Using Django 1.8
I have an unmanaged model that points to a view in the db and I'm trying to return a queryset based on a derived field.
Here is a basic example of the model structure:
class Book(models.Model):
book_id = models.IntegerField()
publisher = models.CharField(max_length=20, null=True) # Can join to Publisher.publisher_name
sku = models.CharField(max_length=15, null=True) # Can join to Sku.sku
class Meta:
managed = False
db_table = 'vw_book'
class Sku(models.Model):
sku = models.CharField(max_length=15)
publisher = models.ForeignKey('myapp.Publisher')
class Publisher(models.Model):
publisher_name = models.CharField(max_lenth=20)
region = models.ForeignKey('myapp.Region')
class Region(models.Model):
region_name = models.CharField(max_length=20)
I'm looking for a way to return a queryset of Book based on the region, derived from the publisher as the preferred field and then the sku. It is possible for these fields in Book to refer to different region fields as the data is unlcean and has been derived from multiple sources. I can add a method to the Book model to derive the region, but trying to get a queryset from this is too slow.
class Book(models.Model):
publisher = models.CharField(max_length=20, null=True)
sku = models.CharField(max_length=15, null=True)
class Meta:
managed = False
db_table = 'vw_book'
def get_region(self):
if not self.publisher:
if not self.sku:
return ''
try:
sku = Sku.objects.get(sku=self.sku)
return sku.publisher.region.region_name
except Sku.DoesNotExist:
return ''
try:
publisher = Publisher.objects.get(publisher_name=self.publisher)
return publisher.region.region_name
except Publisher.DoesNotExist:
return ''
region_dict = {}
for book in Book.objects.all():
region_dict.setdefault(book.get_region(), []).append(book.book_id)
Book.objects.filter(book_id__in=region_dict.get('UK', []))
I am unable to add an extra field to the Book model. Is there a more efficient way I can do this?
I would filter the skus and then filter books based on the skus you receive
skus = Sku.objects.filter(publisher__region__region_name=region).values_list('sku', flat=True)
Book.objects.filter(sku__in=skus)
You can do the same with publishers if need be and do an Or query.
.filter(Q(publisher__in=publishers) |Q(sku__in=skus))
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In Warehouse(models.Model) I have amount attribute and
in ChosenProduct(models.Model) - quantity
I'm trying to get amount in Warehouse through chosen_products instance in App_formSerializer to add the quantity of chosen_product
But I can not get the chosen_products objects from instance
--> below Out:
class WarehouseSerializer(serializers.ModelSerializer):
category_name = serializers.ReadOnlyField(
source='category_product.category_name')
posted_user = serializers.ReadOnlyField(
source='posted_user.username')
class Meta:
model = Warehouse
fields = ['id', 'category_product', 'category_name', 'condition',
'product_name', 'amount', 'barcode', 'f_price', 'created_at', 'updated_at', 'posted_user']
class ChosenProductSerializer(serializers.ModelSerializer):
product_info = WarehouseSerializer(source='product', read_only=True)
period_info = Product_periodSerializer(source='period', read_only=True)
class Meta:
model = ChosenProduct
exclude = ('app_form',)
class App_formSerializer(serializers.ModelSerializer):
chosen_products = ChosenProductSerializer(many=True)
def update(self, instance, validated_data):
instance.terminated = validated_data.get('terminated', instance.terminated)
if instance.terminated == True :
print('-----------TRUE--------------------')
print(instance.chosen_products)
print('-----------PRINT--------------------')
instance.save()
return instance
class Meta:
model = App_form
fields = '__all__'
Out
-----------TRUE--------------------
creditapi.ChosenProduct.None
-----------PRINT--------------------
QUESTION UPDATED
models.py
class Warehouse(models.Model):
category_product = models.ForeignKey(
Category_product, on_delete=models.CASCADE)
product_name = models.CharField(max_length=200, unique=True)
condition = models.BooleanField(default=False)
amount = models.IntegerField()
barcode = models.BigIntegerField()
f_price = models.CharField(max_length=255, null=True)
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
posted_user = models.ForeignKey(User, on_delete=models.CASCADE, default=1)
def __str__(self):
return self.product_name
class App_form(models.Model):
phone_regex = RegexValidator(regex=r'^\+?1?\d{9,12}$', message="Phone number must be entered in the format: '998981234567'. Up to 12 digits allowed.")
terminated = models.BooleanField(default=False)
name = models.CharField(max_length=150)
phone_number = models.CharField(validators=[phone_regex], max_length=13)
def __str__(self):
return self.surname
class ChosenProduct(models.Model):
product = models.ForeignKey(Warehouse, on_delete=models.CASCADE)
quantity = models.IntegerField()
app_form = models.ForeignKey(App_form, on_delete=models.CASCADE, related_name='chosen_products')
def __str__(self):
return self.product.product_name
If you write instance.chose_products you access the manager, not the QuerySet that contains the items. You can use .all() to obtain the QuerySet with all the objects:
print(instance.chosen_products.all())
If you access a ForeignKey in reverse, you have a manager, since zero, one, or more elements can refer to the instance.
You can for example aggregate over the chose_products, for example if you want to retrieve the number of related chose_products, you can use:
print(instance.chosen_products.count())
I would however advise not store (aggregated) data in the App_form, but aggregate data when you need it. Data duplication is an anti-pattern, and it turns out it is hard to keep data in sync.
I have two models in my Django-REST application.
a ProjectRequest and a ContactRequest
I want to make it so, each Projectrequest contains a list of the refered Contactrequests.
class ProjectRequest(models.Model):
project_name = models.CharField(max_length=50)
company_name = models.CharField(max_length=50)
#make array of technologiestechnologies = models.ArrayField(base_field=) (blank=True)
project_description = models.CharField(max_length=200)
project_type = models.CharField(max_length=30)
budget_estimation = models.IntegerField(
default=1000,
validators=[
MinValueValidator(1800),
MaxValueValidator(5000000)
])
#time_estimation = models.DateTimeField(default=None, blank=True, null=True)
class ContactRequest(models.Model):
topic = models.CharField(max_length=30)
description = models.CharField(max_length=200)
time = models.CharField(max_length=15)
project_request = models.ForeignKey(ProjectRequest,
on_delete=models.CASCADE)
so far I have established a relationship, with a foreign key, which works fine as of now. However I want to extends the functionality, so, that the ProjectRequest contains a list of all the projectrequest. I have tried with several different fields, without any luck, and the documentation I can only find fields for ManyToMany and OneToOne. How can this be achieved?
There are many ways to achive what you want. For that, lets add a reverse relation in model named contact_requests:
project_request = models.ForeignKey(ProjectRequest, on_delete=models.CASCADE, related_name="contact_requests")
Now you can use PrimaryKeyRelatedField to show Primary Keys of the ContactRequest attached to each ProjectRequest.
class ProjectRequestSerializer(serializers.ModelSerializer):
contact_requests = serializers.PrimaryKeyRelatedField(many=True, read_only=True)
class Meta:
model = ProjectRequest
fields = ('contact_requests', 'company_name', ...) # other fields
Or if you want all the values of each contact_requests, then you can use nested relationship like this:
class ProjectRequestSerializer(serializers.ModelSerializer):
contact_requests = ContactRequestSerializer(many=True, read_only=True)
class Meta:
model = ProjectRequest
fields = ('contact_requests', 'company_name', ...) # and so on
You could add a property function to the ProjectRequest class that retruns all the ContactRequests that are related to that ProjectRequest like so...
class ProjectRequest(models.Model):
project_name = models.CharField(max_length=50)
company_name = models.CharField(max_length=50)
#make array of technologiestechnologies = models.ArrayField(base_field=) (blank=True)
project_description = models.CharField(max_length=200)
project_type = models.CharField(max_length=30)
budget_estimation = models.IntegerField(
default=1000,
validators=[
MinValueValidator(1800),
MaxValueValidator(5000000)
])
#time_estimation = models.DateTimeField(default=None, blank=True, null=True)
#property
def contact_requests(self):
return ContactRequest.objects.filter(project_request=self)
class ContactRequest(models.Model):
topic = models.CharField(max_length=30)
description = models.CharField(max_length=200)
time = models.CharField(max_length=15)
project_request = models.ForeignKey(ProjectRequest,
on_delete=models.CASCADE)
I had this problem too. This is how I solved it:
ContactRequest= models.ManyToManyField(ContactRequest,related_name="+")
I am trying to do what one might consider an advanced sql query and would like to know if its possible in Django without resorting to raw sql (I will if its necessary).
I want to join 1 or another table based on a value located in a table lookup table and would like to do this entirely in python/django.
The following are rough examples of the models I am using:
class SpecificProduct(models.Model):
specific_product_id = models.AutoField(primary_key=True)
a_field = models.TextField()
something_specific_to_this_model = models.CharField()
class GeneralProduct(models.Model):
other_product_id = models.AutoField(primary_key=True)
text = models.TextField()
TABLE_CATEGORIES = {
1 : SpecificProduct,
2 : GeneralProduct,
}
class ProductCategory(models.Model):
category_id = models.AutoField(primary_key=True)
table_category = models.IntegerField() # Technically represents a table.
category_text = models.CharField(max_length=20)
class Inventory(models.Model):
inventory_id = models.AutoField(primary_key=True)
product_category = models.ForeignKey(ProductCategory, on_delete=models.CASCADE)
product_pk = models.IntegerField() # Technically foreign key to a product table.
quantity = models.IntegerField()
What I want is a method like:
def get_product(category_id, product_pk):
# SQL query magic
return one_object_of_a_specific_product_type
This method should be able to do things like...
Give me the product (model) where the product_category = 1 and the
product_pk = 1. (returns a SpecificProduct model)
Give me the product where product_category = 2 and the product_pk = 50
(returns a GeneralProduct model)
How do you do this query in Django and is this even possible?
Edit:
Based on Kireeti K's response I have created models that look like the following:
from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes.fields import GenericForeignKey
class SpecificProduct(models.Model):
specific_product_id = models.AutoField(primary_key=True)
specific_text = models.TextField()
class GeneralProduct(models.Model):
general_product_id = models.AutoField(primary_key=True)
text = models.TextField()
class ProductCategoryLookup(models.Model):
category_id = models.ForeignKey(ContentType, on_delete=models.CASCADE, primary_key=True)
category_text = models.CharField(max_length=20)
class Inventory(models.Model):
inventory_id = models.AutoField(primary_key=True)
product_category = models.ForeignKey(ContentType, on_delete=models.CASCADE)
product_id = models.PositiveIntegerField()
product = GenericForeignKey('product_category', 'product_id')
quantity = models.IntegerField()
def get_product(category_id, product_pk):
content_type = ContentType.objects.get(id=category_id)
inventory = Inventory.objects.get(product_category=content_type, product_id=product_pk).first()
return inventory.product
You can use a generic-foreign-key to get foreign-key relation with any model sort of dynamically, read about it here. https://docs.djangoproject.com/en/2.1/ref/contrib/contenttypes/#generic-relations
If you rewrite your models using generic-foreign-key then it looks something like this.
class ProductCategory(models.Model):
category_id = models.AutoField(primary_key=True)
content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
object_id = models.PositiveIntegerField()
table_category = models. GenericForeignKey() # Technically represents a table.
category_text = models.CharField(max_length=20)
class Inventory(models.Model):
inventory_id = models.AutoField(primary_key=True)
product_category = models.ForeignKey(ProductCategory,
on_delete=models.CASCADE)
content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
object_id = models.PositiveIntegerField()
product = models. GenericForeignKey() # Technically foreign key to a product table.
quantity = models.IntegerField()
Now to achieve what you want, you can implement your function like this.
def get_product(model=None, category_id, product_pk):
model = "specificproduct" if model else "generalproduct"
content_type = ContentType.objects.get(model=model)
inventory = Inventory.objects.get(product_category_id=category_id, object_id=product_pk, content_type=content_type)
return inventory.product
How to join 3 or more tables in django (ORM ) and fetch the results?
Have created 3 models:
1.student
2.marks
3.details
class Student:
s_id = models.IntegerField(primary_key=True)
s_name = models.CharField(max_length=100)
class Marks:
school_id = models.IntegerField(primary_key=True)
s_id = models.ForeignKey(Student, on_delete=models.CASCADE)
score = models.IntegerField()
status = models.CharField(max_length=30)
class Details:
address_city = models.CharField(max_length=30)
emailid = models.EmailField()
school_id = models.ForeignKey(Marks,on_delete=models.CASCADE)
accomplishments = models.TextField()
I need to join these 3 tables and fetch student name,score,status,address_city,email_id,accomplishments.
In SQL we can write like this:
select s_name, score, status, address_city, email_id,
accomplishments from student s inner join marks m on
s.s_id = m.s_id inner join details d on
d.school_id = m.school_id;
Please let me know how to achieve same thing using DJANGO codes.
Some Suggestions for given models:
models.py:
class Student:
name = models.CharField(max_length=100)
class Marks:
student = models.ForeignKey(Student, on_delete=models.CASCADE)
score = models.IntegerField()
status = models.CharField(max_length=30)
class Details:
address_city = models.CharField(max_length=30)
emailid = models.EmailField()
school = models.ForeignKey(Marks,on_delete=models.CASCADE)
accomplishments = models.TextField()
Now, Create your mapping model as we create mapping table in sql:
class StundetMarksDetailsMap:
student = models.ForeignKey(Student, on_delete=models.CASCADE)
marks = models.ForeignKey(Marks, on_delete=models.CASCADE)
details = models.ForeignKey(Details, on_delete=models.CASCADE)
Now you can create your own queryset as you want in views.py or where you want:
class StudentView(generic.DetailsView):
model = Student
template = student_details.html
//this will return all values related student
def get_queryset(self):
return StundetMarksDetailsMap.objects.filter(student=Student)
Basically this get_queryset returns objects of models which are related to stundet which was picked, use returned objects of Details and Marks to call their corresponding fields in your template. Also use only those fields which you want to display.
Hope this works for you too. All the best :)
I think you should keep it simple rather than complicating models which won't be great when you have a lot of data. Keep the student model as the main Class. And store all other info in other tables.
class Student:
name = models.CharField(max_length=100)
marks = models.ForeignKey(Marks,on_delete=models.CASCADE)
school = models.ForeignKey(School,on_delete=models.CASCADE)
class Marks:
score = models.IntegerField()
status = models.CharField(max_length=30)
class Details:
address_city = models.CharField(max_length=30)
emailid = models.EmailField()
accomplishments = models.TextField()
class School:
name = models.CharField(max_length=30)
details = models.ForeignKey(Details)
Now do the below query
student = Student.objects.filter(pk=student_id).filter(school_pk=school_id)
print student.name
print student.marks.score
print student.marks.status
print student.details.address_city
For your current models, it's difficult to query. But you can try writing SQL queries itself. Something like this
Blog.objects.extra(
select={
'entry_count': 'SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id'
},
)
Follow this
https://docs.djangoproject.com/en/2.1/ref/models/querysets/#extra
I am trying to create the proper Django model that could fit the following reqs:
Person Class has 1 to many relations with the Address Class
Person Class has many to many relations with the Group Class
Book Class contains the collections of the Persons and the Groups
This is my code:
class Person(models.Model):
first_name = models.CharField(max_length=15)
last_name = models.CharField(max_length=20)
def __str__(self):
return self.first_name+ ' - ' + self.last_name
class Address(models.Model):
person = models.ForeignKey(Person)
address_line = models.CharField(max_length=200)
def __str__(self):
return self.address_line
class Group(models.Model):
group_name = models.CharField(max_length=12)
persons = models.ManyToManyField(Person)
def __str__(self):
return self.group_name
class Book(models.Model):
record_name = models.CharField(max_length=12)
person = models.ForeignKey(Person )
group = models.ForeignKey(Group )
def __str__(self):
return self.record_name
However it's not correct:
1) A Group can now contain multiple Persons but the Persons do not contain any Group.
I am not sure if I should add to the Person class the following code:
groups = models.ManyToManyField(Group)
2) The Book class now contains only 1 record of Person & Group per Book record.
3) When I added the Foreign Keys to the models, I removed
on_delete tag:
person = models.ForeignKey(Person, on_delete=models.CASCADE())
because it does not compile it, asking for some params.
I know how to make all this for C#, but I am a kinda stucked with this simple task in Python/Django.
1) The ManyToMany field should appear only in one of the models, and by looks of things you probably want it in the Person model.
Its important to understand that the data about the ManyToMany field is saved in a differant table. Django only allows this field to be visable through buth models (so basiclly, choose where it is move convinient).
2)By the look of your structure I will suggest you use a ManyToMany field through a different table. here is an example:
class Activity(models.Model):
name = models.CharField(max_length=140)
description = models.TextField(blank=True, null=True)
class Route(models.Model):
title = models.CharField(max_length=140)
description = models.TextField()
activities_meta = models.ManyToManyField(Activity, through = 'RouteOrdering')
class RouteOrdering(models.Model):
route = models.ForeignKey(Route, on_delete=models.CASCADE)
activity = models.ForeignKey(Activity, on_delete=models.CASCADE, related_name='activita')
day = models.IntegerField()
order = models.IntegerField(default=0)
that way the data is binded to the ManyToMany field