Imagine there is a model:
class OrgUnit(models.Model):
parent = models.ForeignKey(
'self',
on_delete=models.CASCADE,
verbose_name=_('parent'),
related_name='children',
blank=True,
null=True,
)
name = models.CharField(_('name'), max_length=255)
type = models.CharField(_('type'), max_length=55, null=True, blank=True, db_index=True)
And hierarchy sample:
It is easy find all stores if one knows cluster id (cluster_id=1):
stores = OrgUnit.objects.filter(
type='store',
parent__parent_id=cluster_id
)
It is also easy find cluster by sales department id (sales_department_id=5):
cluster = OrgUnit.objects.select_related('parent__parent').get(pk=sales_department_id).parent.parent
And finally find stores for sales department:
cluster_id = OrgUnit.objects.select_related('parent').get(pk=sales_department_id).parent.parent_id
stores = OrgUnit.objects.filter(type='store', parent__parent_id=cluster_id)
Getting stores by sales department id will make 2 queries to database. I wonder to know whether it possible to fetch stores by sales department id in one query? If yes how?
You can move the hierarchy down again with the children, so querying the ForeignKey relation in reverse:
stores = OrgUnit.objects.filter(
type='store',
parent__parent__children__children__pk=sales_department_id
)
Here we thus query for OrgItems that have a parent that has a parent for which there is a child for which there is a child with as primary key the sales_department_id.
Related
I want to make a flexible online shop which will allow it's admins to create products and add custom product fields without need to program. I did it, but the final database structure is so complicated that I can't figure out how to filter it.
Let's say there are categories with some products attached to it. Each category has only one unique template, the template holds custom fields names and types(int, char). When a product is created, the corresponding template-like fields are written to another model that holds custom fields names and values.
So, how to filter the product model considering its custom fields values? To clarify, let's say someone created smartphones category, created template with fields "Brand" and "Screen size", added some smartphones and wants to filter phones with brand="Apple" and screen size > 4.5 inches.
I hope that makes sense ^_^
Database structure:
class Category(models.Model):
name = models.CharField(max_length=63)
class Product(models.Model):
category = models.ForeignKey(Category, on_delete=models.CASCADE)
name = models.CharField(max_length=63)
price = models.IntegerField(validators=[MinValueValidator(0), MaxValueValidator(1073741823)], null=True, blank=True)
#Template
class CategoryTemplate(models.Model):
category = models.ForeignKey(Category, on_delete=models.CASCADE, null=True)
name = models.CharField(max_length=255, null=True, blank=True)
#Model that holds template custom fields
class TemplateField(models.Model):
template = models.ForeignKey(CategoryTemplate, on_delete=models.CASCADE)
name = models.CharField(max_length=255, null=True, blank=True)
is_integer = models.BooleanField(blank=True, default=False)
#Values of custom char product fields
class ProductPropertiesChar(models.Model):
product = models.ForeignKey(Product, on_delete=models.CASCADE)
property_name = models.CharField(max_length=255, null=True, blank=True)
property_value = models.CharField(max_length=255, null=True, blank=True)
#Values of custom integer product fields
class ProductPropertiesInteger(models.Model):
product = models.ForeignKey(Product, on_delete=models.CASCADE)
property_name = models.CharField(max_length=255, null=True, blank=True)
property_value = models.IntegerField(validators=[MinValueValidator(0), MaxValueValidator(1073741823)], null=True, blank=True)
Maybe this will work. Firstly, I'd strongly recommed using explicit related names!
class ProductPropertiesChar(models.Model):
product = models.ForeignKey(Product, on_delete=models.CASCADE,
related_name='charprop')
...
Simple case: all Products related to a single specified ProductPropertiesChar (the default related name is too horrible to type)
results = Product.objects.filter( charprop__property_name='Brand',
charprop__property_value='Apple' )
You can combine several values with __in or use the other usual __ lookups. You should also be able to .exclude(...).
results = Product.objects.filter( charprop__property_name='Brand',
charprop__property_value__in = ['Apple','Samsung','Google'] )
You ought to be able to use Q objects
q1 = Q( charprop__property_name='Brand',charprop__property_value='Apple' )
q2 = Q( intprop__property_name='ScreenSize', intprop__property_value__gte=130 )
I'm pretty sure or will work
results = Product.objects.filter( q1 | q2 )
I'm not quite so sure about and because you are following the related name to two different objects
results = Product.objects.filter( q1 & q2 ) # not sure
You may instead need to use .intersection (doc here)
qs1 = Product.objects.filter( q1)
qs2 = Productr.objects.filter( q2)
results = qs1.intersection( qs2)
See also .union, .difference
At this poimt I'll admit I'm talking about things I have read about but never tried. You will have to experiment, and read the Django docs over and over again!
I have what i think is a simple question but I am struggling to find out how it works. I get how related name works for foreign keys but with many to many fields it seems to break my brain.
I have two 3 models at play here. A User, TeamMember and Team Model as seen below.
User model is the built in django model.
#TeamMember Model
class TeamMember(models.Model):
member = models.ForeignKey(User, on_delete=models.SET(get_default_team_member), verbose_name='Member Name', related_name="team_members")
...
#Team Model
class Team(models.Model):
name = models.CharField(max_length=50)
manager = models.ForeignKey(TeamMember, on_delete=models.SET_NULL, related_name="managers", null=True, blank=True)
team_lead = models.ForeignKey(TeamMember, on_delete=models.SET_NULL, related_name="tls", null=True, blank=True)
tps = models.ForeignKey(TeamMember, on_delete=models.SET_NULL, related_name="tps", null=True, blank=True)
members = models.ManyToManyField(TeamMember, blank=True, related_name="members")
...
Now in a view i want to access a specific users team. I thought i could do this by doing something like this:
member = TeamMember.objects.get(pk=1)
member_team = member.members.name
However if I print member_name than it prints nothing. If I try to access any of the other fields on that model like member.members.team_lead.first_name it fails to find the team_lead field. I understand that this has a .all() attribute but i thought it was tied to the team object through the members field. So if that member matches the team it would give me the team. So I thought it might be an issue if the same member was linked to more than one team (which is possible) so i tired something like this member.members.all().first().name and i get an error that states it cannot get name from NoneType.
Is there an easy way to get the team name from a relationship like this or am i better off just doing a team query with the user?
Thanks,
jAC
First of all, I would like to point out that you are not using the related_name (and related_query_name parameters in a proper way). I think this SO post will help you to understand the concept in a better way.
So, I would change the related_name (and related_query_name) values in the Team model as below,
class Team(models.Model):
name = models.CharField(max_length=50)
manager = models.ForeignKey(
TeamMember,
on_delete=models.SET_NULL,
related_name="teams",
related_query_name="team",
null=True,
blank=True,
)
team_lead = models.ForeignKey(
TeamMember,
on_delete=models.SET_NULL,
related_name="teams",
related_query_name="team",
null=True,
blank=True,
)
tps = models.ForeignKey(
TeamMember,
on_delete=models.SET_NULL,
related_name="teams",
related_query_name="team",
null=True,
blank=True,
)
members = models.ManyToManyField(
TeamMember, blank=True, related_name="teams", related_query_name="team"
)
...
Now in a view i want to access a specific user's team.
Since the Team and TeamMember models are connected via ManyToManyField, you may have "zero or more" Teams associated with a single TeamMember
So, the following query will get you all the teams associated with a particular TeamMemeber
team_member = TeamMember.objects.get(pk=1)
all_teams = team_member.teams.all()
You can also iterate over the QuerySet as,
team_member = TeamMember.objects.get(pk=1)
for team in team_member.teams.all():
print(team.name)
For anyone wondering what I did based on JPG's advice was the for loop option
team_member = TeamMember.objects.get(pk=1)
teams = [t.name for t in team_member.members.all()]
I personally do not care which team i get as my need in this case is just to pass a team through even if it is none. So i just use team = team[0] if teams.count() > 0 else "No team"
I have two models with ManyToManyField relationship:
class Education(models.Model):
title = models.CharField(default=None, max_length=100)
content = models.TextField(default=None)
price = models.ManyToManyField(Price)
class Price(models.Model):
cost = models.CharField(default=None, max_length=20)
created_at = models.DateTimeField(auto_now=True, null=True, blank=True)
I can fetch all rows like this:
result = Education.objects.filter(price__in=Price.objects.all()).select_related('Price')/
.values_list('title', 'content', 'price__cost', 'price__created_at')
But now i want to group by education.id and the cost parameter should be latest parameter that inserted(based on created_at).
So i want to have list of all Education with latest cost that inserted for every education.
Will it work for you, It will return the respective id
Education.objects.filter(price__in=Price.objects.all()).select_related('Price').values('id').annotate(price_id=Max('price__id'))
I have three models such as the one below and I am trying to write a query that allows me to access all the Day_Type associated to the Day objects that are pointing to a specific JobProject.
I know that I can get all the Day pointing at a JobProject by querying project.jobproject_days.all() and I can get the values of the Day_Type by doing project.jobproject_days.values_list('day_type__name', flat=True)
BUT how can I get the Day_Type themselves?
class JobProject(models.Model):
......
class Day_Type(models.Model):
name = models.CharField(max_length=30)
class Day(models.Model):
....
day_type = models.ForeignKey(Day_Type, blank=True, on_delete=models.CASCADE, null=True, related_name='day_type')
project = models.ForeignKey(JobProject, blank=True, on_delete=models.CASCADE, related_name='jobproject_days', null=True)
You can fetch it like this:
daytypes = Day_Type.objects.filter(day_type__project=project)
I'm fairly new to Django and attempting to store a model which will hold transaction information for a purchase between 2 users; a buyer and seller. I therefore want to store 2 UserIDs:
class Transaction(models.Model):
transactionid = models.AutoField(primary_key=True)
# USERID OF SELLER
# USER ID OF BUYER
orderid = models.ForeignKey('Order', db_column='orderid', on_delete=models.SET_NULL, blank=True, null=True)
status = models.CharField(choices=PAYMENT_STATUS, default='pending', max_length=50)
timestamp = models.DateTimeField(auto_now_add=True)
I want to use the following foreign key:
seller = models.ForeignKey(
settings.AUTH_USER_MODEL,
on_delete=models.CASCADE,
)
however, to my understanding, this will only store the current logged in user which means I wouldn't be able to set both? Is there a better way to do this rather than modifying the model twice (esentially from both accounts)?
Any reccomendations or advice appreciated, thank you!
I hope, in the Transaction model you are going to add the entry if someone made any purchase. Buyer Id you can get from the current user. Seller ID yo can get from the product information.
For adding more than 1 foreign key with the same Model, you can use the related_name parameter.
class Transaction(models.Model):
transactionid = models.AutoField(primary_key=True)
seller = models.ForeignKey(CustomUser, on_delete=models.CASCADE, related_name='seller_name')
buyer = models.ForeignKey(CustomUser, on_delete=models.CASCADE, related_name='buyer_name')