I have a profile model with a ManyToMany field called that relates to a Stock. In my admin dashboard I'm trying to show the number of watchlists each stock is in. The annotation query I have is:
qs.annotate(watchlist_count=Count('profile__watchlist__symbol'))
But it's returning incorrect results
Here are the models:
class Profile(models.Model):
user = OneToOneField(User, on_delete=models.CASCADE)
watchlist = ManyToManyField(Stock, blank=True)
def __str__(self):
return self.user.email
class Stock(models.Model):
symbol = CharField(max_length=15, unique=True)
name = CharField(max_length=100)
category = CharField(max_length=30, choices=CATEGORY_CHOICES, blank=True)
about = TextField(help_text='About this company')
def __str__(self):
return f'{self.symbol} - {self.name}'
The equivalent SQL query is:
select stock_id, count(stock_id) from api_profile_watchlist group by stock_id;
What is wrong with my annotation query?
You do too much joins. By joining twice over the many-to-many relation, you "blow up" the count.
You can simply count the amount of watchlists with that Stock, with:
from django.db.models import Count
Stock.objects.annotate(
watchlist_count=Count('profile')
)
This works since, by default, the related_query_name=… [Django-doc] has the name of the model (or the related_name if you specified one). So the implicit relation you wrote from Stock to Profile (the reverse one of Profile to Stock in your watchlist relation), is profile (in lowercase). We thus ask Django to count, for a given Stock object, the number of relations to a Profile.
Related
I have the following models:
# Get or create a 'Not selected' category
def get_placeholder_categoy():
category, _ = ListingCategories.objects.get_or_create(category='Not selected')
return category
# Get default's category ID
def get_placeholder_category_id():
return get_placeholder_categoy().id
class ListingCategories(models.Model):
category = models.CharField(max_length=128, unique=True)
def __str__(self):
return f'{self.category}'
class Listing(models.Model):
title = models.CharField(max_length=256)
seller = models.ForeignKey(User, on_delete=models.CASCADE, related_name='listings')
description = models.TextField(max_length=5120, blank=True)
img_url = models.URLField(default='https://media.istockphoto.com/vectors/no-image-available-picture-coming-soon-missing-photo-image-vector-id1379257950?b=1&k=20&m=1379257950&s=170667a&w=0&h=RyBlzT5Jt2U87CNkopCku3Use3c_3bsKS3yj6InGx1I=')
category = models.ForeignKey(ListingCategories, on_delete=models.CASCADE, default=get_placeholder_category_id, related_name='listings')
creation_date = models.DateTimeField()
base_price = models.DecimalField(max_digits=10, decimal_places=2, validators=[
MinValueValidator(0.01),
MaxValueValidator(99999999.99)
])
With these, I have the following form:
class ListingForm(ModelForm):
class Meta:
model = Listing
exclude = ['seller', 'creation_date']
widgets = {
'title': TextInput(attrs=base_html_classes),
'description': Textarea(attrs=base_html_classes),
'img_url': URLInput(attrs=base_html_classes),
'category': Select(attrs=base_html_classes),
'base_price': NumberInput(attrs=base_html_classes)
}
One of the available categories I have is "Not selected", since I want to allow that if at some point a category were to be removed, items can be reassigned to that one, however, when rendering the form, I will do some validation on the view function to prevent it from being submitted if the "not selected" category is sent with the form.
Because of this, I want the HTML form on the template to assign the 'disabled' attribute to the option corresponding to that category, however, I have been searching for a couple of days now without finding anything that I was able to understand to the point where I could try it.
Ideally, another thing I'd like to achieve is to be able to modify the order of the rendered options on the form so that I can move to the top 'not selected' regardless of its primary key within the model.
I am aware I can just create a form instead of a model form, or just modify the template so I manually specify how to render the form itself, but I do feel like there is a simple fix to this either on the model or on the model form that I am just not finding yet.
Thanks in advance!
I would suggest you use (in model definition)
class Listing(models.Model):
..
category = model.ForeignKey(ListingCategories, on_delete=models.SET_NULL, null=True, related_name='listings')
..
and optionally in form definition
class ListingForm(ModelForm):
category = forms.ModelChoiceField(ListingCategories, empty_label='Not Selected')
..
While rendering model form, a required attribute will be automatically added, and in form validating, it is also required. It is only in database validation that the field can be left NULL
I am in a process of creating a Room Booking Management System using Django. I have faced an issue in accessing models.
Here is my Room Model
class Room(models.Model):
name = models.CharField(max_length=30)
date = models.DateField()
defined_check_in_time = models.IntegerField()
defined_check_out_time = models.IntegerField()
booked = models.BooleanField(default = False)
USERNAME_FIELD = 'name'
class Meta:
ordering = ['date', 'defined_check_in_time']
def __str__(self):
return self.name
def is_booked(self):
return self.booked
def set_booked(self):
self.booked = True
Here is my Booking Model
class Booking(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
room = models.ForeignKey(Room, on_delete=models.CASCADE)
def __str__(self):
return f'{self.user} has booked {self.room} from {self.room.defined_check_in_time} to {self.room.defined_check_out_time} on {self.room.date}'
I have linked the User model and Room model in the Booking model using a foreign key when a user books a room. User model is defined in another file. I have not included that model code here.
When a user books a room, the corresponding room object and user object is linked to the booking object. To display the bookings of the user, I need to query the Booking model using a User object.
Here, my question is how i can access user and room object attributes inside the booking object?
To access information within your booking object, you must first select a booking object, whichever way you choose to identify a booking.. maybe by an id. Let's say booking id=100
booking = Booking.objects.get(id=100)
Now to find foreign key info you can just . lookup.
booking_user = booking.user.username
booking_room = booking.room.name
or to find any bookings on rooms booked:
booked_rooms = Booking.objects.filter(room.booked == True)
models.py
class products(models.Model):
name = models.CharField(max_length=100)
sku = models.CharField(max_length=50)
vendor = models.CharField(max_length=50)
brand = models.CharField(max_length=50)
price = models.FloatField()
product_status = models.BooleanField()
quantity = models.IntegerField()
def __str__(self):
return self.name
# categories
class categories(models.Model):
category_name = models.CharField(max_length=50)
parent_id = models.IntegerField()
# product categories
class product_categories(models.Model):
product = models.ForeignKey(products, on_delete=models.CASCADE)
category = models.ForeignKey(categories, on_delete=models.CASCADE)
def __str__(self):
return self.category
I can access 'category' table data(inside django shell) using
data = products.objects.all()
data.values('product_categories__category__category_name')
output: <QuerySet [{'product_categories__category__category_name': 'xxxx'}}]>
If I put this(inside django shell)
data.product_categories.category
output: 'QuerySet' object has no attribute 'product_categories'
How do I get a queryset(can be passed to html) which includes data from "categories" table along with the data of "products" table
There are a couple of issues happening here. First, data is a queryset, which is kind of like a list of objects, even though here there's just one object in the list. What you want is to get an attribute off of the item in the list, so you need something like a data.first() to get to that object before you start dotting into its attributes.
Secondly, the way Django handles reverse FK relationships requires that you refer to the FK by the standard name of, in your case, product_categories_set, OR you set your own related_name attribute on the FK. Something like:
# product categories
class product_categories(models.Model):
product = models.ForeignKey(products, on_delete=models.CASCADE, related_name='product_categories')
category = models.ForeignKey(categories, on_delete=models.CASCADE, related_name='product_categories')
def __str__(self):
return self.category
so that you can refer to your product_categories model from both the product and categories using just data.product_categories.
Thirdly, when accessing a reverse FK relationship, just like in point (1) above, you will get a related manager, from which you can get a queryset of items. Thus, to get the category name, you need to indicate which item you want the category name for. Assuming it's just the first item for everything, it would look something like:
data = products.objects.all()
product_category = data.product_categories.all()
category_name = product_category.category.category_name
Of course once you have more data, you'll not always want to just pick the first item, so you'll need to add filtering logic into the query to make sure you get the item you're looking for.
ETA, I do agree with the comment by Jorge above - a MTM would make this a bit simpler and would, in essence, create your product_categories table for you.
models.py
from django.db import models
class UserGroup(models.Model):
members = models.ManyToManyField(User, related_name='members', through='UserGroupMember')
class UserGroupMember(models.Model):
user = models.ForeignKey(User)
usergroup = models.ForeignKey(UserGroup)
class Cohort(models.Model):
user_groups = models.ManyToManyField(UserGroup)
class Team(models.Model):
cohort = models.ForeignKey(Cohort)
members = models.ManyToManyField(User, related_name='team_members', through='TeamMembers', blank=True)
class TeamMembers(models.Model):
team = models.ForeignKey(Team)
user = models.ForeignKey(User)
Single user can be part of only one team within a cohort.
I want to annotate the new field (boolean) which tells you is the user assigned to some team in the cohort, something like:
User.objects.filter(
members__cohort=cohort
).annotate(
is_team_member=...
)
I am using Python 2.7.13 and Django 1.9.8. Thanks.
I managed to solve the problem by doing the join to the Cohort model and using conditional expressions:
from django.db.models import Case, When, Value, IntegerField
users = User.objects.filter(
members__cohort=cohort
).annotate(
is_team_member=Case(When(team_members__cohort=cohort, then=Value(1)), default=0, output_field=IntegerField())
)
Now I can easily filter, for example, users who are part of some team:
users.filter(is_team_member=1)
I've been looking at the docs for search_fields in django admin in the attempt to allow searching of related fields.
So, here are some of my models.
# models.py
class Team(models.Model):
name = models.CharField(max_length=255)
class AgeGroup(models.Model):
group = models.CharField(max_length=255)
class Runner(models.Model):
"""
Model for the runner holding a course record.
"""
name = models.CharField(max_length=100)
agegroup = models.ForeignKey(AgeGroup)
team = models.ForeignKey(Team, blank=True, null=True)
class Result(models.Model):
"""
Model for the results of records.
"""
runner = models.ForeignKey(Runner)
year = models.IntegerField(_("Year"))
time = models.CharField(_("Time"), max_length=8)
class YearRecord(models.Model):
"""
Model for storing the course records of a year.
"""
result = models.ForeignKey(Result)
year = models.IntegerField()
What I'd like is for the YearRecord admin to be able to search for the team which a runner belongs to. However as soon as I attempt to add the Runner FK relationship to the search fields I get an error on searches; TypeError: Related Field got invalid lookup: icontains
So, here is the admin setup where I'd like to be able to search through the relationships. I'm sure this matches the docs, but am I misunderstanding something here? Can this be resolved & the result__runner be extended to the team field of the Runner model?
# admin.py
class YearRecordAdmin(admin.ModelAdmin):
model = YearRecord
list_display = ('result', 'get_agegroup', 'get_team', 'year')
search_fields = ['result__runner', 'year']
def get_team(self, obj):
return obj.result.runner.team
get_team.short_description = _("Team")
def get_agegroup(self, obj):
return obj.result.runner.agegroup
get_agegroup.short_description = _("Age group")
The documentation reads:
These fields should be some kind of text field, such as CharField or TextField.
so you should use 'result__runner__team__name'.