, teacher and whatever class they are in relationship
so in my models after a few attempts I have come up with this
Models
from django.db import models
class Student(models.Model):
name = models.CharField(max_length=50)
class Teacher(models.Model):
name = models.CharField(max_length = 70)
class Lecture(models.Model):
name = models.CharField(max_length = 70)
members = models.ManyToManyField(
Student,
through = 'part_of_class',
through_fields = ('lecture', 'student'),
)
lecturers = models.ManyToManyField(
Teacher,
through = 'Teacher_of_class',
through_fields = ('lecture', 'teacher'),
)
class Teacher_of_class(models.Model):
lecture = models.ForeignKey(Lecture)
teacher = models.ForeignKey(Teacher)
class part_of_class(models.Model):
lecture = models.ForeignKey(Lecture)
student = models.ForeignKey(Student)
Question is adding a student field messes up, and Im not even sure this is the right way, it sounds right in my head but I am sure I am missing something, any clues?
I'm not entirely sure that you need explicit intermediary relationships (Teacher_of_class and part_of_class). Instead, you should try utilizing fields within the other models to do what you want. For example, will a lecture generally have more than one teacher, or just one? You could model either of those with a field in Lecture.
Edit: Apologies, I misread your code initially with regards to the fields. My suggestion is to not use an additional relationship class unless you know why you need it.
If you just want to have a lecture that can have multiple students and multiple lecturers, you do not need to have the intermediate models, Django will handle this for you if you don't specify any. I would only use the intermediate tables if you wanted to store something with that relationship.
Also when trying to add your student and teacher objects to the lecture model, be sure to save them.
Your save code should look something like this:
aStudent = Student(name="Taco")
aTeacher = Teacher(name="Burrito")
aStudent.save()
aTeacher.save()
aLecture = Lecture(name="Cooking With Python!")
aLecture.members.add(aStudent)
aLecture.lecturers.add(aTeacher)
aLecture.save()
Hope this helps!
Related
I have two models UserProfile and ChatUser.
ChatUser.models.py
class ChatUser(models.Model):
chat = models.ForeignKey(ChatRoom,on_delete=models.CASCADE)
user = models.ForeignKey(User,on_delete=models.CASCADE)
UserProfile.models.py
class UserProfile(models.Model):
user = models.OneToOneField(User,on_delete=models.CASCADE)
phone_number = models.IntegerField(default=0)
image = models.ImageField(upload_to='profile_image',blank=True,default='prof1.jpeg')
gender = models.CharField(max_length=10)
joined = JSONField(null=True)
ChatRoom.models
class ChatRoom(models.Model):
eid = models.CharField(max_length=64, unique=True)
name = models.CharField(max_length=100)
location = models.CharField(max_length=50)
vehicle = models.CharField(max_length=50)
brand = models.CharField(max_length=50)
max_limit = models.IntegerField()
joined in UserProfile is an array consisting room ids of the chatrooms model. Now when I delete a ChatRoom row, it automatically deletes the Foreign Key referenced ChatUser object since I am using on_delete=models.CASCADE. But how to update the joined in UserProfile model. I want to remove the id of the deleted ChatRoom from UserProfile.joined
I have used the django.db.models.signals to solve the updating part.
#receiver(post_delete,sender=ChatUser)
def update_profile(sender,instance,**kwargs):
id = instance.chat_id
joined = instance.user.userprofile.joined
if id in joined:
joined.remove(id)
model = profiles.models.UserProfile.objects.filter(user_id=instance.user.id).update(joined=joined)
SDRJ and Willem Van OnSem, thank you for your suggestions
#SAI SANTOSH CHIRAG- Please explain this. You have a ChatUser model that adds user_id and chatroom_id. Now, if I need to find out the list of chatrooms a user has joined, I can simply query this model. If I want to find out the total number of users in a specific chatroom then I can still query this table. Why do I need to keep track of joined in UserProfile? And I am basing this on the premise that joined keeps track of chatroom ids that a user has joined.
At any point, if you choose to add a many-to-many field in any of the models then this is my opinion. E.g Let's assume that you add the following in the UserProfile model
chatroom = models.ManytoManyField(Chat)
Imagine as the number of chatrooms the user joins grows, the list becomes larger and larger and I find it inconvenient because I will have this tiny scroll bar with a large list. It's not wrong but I simply stay away from M2M field for this purpose especially if I expect my list to grow as my application scales.
I prefer the ChatUser approach that you used. Yes, I might have repeating rows of user_ids or repeating chatroom_ids but I don't mind. I can live with it. It's still a bit cleaner to me. And this is simply my opinion. Feel free to disagree.
Lastly, I would rename the ChatUser model to ChatRoomUser...Why? Just by the name of it, I can infer it has something to do with two entities Chatroom and User.
I have models with hierarchical relationships:
class School(models.Model):
name = models.CharField()
class Class(models.Model):
school = models.ForeignKey(School)
class Student(models.Model):
class = models.ForeignKey(Class)
And I'd like to retrieve every Student objects related to certain School.
I usually did it like below:
the_school = School.objects.get(name='Springfield Elementary School')
students = Student.objects.filter(class__school=the_school)
But this method needs two models to look up (School and Student) which seems somewhat unnecessary... For me.
So I tried to make a single line query, using Django's built in related manager:
students = School.objects.get(name='...').class_set.student_set.all()
# or
students = School.objects.get(name='...').class_set.all().student_set.all()
...which did not work.
How can I make a query referencing down from given School object?
Or is there any better solution?
You can use class__school__name as filter argument:
students = Student.objects.filter(class__school__name='Springfield Elementary School''Springfield Elementary School')
So, I have the following models:
class Band(models.Model):
name = models.CharField(max_length=50)
class Contract(models.Model):
band = models.ForeignKey(Band)
when = models.DateTimeField(auto_now_add=True)
salary = models.IntegerField()
class Musician(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
instrument = models.CharField(max_length=100)
bands = models.ManyToManyField(Band, through=Contract)
class Album(models.Model):
artist = models.ForeignKey(Musician)
name = models.CharField(max_length=100)
release_date = models.DateField()
num_stars = models.IntegerField()
So, I wanted to expose that on the admin page. So far, so good.
Note that our musicians here keep jumping in and out from bands. Some say one of them even had been on over 2 millions bands in his life-time. I don't know, maybe the bands are Whitesnake, Metallica or something.
How should we do that on the Django Admin Page?
I tried using raw_id_fields and apart the fact I didn't like the effect, it didn't work so well. It took a lot of time to load and it didn't let me add more ids. Weird.
I've used admin.StackedInline with no luck cause it will try to load every contract in a which, well, it's gonna take only 2 thousand years.
When Musician had a direct relation to Band it worked just fine with this library. But now that the relation isn't an straight one. Looks like autocomplete doesn't support it(it was getting slow anyway).
So, with all of this, I ask you lord SO members. What's the best way to do this? Is it autocomplete? Someone must have had to come across this issue!
Thanks in advance.
To avoid loading every bands in your admin page use autocomplete_fields Django doc.
Just use it like that in your admin.py.
autocomplete_fields = ('bands',)
Then no bands will be pulled from DB to front, but you will be able to select it through a Select2 search field and it will be printed as "tags".
I found this solution and hope it will help somebody in the same situation:
I have many to many relations between the Product and Characteristic model.
So, in the admin.py I am setting a form for a Product like the following where catch/get all the Characteristics and make the "prefecth_related" for Characteristic, as well the "select_related" could be done there:
class ProductAdminForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.fields['characteristics'].queryset = Characteristic.objects.prefetch_related('category').all()
I'm trying to wrap my head around how I would structure my database tables in the Django webapp I'm writing. I'm a relative newbie to web development, but this is the very first time I've tried to use a database, so bear with me if it's a stupid question.
The webapp goes through each Oscar the Academy gives out and allows the user to select which of some (varying) number of nominations will win an Oscar. The data from each individual session will be publicly available by going to a url like [url].com/answers/[unique id]. The overall data will also be available on a results page. So I've started writing my models file, and this is what I have so far:
from django.db import models
class Nominee(models.Model):
award = models.CharField(max_length=50)
title = models.CharField(max_length=50)
key = modelsCharField(max_length=50)
subtitle = models.CharField(max_length=50)
numVotes = models.IntegerField()
class Session(models.Model):
id = models.IntegerField() # unique id of visitor
bpictureVote = models.ForeignKey(Nominee, related_name = 'nom')
bactorVote = models.ForeignKey(Nominee, related_name = 'nom')
# ... for each award
I was originally thinking of having
class Award(models.Model):
name = models.CharField(max_length=50)
and at the beginning of Nominee,
award = models.ForeignKey(Award, related_name = 'award')
but I couldn't figure out why that would be better than just having award be a part of the Nominee class.
This is really just a start, because I've gotten a bit stuck. Am I on the right track? Should I be doing this totally differently (as I probably should...)? Any thoughts?
Thanks!
You are on the right track.
You need a separate Award class to avoid having to type in award's name every time you create a Nominee. By having a ForeignKey reference you make sure that you can safely rename your award, add additional information about the award (let's say in the future you decide to give each award a separate page with a description and a list of nominees), you also avoid errors which can happen from having a set of different spellings and typos ("Best Engineer Award" and "Best Engineer award"). It also makes sense - your application operates a set of objects: user sessions, nominees and awards.
Few unrelated notes:
You don't need an explicit Session.id field, django ORM creates it for you.
Property names have to be name_with_underscores, not camelCase.
No spaces around "=" in an arguments list: models.ForeignKey(Nominee, related_name='nom').
4 spaces instead of 2 (unless explicitly otherwise specified).
I am not entirely sure, because you do mention multiple nominees per award (assuming this is something like a poll before the actual nomination) a ManyToMany would be your required relation, in order to use also the additional user data.
But in the case you have implemented this as a specific app for nominations and implemented a custom user model then this would be refactored to something else...
Anyway to your current implementation:
class Nominee(models.Model):
title = models.CharField(max_length=50)
key = modelsCharField(max_length=50)
subtitle = models.CharField(max_length=50)
...
class Award(models.Model):
name = models.CharField(max_length=50)
nominees = models.ManyToManyField(Nominee, through='AwardNominees')
...
class AwardNominees(models.Model):
nominee = models.ForeignKey(Nominee)
award = models.ForeignKey(Award)
user = models.ForeignKey(User)
numVotes = models.IntegerField()
....
So it turned out I was thinking about this entirely wrong. I've now completely changed things, and now it's fully functional (!). But in the spirit of full disclosure, I should say that it definitely may not be the best solution. It sure seems like a good one, though, because it's really simple. Now I have only one model:
class Vote(models.Model):
award = models.CharField(...) # Name of the award
title = models.CharField(...) # Title of the nominee
subtitle = models.CharField(...) # Subtitle of the nominee
uid = models.CharField(...) # A 6 character user ID for future access
When I want to show the results of one user's votes, I can use Django's database tools to filter for a certain uid captured in the URL. When I want to tally the votes, I can use a combination of filters and Django's count() to determine how many votes each nominee had for a certain award. Sounds reasonable enough to me!
I have a social-clique-object.
In each social-clique-object I have a list of friend-objects.
Each friend-object has a relationship-object (full of fun facts like when they met) with each other friend.
Herein I am stuck. How do I properly define my models so that I can query any friend-object to pull up their shared relationship-object?
I do not see this is simply solved with a bidirectional model like this answer since I am dealing with a large and growing list of friend objects (in the linked-to solution they create two different models e.g. friend_a and friend_b).
My current approach was for the Relationship object to look like what is posted below. I would have to add logic in my code to prevent duplicate Relationship objects... but this
class Relationship(models.Model):
social_clique = models.ForeignKey( Social_Clique )
friend_0 = models.ManyToManyField( Friend, related_name='friend_0' )
friend_1 = models.ManyToManyField( Friend, related_name='friend_1' )
I sense I am missing the right keyword to google for to find the ORM design pattern for this problem. Any suggestions on the right description of this problem or how to address this?
It doesn't make sense for either of the friend_x fields to be ManyToManys. The relationship between friends is ManyToMany, but Relationship is itself the intermediary model in the many-to-many relationship (hence the name). So the friend_ fields should be ForeignKeys, and then you additionally define a ManyToMany field from Friend to itself using Relationship as the through model:
class Relationship(models.Model):
social_clique = models.ForeignKey(Social_Clique)
friend_0 = models.ForeignKey(Friend, related_name='friend_0')
friend_1 = models.ForeignKey(Friend, related_name='friend_1')
class Friend(models.Model):
... other fields ...
friends = models.ManyToManyField('Friend', through=Relationship)
Now it's easy to go from two friends (me and my_friend) to their shared relationship:
Relationship.objects.get(friend_0=me, friend_1=my_friend)
or
me.friend_0.filter(friend1=my_friend)
etc. And you can still get all my friends:
me.friends.all()