How can i join two prefetch related in Django query - django

i have to do a django filter with complex form query and i don't have experience with select_related and prefetch_related methods.
models.py:
class User(models.Model):
class Park(models.Model):
class Plot(models.Model):
owner = models.ForeignKey(get_user_model(), verbose_name=_('Owner'), on_delete=models.SET_NULL, null=True, related_name='plots')
park = models.ForeignKey('Park', verbose_name=_('Park'), on_delete=models.SET_NULL, null=True, related_name='plots')
class Building(models.Model):
plot = models.ForeignKey('Plot', verbose_name=_('Plot'), on_delete=models.SET_NULL, blank=True, null=True, related_name='plot_buildings')
owner = models.ForeignKey(get_user_model(), verbose_name=_('Owner'), on_delete=models.SET_NULL, blank=True, null=True, related_name='owner_buildings')
tenant = models.ForeignKey(get_user_model(), verbose_name=_('Tenant'), on_delete=models.SET_NULL, blank=True, null=True, related_name='tenant_buildings')
I need to get all de user that are owner of a plot or a building or tenant of a building.
i have this for now...
filters.py:
class UserApiFilter(filters.FilterSet):
park_id = filters.CharFilter(method='filter_by_park')
def filter_by_park(self, queryset, name, value):
params = {name: value}
result = queryset.prefetch_related(Prefetch('plots', queryset=app_models.Plot.objects.filter(**params)))
Anybody could help me please?
Thanks in advance.

For now i have this solution:
params = {'park__id': value}
plots = app_models.Plot.objects.filter(**params)
users_plots = list(map(lambda x: x.owner, plots))
params = {'plot__park__id': value}
buildings = app_models.Building.objects.filter(**params)
users_buildings_owners = list(map(lambda x: x.owner, buildings))
users_buildings_tenats = list(map(lambda x: x.tenant, buildings))
result = list(map(lambda x: x.id, set(users_plots + users_buildings_owners + users_buildings_tenats)))
return queryset.filter(id__in=result)

Related

When I open the model, one field value is replaced automatically

Have a stupid issue: When I open the employee model (in django admin), one field (employee_type) value is replaced automatically, idk why...
Example: I create employee, define employee type as manager, save. In DB value is manager. After that, I open employee and see employee type as sewer and if I save, that value will saved in DB.
I created text choices for this field, and In DB field is defined as enum.
I tried to research the issue, value isn't used from DB, always first value from text choices is used.
By the way, I created same fields (enum in DB and text choices in the model) in other model. And all works properly.
How can I fix it???
Models.py with the issue:
class Employee(models.Model):
class EmployeeType(models.TextChoices):
SEWER = 'SEWER', _('Sewer')
MANAGER = 'MANAGER', _('Manager')
UNDEFINED = 'UNDEFINED', _('Undefined')
user = models.OneToOneField(User,
models.CASCADE,
db_column='user',
verbose_name=_('User'),
primary_key=True)
employee_type = models.CharField(db_column='Employee type',
verbose_name=_('Employee type'),
max_length=9,
choices=EmployeeType.choices,
default=EmployeeType.UNDEFINED)
phone = models.CharField(db_column='Phone',
verbose_name=_('Phone'),
max_length=255)
work_xp = models.IntegerField(db_column='Work XP',
verbose_name=_('Work XP'),
blank=True,
null=True)
Another one models.py. With same fields but without issues:
class Order(models.Model):
class OrderStatus(models.TextChoices):
CREATED = 'Created', _('Created')
CANCELLED = 'Cancelled', _('Cancelled')
IN_PROGRESS = 'In progress', _('In progress')
COMPLETED = 'Completed', _('Completed')
PASSED_TO_CLIENT = 'Passed to the client', _('Passed to the client')
RETURNED_FOR_REWORK = 'Returned for rework', _('Returned for rework')
class Urgency(models.TextChoices):
LOW = 'Low', _('Low urgency')
MEDIUM = 'Medium', _('Medium urgency')
HIGH = 'High', _('High urgency')
VERY_HIGH = 'Very high', _('Very high urgency')
class LabourIntensity(models.TextChoices):
LOW = 'Low', _('1-3 days')
MEDIUM = 'Medium', _('4-6 days')
HIGH = 'High', _('7-9 days')
VERY_HIGH = 'Very high', _('10+ days')
class PaymentStatus(models.TextChoices):
PENDING = 'Pending payment', _('Pending payment')
PREPAYMENT_MADE = 'Prepayment made', _('Prepayment made')
PAID = 'Paid', _('Paid')
id_service = models.ForeignKey(Service,
models.SET_NULL,
db_column='id_Service',
verbose_name=_('Service'),
blank=True,
null=True)
status = models.CharField(db_column='Status',
verbose_name=_('Status'),
max_length=20,
choices=OrderStatus.choices,
default=OrderStatus.CREATED)
payment_status = models.CharField(db_column='Payment status',
verbose_name=_('Payment status'),
max_length=15,
choices=PaymentStatus.choices,
blank=True,
null=True)
prepayment = models.DecimalField(db_column='Prepayment',
verbose_name=_('Prepayment'),
max_digits=19,
decimal_places=2,
blank=True,
null=True)
cost = models.DecimalField(db_column='Cost',
verbose_name=_('Cost'),
max_digits=19,
decimal_places=2,
blank=True,
null=True)
start_date = models.DateTimeField(db_column='Start date',
verbose_name=_('Start date'),
blank=True,
null=True)
end_date = models.DateTimeField(db_column='End date',
verbose_name=_('End date'),
blank=True,
null=True)
id_client = models.ForeignKey(Client,
models.SET_NULL,
db_column='id_Client',
verbose_name=_('Client'),
blank=True,
null=True)
id_employee = models.ForeignKey(Employee,
models.SET_NULL,
db_column='id_Employee',
verbose_name=_('Employee'),
blank=True,
null=True)
labour_intensity = models.CharField(db_column='Labour intensity',
verbose_name=_('Labour intensity'),
max_length=9,
choices=LabourIntensity.choices,
default=LabourIntensity.LOW)
urgency = models.CharField(db_column='Urgency',
verbose_name=_('Urgency'),
max_length=9,
choices=Urgency.choices,
default=Urgency.LOW)
materials = models.ManyToManyField(Material, through='OrderMaterials')
comment = models.TextField(db_column='Comment',
verbose_name=_('Comment'),
blank=True,
null=True)
I solved this issue.
In DB a type of field "employee_type" was defined as:
ENUM('Undefined','Sewer','Manager')
But the model has EmployeeType choices with uppercase.
Solution: I changed lowercase to uppercase of the values in the field type in DB:
ENUM('UNDEFINED','SEWER','MANAGER')
Now everything works fine.

Django Joining Tables

I am trying to get the information from one table filtered by information from another table (I believe this is called joining tables).
I have these two models:
class Listing(models.Model):
title = models.CharField(max_length=64)
description = models.CharField(max_length=500)
price = models.DecimalField(max_digits=11, decimal_places=2, validators=[MinValueValidator(Decimal('0.01'))])
category = models.ForeignKey(Category, on_delete=models.CASCADE, default="")
imageURL = models.URLField(blank=True, max_length=500)
creator = models.ForeignKey(User, on_delete=models.CASCADE, related_name="creator", default="")
isOpen = models.BooleanField(default=True)
def __str__(self):
return f"{self.id} | {self.creator} | {self.title} | {self.price}"
class Watchlist(models.Model):
listing = models.ForeignKey(Listing, on_delete=models.CASCADE, related_name="listingWatched", default="")
user = models.ForeignKey(User, on_delete=models.CASCADE, related_name="userWatching", default="")
What I need to do is to get all the listings from a specific user Watchlist, the idea is to generate a page with all of the information of each of the listings that are in the user's watchlist. What should I do?
Thanks in advance!
Since is a foreign key, in Django you can access the information by calling the attribute
For example:
my_user = Watchlist.objects.get(pk=1)
print(my_user.listing.title)
You can also access to that attrbute in a query in case you need to filter upwards some value
values = Watchlist.objects.all().filter(listing__title='MyTitle')
my_titles = [x.title for x in values]
print(my_titles)
Or in your case, if you want to list all the title for a specific user
values = Watchlist.objects.all().filter(user='foo_user')
my_titles = [x.listing.title for x in values]
print(my_titles)
More documentation here

Retrieve items from Many-to-Many relationship in Django query

Models.py
class SalesOrderItems(models.Model):
item = models.ForeignKey(MasterItems, on_delete=models.CASCADE)
item_quantity = models.IntegerField(default=0)
class SalesOrder(models.Model):
delivery_method_choice = (('Full-Truck Load', 'Full-Truck Load'), ('Part-Truck Load', 'Part-Truck Load'))
status_choices = (('On Hold', 'On Hold'),('Ready to Dispatch', 'Ready to Dispatch'),('Dispatched', 'Dispatched'))
owner = models.ForeignKey(Teacher, on_delete=models.CASCADE, related_name='so_owner')
client = models.ForeignKey(MasterClient, on_delete=models.CASCADE, related_name='so_client')
reference_no = models.CharField(max_length=500, blank=True, null=True)
date = models.DateField(default=datetime.date.today)
shipment_date = models.DateField(default=datetime.date.today)
delivery_method = models.CharField(max_length=500, default='Full-Truck Load', choices=delivery_method_choice)
items = models.ManyToManyField(SalesOrderItems, related_name='items_so', blank=True, null=True)
status = models.CharField(max_length=500, default='On Hold', choices=status_choices)
origin = models.CharField(max_length=255)
destination = models.CharField(max_length=255)
I want to retrieve the items of a particular sales order by django query
My attempt to get the items:
items = []
for i in sales_orders:
so = SalesOrder.objects.filter(pk=i)[0]
print("items",so.items)
Output:
items classroom.SalesOrderItems.None
How can I get the list of items in a particular SalesOrder ??
sales_orders = SalesOrder.objects.prefetch_related('items').filter(**sales_filter_here)
for sales_order in sales_orders:
for sales_order_item in sales_order.items.all():
print(sales_order_item)
this query will work for you
SalesOrder.objects.filter(id=1).values_list('items__item__item_name')
below is my simple Masteritems model
class MasterItems(models.Model):
item_name = models.CharField(max_length=50)
def __str__(self):
return self.item_name
by this way you will get every item name in queryset. this is my simple output
<QuerySet [('rice',), ('pepsi',), ('Computer',)]>

Django : Create custom object list in the view and pass it to template to loop over

I want to create a custom object list in the view and pass it to the template. In the template I want to loop over the list and display the information.
My models are
class CustomUser(AbstractUser):
def __str__(self):
return self.email
class Post(models.Model):
author = models.ForeignKey(CustomUser,on_delete=models.CASCADE,)
text = models.TextField()
created_date = models.DateTimeField(default=timezone.now)
published_date = models.DateTimeField(blank=True, null=True)
post_url = models.URLField(max_length = 200, blank = True)
slug = models.SlugField(unique=True, blank=True)
class subscription(models.Model):
creator = models.ForeignKey(CustomUser,default=None, null=True,on_delete=models.CASCADE,related_name='creator',)
booster = models.ForeignKey(CustomUser,default=None, null=True,on_delete=models.CASCADE,related_name='booster')
sub_value = models.FloatField(blank = True)
sub_id = models.TextField(blank = True)
status = models.BooleanField(default=False)
dateSubscribed = models.DateTimeField(default=timezone.now)
dateSubscriptionEnded = models.DateTimeField(default=timezone.now)
paymentCount = models.FloatField(default= 0)
I want to filter objects from subscription model like below
subs = subscription.objects.filter(booster = request.user)
Then find creators in the above subs object list and for each creator get the name, numbers Posts, and number of Subscribers. Add this to custom list and pass it to the template to loop over and display the information in the template. Can someone help me how to create this custom list. Thanks!
Ok so here are the basics minus the subscribers because I don't see the relation clearly. This is how to parse the name and the number of posts. \
my_list = []
for sub in subs:
name = sub.creator.name
auth_id = sub.creator.id
posts = Post.objects.filter(author=auth_id)
num_of_posts = len(posts)
my_list.append({
'name':name,
'post_count': num_of_posts,
})
then you would pass mylist thru the template context.
It is a common mistake to name the related_name=… parameter [Django-doc] to the same value as the name of the field. The related_name parameter however is the name of the reverse relation Django will automatically add. So here it means a relation to access for example the related subscription objects of a given CustomUser.
Therefore it makes more sense to rename these, for example like:
class Subscription(models.Model):
creator = models.ForeignKey(
CustomUser,
default=None,
null=True,
on_delete=models.CASCADE,
related_name='created_subscriptions'
)
booster = models.ForeignKey(
CustomUser,
default=None,
null=True,
on_delete=models.CASCADE,
related_name='boosted_subscriptions'
)
sub_value = models.FloatField(blank=True)
sub_id = models.TextField(blank =True)
status = models.BooleanField(default=False)
dateSubscribed = models.DateTimeField(default=timezone.now)
dateSubscriptionEnded = models.DateTimeField(default=timezone.now)
paymentCount = models.FloatField(default=0)
Next we can make a query where:
from django.db.models import Count
CustomUser.objects.filter(
created_subscriptions__booster=request.user
).annotate(
number_of_posts=Count('post', distinct=True)
)
This is a QuerySet of CustomUsers where each CustomUser that arises from this QuerySet has an extra attribute .number_of_posts that contains the number of posts. You thus can iterate over the queryset directly in the template.

Django: Are multiple Generic Relations in one Model bad design?

I have a model with multiple Generic Relations that has become very complicated to use in my templates. The model is a 'Gig' or musical event that takes place at a 'Venue' and/or a 'Festival' and has a 'Musician' and/or an 'Ensemble'.
Where it gets complicated is that each 'Gig' has a presenter, promoter and an agent. These are setup as generic relations to other models such as 'PresenterCompany'. A Presenter company could be a promoter, presenter, or agent, or all of them for the same gig. Here are the models (simplified for ref):
class Gig(models.Model):
description = models.CharField(max_length=100, blank=True)
date = models.DateTimeField()
venue = models.ForeignKey(Venue)
festival = models.ForeignKey(Festival, blank = True, null=True)
musician = models.ManyToManyField(Musician, blank=True)
ensembles = models.ManyToManyField(Ensemble, blank = True)
presenter_content_type = models.ForeignKey(ContentType,
limit_choices_to={"model__in": ("Individual", "ArtsOrganization",'Presenter', "BookingAgent","Festival", "OtherOrganization","PresenterCompany", "Venue")}, related_name = "Presenter Type", verbose_name = "Presenter",blank=True, null=True)
presenter_id = models.IntegerField(db_index=True, blank=True, null=True, verbose_name='Presenter ID')
presenter = generic.GenericForeignKey('presenter_content_type','presenter_id')
promoter_content_type = models.ForeignKey(ContentType,
limit_choices_to={"model__in": ("Individual", "ArtsOrganization","BookingAgent","Presenter", "Festival", "OtherOrganization","PresenterCompany", "Venue")}, related_name = "promotor", verbose_name='Promoter Type', blank=True, null=True)
promoter_id = models.IntegerField(db_index=True, blank=True, null=True, verbose_name='Promoter ID')
promoter = generic.GenericForeignKey('promoter_content_type','promoter_id')
agent_content_type = models.ForeignKey(ContentType,
limit_choices_to={"model__in": ("Individual", "BookingAgent")}, related_name="agent", verbose_name='Agent Type', blank=True, null=True)
agent_id = models.IntegerField(db_index=True, blank=True, null=True, verbose_name='Agent ID')
agent = generic.GenericForeignKey('agent_content_type','agent_id')
class PresenterCompany(models.Model):
name = models.CharField(max_length=70)
address =GenericRelation(Address)
presented_gig = GenericRelation('Gig',
content_type_field='presenter_content_type',
object_id_field='presenter_id',
related_name='presenter_presented_gig'
)
promoted_gig = GenericRelation('Gig',
content_type_field='promoter_content_type',
object_id_field='promoter_id',
related_name='presenter_promoted_gig'
)
booked_gig = GenericRelation('Gig',
content_type_field='promoter_content_type',
object_id_field='promoter_id',
related_name='presenter_booked_gig'
)
The main issue is that when I try to get all of the gigs for a presenter company, I have to write three different for loops for each role i.e. {% for gig in presentercompany.presented_gig.all %}, and so on... This seems like redundant code.
Is there a better way to structure this such as using intermediary models for presenter, promoter, and agent? Thanks for your advice!
Generic relationships can definitely be hard to deal with. I would only use them when there is no other option.
In your case, I see a couple other options. You could have a ManyToMany relationship between PresenterCompany and Gig using a through table to specify the type of relationship (https://docs.djangoproject.com/en/2.0/topics/db/models/#extra-fields-on-many-to-many-relationships):
class Gig(models.Model):
description = models.CharField(max_length=100, blank=True)
date = models.DateTimeField()
venue = models.ForeignKey(Venue)
festival = models.ForeignKey(Festival, blank=True, null=True)
musician = models.ManyToManyField(Musician, blank=True)
ensembles = models.ManyToManyField(Ensemble, blank=True)
class PresenterCompanyGigRelationship(models.Model):
gig = models.ForeignKey(Gig, on_delete=models.CASCADE)
presenter_company = models.ForeignKey(
'PresenterCompany', on_delete=models.CASCADE)
relationship = models.CharField(
max_length=10,
choices=(
('presenter', 'Presenter'),
('promoter', 'Promoter'),
('agent', 'Agent'),
))
class PresenterCompany(models.Model):
name = models.CharField(max_length=70)
git = models.ManyToManyField(Gig, through=PresenterCompanyGigRelationship)