I have two tables called User and Courses and I want to show the relationship between them my implementing a many-to-many relationship model. I want to implement 3 model classes in total as so:
# user/model.py
from django.db import models
from django.contrib.auth.models import AbstractUser
class User(AbstractUser):
is_status = models.BooleanField(default=False)
is_newbie = models.BooleanField(default=False)
#courses/model.py
from django.db import models
from register.models import User
class Courses(models.Model):
course_name = models.CharField(max_length=100, null = False)
class StatusHasCourse(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
course = models.ForeignKey(Courses, on_delete=models.CASCADE)
How do I implement this so only the relationship between User that have is_status = True are only accessed in the StatusHasCourse model?
You can use the limit_choices_to=… parameter [Django-doc] to specify how to limit the choices. So in this specific case, we can make use of a Q-object [Django-doc] that specifies is_status=True:
from django.db.models import Q
class StatusHasCourse(models.Model):
user = models.ForeignKey(
User,
on_delete=models.CASCADE,
limit_choices_to=Q(is_status=True)
)
course = models.ForeignKey(Courses, on_delete=models.CASCADE)
Related
I would like to execute a single query in Django which retrieves related data, by foreign key, in multiple tables. At present I have to run a query on each table e.g. (House, Furniture, People) using the House number as a filter.
In SQL I can do this in one query like this:
SELECT house.number, house.number_of_rooms, furniture.type, people.name
FROM (house INNER JOIN furniture ON house.number = furniture.house_number)
INNER JOIN people ON house.number = people.house_number
WHERE (((house.number)="21"));
Can this be done in Django?
See example models below:
class House(models.Model):
number = models.CharField('House Number', max_length=10, blank=True, unique=True, primary_key=True)
number_of_rooms = models.IntegerField(default=1, null=True)
class Furniture(models.Model):
house_number = models.ForeignKey(House, on_delete=models.CASCADE, null=True)
type = models.CharField('Furniture Type', max_length=50)
class People(models.Model):
house_number = models.ForeignKey(House, on_delete=models.CASCADE, null=True)
first_name = models.CharField('First Name', max_length=50)
In your models add related_name arguments for foreign keys, so that you can retrieve the objects related to the House() instance.
class Furniture(models.Model):
house_number = models.ForeignKey(House, related_name='house_furniture', on_delete=models.CASCADE, null=True)
type = models.CharField('Furniture Type', max_length=50)
class People(models.Model):
house_number = models.ForeignKey(House, related_name='house_people', on_delete=models.CASCADE, null=True)
first_name = models.CharField('First Name', max_length=50)
Then run the migration using following commands.
python manage.py makemigrations
python manage.py migrate
Then create a new serializers.py module in the same app.
#import models Furniture, People, house
from rest_framework import serializers
class FurnitureSerializer(serializer.ModelSerializer):
class Meta:
model = Furniture
fields = ['type'] # if you want all the fields of model than user '__all__'.
class PeopleSerializer(serializer.ModelSerializer):
class Meta:
model = People
fields = ['first_name'] # if you want all the fields of model than user '__all__'.
class HouseSerializer(serializer.ModelSerializer):
house_furniture = FurnitureSerializer(many=True)
house_people = PeopleSerializer(many=True)
class Meta:
model = Furniture
fields = ['number', 'number_of_rooms', 'house_furniture', 'house_people']
Now, in your views.py you can simply query on model House and serializer the result with HouseSerializer().
#import models from models.py
#import serializer from serializers.py
from rest_framework.views import APIView
from rest_framework.response import Response
from rest_framework import status
from rest_framework.generics import ListAPIView
class ListHouseView(ListAPIView):
serializer_class = HouseSerializer
queryset = House.objects.filter() #here you can apply filters on the fields of house model and user using related_name you can filter on other related models as well.
Now, simply call ad this in your app's urls.py
url_pattern = [
path('list-house/', ListHouseView.as_view()),
]
Make sure that have a path in your project's urls.py to reach this app's urls.py.
The usual Django way of dealing with this is Queryset.prefetch_related() and iterating through Python (unless you're using Postgres, which has its own solution of ArrayAgg). Given your models, it'll cost three queries, but you won't have to deal with de-normalized row results.
h = House.objects.prefetch_related('furniture_set', 'people_set').get(number='21')
for furniture in house.furniture_set.all():
print(furniture)
for person in house.people_set.all():
print(people)
prefetch_related() caches the results and does the "joining" in Python once the queryset is evaluated, so iterating through the reverse relationships won't incur additional queries, and you're free to structure/serialize the data however you like. The raw SQL from this is something like:
SELECT house.number, house.number_of_rooms FROM house WHERE house.number = '1'
SELECT furniture.id, furniture.house_number_id, furniture.type FROM furniture WHERE furniture.house_number_id IN ('1')
SELECT people.id, people.house_number_id, people.first_name FROM people WHERE people.house_number_id IN ('1')
But Django does that behind-the-scenes so that you can just deal with a model instance in Python.
I've just set up the whole import-export thing and I just can't make it export a field from another model, using the foreign key.
models.py
from django.db import models
from django.contrib.auth.models import User
from datetime import date
from .validators import validate_file_size
# Create your models here.
class CORMeserii(models.Model):
CodCOR = models.CharField(max_length=25, primary_key=True, unique=True)
MeserieCor = models.CharField(max_length=50, unique=True)
def __str__(self):
return str(self.CodCOR + " - " + self.MeserieCor)
class Meta:
verbose_name_plural = "CORuri"
class Oferta(models.Model):
solicitant = models.ForeignKey(User, on_delete=models.CASCADE)
cor = models.ForeignKey(CORMeserii, on_delete=models.CASCADE)
dataSolicitare = models.DateField(default=date.today)
locuri = models.IntegerField()
agentEconomic = models.CharField(max_length=50)
adresa = models.CharField(max_length=150)
dataExpirare = models.DateField()
experientaSolicitata = models.CharField(max_length=200)
studiiSolicitate = models.CharField(max_length=200)
judet = models.CharField(max_length=20)
localitate = models.CharField(max_length=25)
telefon = models.CharField(max_length=12)
emailContact = models.EmailField(max_length=40)
rezolvata = models.BooleanField(default=False)
def __str__(self):
return str(self.cor)
admin.py
from django.contrib import admin
from .models import Oferta, CORMeserii
from import_export import resources
from import_export.admin import ImportExportMixin, ImportExportModelAdmin
import tablib
# Register your models here.
class CorImEx(resources.ModelResource):
class Meta:
model = CORMeserii
class CorAdmin(ImportExportMixin, admin.ModelAdmin):
list_display = ('CodCOR', 'MeserieCor')
resource_class = CorImEx
class CorImExAdmin(ImportExportModelAdmin):
resource_class = CorImEx
class OferteImEx(resources.ModelResource):
class Meta:
model = Oferta
fields = ('id', 'solicitant', 'cor', 'oferta.cor.MeserieCor')
class OfertaAdmin(ImportExportMixin, admin.ModelAdmin):
list_display = ('id', 'solicitant', 'dataExpirare', 'dataSolicitare')
resource_class = OferteImEx
class OferteImExAdmin(ImportExportModelAdmin):
resource_class = OferteImEx
admin.site.register(Oferta, OfertaAdmin)
admin.site.register(CORMeserii, CorAdmin)
You can see it in the OferteImEx class - the field 'oferta.cor.MeserieCor'.
I want to export the MeserieCor field from the model CORMeserii - but I can't figure it out.
I tried with: 'oferta.cor.MeserieCor',
cor.MeserieCor', 'MeserieCor' (even though the last 2 ones don't make sense to me at all).
Is there any way to export that field somehow, even though it is from another model? (I'm pretty sure there is but I can't figure it out)
Thanks.
In Django you use double underscore (__) to follow relationship in lookups. It's in the documentation:
Django offers a powerful and intuitive way to “follow” relationships in lookups, taking care of the SQL JOINs for you automatically, behind the scenes. To span a relationship, just use the field name of related fields across models, separated by double underscores, until you get to the field you want.
Link: Lookups that span relationship
There is even an example in the django import export documentation how to follow relationship:
When defining ModelResource fields it is possible to follow model relationships:
class BookResource(resources.ModelResource):
class Meta:
model = Book
fields = ('author__name',)
Source: https://django-import-export.readthedocs.io/en/latest/getting_started.html#customize-resource-options
I want to add a department field on my User model. I am using sql server as my db. I did the following in models.py
class Employee(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE, db_column='user')
department = models.CharField(max_length=20, blank=True)
class Meta:
db_table = 'Employee'
Then, using stored procedure I can fill all the fields of User easily, but when I want to fill the extra field department, I get the error
RelatedObjectDoesNotExist at /fetched
User has no employee.
in views.py, where I retrieve the data from procedure:
q = User(id=result_set[i][0], username=result_set[i][1], is_staff=False,
first_name=result_set[i][4], last_name=result_set[i][3], email=result_set[i][8])
q.set_password(result_set[i][2])
q.employee.department = 'something'
q.save()
You can extend the AbstractUser to your model
In models.py
from django.contrib.auth.models import AbstractUser
class Employee(AbstractUser):
department = models.CharField(max_length=20, blank=True)
I have the following models
from django.contrib.auth.models import User
User = settings.AUTH_USER_MODEL
class UserProfile(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE, related_name='profile')
class Tutor(UserProfile):
# tutor_fields here
From User object how can I access Tutor? is it with user.profile?
user.profile.select_related('tutor') does not seem to work.
OneToOneField work like ForeignKey except unique=True and you don't need to specify the related_name (you can specify if you want to change it).
For you example:
from django.contrib.auth.models import User
User = settings.AUTH_USER_MODEL
class UserProfile(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE, related_name='profile')
class Tutor(UserProfile):
user = models.ForeignKey(UserProfile, on_delete=models.CASCADE, related_name='tutor')
details = models.CharField(max_length=100)
NB: Use a ForeignKey if you want/need one Tutor for many UserProfile, else if you want one (and only one) Tutor for one UserProfile
And you can access to the Tutor bu UserProfile by UserProfile.tutor.details.
As described in the django docs, you should be able to access it with user.user_profile.
I am defining some models for an inventory / work order application I am developing and I've run into a slight sticking point.
Here are some of the models that I'm currently having some difficulty with.
#models.py
from django.db import models
class Staff(models.Model):
ROLE = (
('M', 'Mechanic'),
('W', 'Warehouse'),
)
first_name = models.CharField(max_length=25)
last_name = models.CharField(max_length=25)
staff_role = models.CharField(max_length=1, choices=ROLE)
class WorkOrder(models.Model):
item_number = models.ForeignKey(Item)
date_started = models.DateField()
date_ended = models.DateField()
mechanic = models.ForeignKey(Staff)
What I would like is for a work order to only be associated with a staff member whose role is set as "Mechanic". Is there a way to restrict this within the model specification based on the models that I have here, or should I deal with this downstream when I set up the views and the forms?
Use the limit_choices_to parameter to ForeignKey:
mechanic = models.ForeignKey(Staff, limit_choices_to={'staff_role': 'M'})