I have something like this:
class Car(models.Model):
model = models.CharField(max_length=200)
brand = models.CharField(max_length=100)
status = models.ManyToMany(Status)
class Status(models.Model):
name = models.CharField(max_length=40)
date = models.DateTimeField('Status creation date')
How can I query all the cars where their last status (most recent) is REPAIRED for instance? Is this achievable in just one query?
from django.db.models import Max
cars = Car.objects.annotate(Max('status__date')).filter(status__name='REPAIRED').distinct()
You may read the Django examples for Many to Many relationships.
Related
I have two models that are related: one is a list of participants. The other is a list of times they have checked in or out of an office.
The table (Checkin) has one record for every checkin/checkout pair. So, there can be many records for any participant.
How can I retrieve only the very last (most recent) record for a participants checkin and then pass the participant and only that most recent Checkin record to my template?
From what I can tell there's no ability to do something like a last() in my template, so how would I go about filtering to get just that single record?
Thank you.
Models:
class Participant(models.Model):
first_name = models.CharField(max_length=50)
middle_initial = models.CharField(max_length=50, blank=True)
class CheckIn(models.Model):
adult = models.ForeignKey(
Participant, on_delete=models.CASCADE, blank=True, null=True, related_name='adult_checkin')
checkin = models.DateTimeField(blank=True, null=True)
checkout = models.DateTimeField(blank=True, null=True)
View snipit:
p_checkins = Participant.objects.all().order_by('created')
queryset = p_checkins
context_object_name = "the_list"
template_name = 'list_of_checkins.html'
You can fetch data through most recent checkin or checkout.
For checkin :
p_checkins = CheckIn.objects.all().order_by('-checkin')[0]
For checkout :
p_checkins = CheckIn.objects.all().order_by('-checkout')[0]
To get the participant name by :
name = p_checkins.adult.first_name
When you use (-) your latest update will be query from database.
p_checkins = CheckIn.objects.all().order_by('-checkin')
or
p_checkins = CheckIn.objects.all().order_by('-checkout')
you can annotate the latest value via a subquery to the participant
from django.db.models import OuterRef, Subquery
checkin_q = CheckIn.objects.filter(adult=OuterRef('pk')).order_by('-checkin')
queryset = Participant.objects.annotate(last_checkin=Subquery(checkin_q.values('checkin')[:1]))
see https://docs.djangoproject.com/en/4.0/ref/models/expressions/#subquery-expressions
Most of the answers so far are correct in several aspects. One thing to note is that if your check_in or check_out values (whichever you use) isn't chronological (and by "most recent", you mean the last added), you'll want to add a created_at datetime field with auto_now option True, or order by the pk.
In addition to the other answers provided and my comment above, you can also get the most recent check in by using the related manager on the participant object.
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.
i am using django(3.1.5). and i am trying to get parent model to child model by filter query
i have model like -
class Product(models.Model):
product_name = models.CharField(max_length=255, unique=True)
is_feature = models.BooleanField(default=False)
is_approved = models.BooleanField(default=False)
created_at = models.DateTimeField(auto_now_add=True)
class ProductGalleryImage(models.Model):
product = models.ForeignKey(Product, on_delete=models.CASCADE)
product_gallery_image = models.FileField(upload_to='path')
is_feature = models.BooleanField(default=False)
i am getting data from SELECT * FROM products_product AS pp INNER JOIN products_productgalleryimage AS ppgi ON ppgi.product_id = pp.id WHERE ppgi.is_feature=1 AND pp.is_feature=1 AND is_approved=1 ORDER BY pp.created_at LIMIT 4 mysql query.
so how can i get data like this query in django filter query
Firstly you can add related_name to ProductGalleryImage for better query support like this
product = models.ForeignKey(Product, on_delete=models.CASCADE, related_name='product_images')
Then your query should be like this
products=Product.objects.filter(is_approved=True, is_feature=True, product_images__is_feature=True).order_by('created_at')[:4]
You can simply loop over the other related model like so:
for product_gallery_image in product_instance.productgalleryimage_set.all():
print(product_gallery_image.product_gallery_image)
The productgalleryimage_set here is simply the related model name in lowercase with _set appended. You can change this by setting the related_name attribute on the foreign key.
Note: This will perform a query to fetch each of the product_gallery_image objects of some product instance.
If you want to get the first object only:
product_gallery_image = product_instance.productgalleryimage_set.first()
If you want to perform a join as in your example which will perform only one query you can use select_related (this will only work in forward direction for reverse direction look at prefetch_related):
product_gallery_images = ProductGalleryImage.objects.all().select_related('product')
for product_gallery_image in product_gallery_images:
print(product_gallery_image.product.product_name)
print(product_gallery_image.product_gallery_image)
I am struggling to understand django models relationship.
I have this arborescence:
A train have cars, and those cars are divided into parts. Then those parts all contains different references.
Like, for exemple, all the trains have the 6 cars, and the cars 6 parts. Each part have x reference to be associated.
I would like to use all of them in a template later on, where the user can select the train, the car and the part he worked on, then generate a table from his selections with only the references associated to the parts he selected.
It should update the train and the car (I'm trying to update a stock of elements for a company)
I dont really understand which model field give to each of them. After checking the doc, Ive done something like this but i am not convinced:
class Train(Car):
train = models.CharField(max_length=200)
id = models.CharField(primary_key='True', max_length=100)
selected = models.BooleanField()
class Meta:
abstract = True
class Car(Part):
car = models.CharField(max_length=200)
id = models.CharField(primary_key='True', max_length=100)
selected = models.BooleanField()
class Meta:
abstract = True
class Part(Reference):
part = models.CharField(max_length=200)
id = models.CharField(primary_key='True', max_length=100)
selected = models.BooleanField()
class Meta:
abstract = True
class Reference(models.Model):
reference = models.CharField(max_length=200)
id = models.CharField(primary_key='True', max_length=100)
selected = models.BooleanField()
def __str__(self):
return self.reference
Can someone please help me understand this so I can do well ? Thanks!!
1-)if you add abstract = True in your Model Meta class, your class doesn't created on database as a table. If you store data for any class, you mustn't define abstract = True.
2-)For relations, you can use models.ForeignKey . If you add a class into brackets of another class, it names: inheritance.(You can think like parent-child relation). In database management, we can use foreignkey for one-to-many relationship.
3-)In Django ORM, id field automatically generated. So you don't need to define id field.
If I understand correctly, also you want to store parts of user's selected.
So, your model can be like that:
class Train(models.Model):
name = models.CharField(max_length=200) # I think you want to save name of train
class Car(models.Model):
train = models.ForeignKey(Train,on_delete=models.Cascade)
name = models.CharField(max_length=200)
class Part(models.Model):
car = models.ForeignKey(Car,on_delete=models.Cascade)
name = models.CharField(max_length=200)
class Reference(models.Model):
part = models.ForeignKey(Part,on_delete=models.Cascade)
name = models.CharField(max_length=200)
def __str__(self):
return self.reference
#addtional table for storing user's references
class UserReference(models.Model):
user = models.ForeignKey(User,on_delete=models.Cascade)
reference = models.ForeignKey(Reference,on_delete=models.Cascade)
name = models.CharField(max_length=200)
With this definitions, you can store user's definition on UserReference table. And with Django Orm, you can access train object from UserReferenceObject.
#user_reference: UserReference object like that result of UserReference.objects.first()
user_reference.reference.part.car.train.name
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'.