I want to query a table with foreign key. Is it possible to replace the foreign key to its value and convert it to dictionary?
Model.py
class Category(models.Model):
name = models.CharField(max_length=40)
class Item(models.Model):
name = models.CharField(max_length=50)
category = models.ForeignKey(Category)
Views.py
dic = {}
dic["data"] = list(Item.objects.all().values())
It is not clear what you are looking for. But I understand that you need a result where instead of ID you get the name of category.
There are two approach. First and better is to change your models as:
class Category(models.Model):
name = models.CharField(max_length=40)
def __str__(self):
return str(self.name)
This is a better method using this you do not have add an extra line requesting name of category each time.
Another is to query in this manner:
Item.objects.all().values('name', 'category__id')
Related
Suppose in a relational database schema we have a student, a subject and a teacher which connect to each other with a relation teaches. Also, the relation has an attribute time that stores the time of the lesson. This is the most complete yet simplified example I can think to describe my case. Now, the most pythonic and django-wise way I can think of trying to reach a correct solution is, after creating a model class for student, subject and teacher, to create a new class Teaches, which has the foreign keys for the three other classes; also it has the property date field for time. This class would look something like this:
class Teaches(models.Model):
teachers = models.ForeignKey(Teacher, on_delete_models.CASCADE)
subjects = models.ForeignKey(Subject, on_delete_models.CASCADE)
students = models.ForeignKey(Student, on_delete_models.CASCADE)
time = models.DateField
class Meta:
constraints = [
fields=['teachers', 'subjects', 'students']
name='teacher_subject_student_triplet'
]
I added the Meta class because this is what this answer recommends as the correct approach.
The problem is that that in the migrations file I can still see the id field. The only way I've seen there is to remove it is to set another field as Primary Key, but in my case I cannot do that, having more than one keys. Any suggestions?
=========== model.py =============
from django.db import models
class TeacherModel(models.Model):
teacher_code = models.CharField(max_length=255)
def __str__(self):
return self.teacher_code
class SubjectModel(models.Model):
subject_code = models.CharField(max_length=255)
def __str__(self):
return self.subject_code
class StudentModel(models.Model):
student_code = models.CharField(max_length=255)
def __str__(self):
return self.student_code
class Teaches(models.Model):
custom_primary_key = models.SlugField(primary_key=True,blank=True)
teacher = models.ForeignKey(TeacherModel, on_delete=models.CASCADE)
subject = models.ForeignKey(SubjectModel, on_delete=models.CASCADE)
student = models.ForeignKey(StudentModel, on_delete=models.CASCADE)
time = models.DateField
#property
def make_key(self):
new_key = str(self.teacher.teacher_code + self.subject.subject_code + self.student.student_code)
return new_key
def save(self, *args, **kwargs):
self.custom_primary_key = self.make_key
super(Teaches, self).save(*args, **kwargs)
========= Output ==============
You can remove autogenerated id by adding primary_key=True, see below code:
class Person(models.Model):
username = CharField(primary_key=True, max_length=100)
first_name = CharField(null=True, blank=True, max_length=100)
setting a field to primary_key=True automatically makes it unique and not null.
In settings.py:
DEFAULT_AUTO_FIELD = 'django.db.models.BigAutoField'
Controls the automatic generation of primary keys of each model if defined in settings.
Read this article:
Set AutoField or BigAutoField on a per model basis
I have some categories that I can filter them by primary key like this :
p=product.objects.filter(category=2)
but I do not want to bother my self with primary keys I want to filter with exact name of the category not primary key.
I have categories like this :
image
is there a way to use something like p=product.objects.filter(category=home) ?
models:
class category(models.Model):
name=models.CharField(max_length=255, db_index=True)
def __str__(self):
return self.name
class product(models.Model):
category = models.ForeignKey(category, related_name='products',on_delete=models.CASCADE)
image=models.CharField(max_length=500)
description=models.CharField(max_length=500)
price=models.CharField(max_length=50)
buy=models.CharField(max_length=100)
You can .filter(…) [Django-doc] with:
product.objects.filter(category__name='home')
Note: Models in Django are written in PascalCase, not smallcase,
so you might want to rename the model from product to Product.
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.
How can I can use managers to query my foreign key and then retrieve objects that are connected to foreign key?
Here is my models.py:
from django.db import models
# Create your models here.
class BookManager(models.Manager):
def title_count(self,keyword):
return self.filter(title__icontains=keyword).count()
class CategoryManager(models.Manager):
def category_count(self):
return self.filter(category__icontains=python).count()
class Category(models.Model):
title=models.CharField(max_length=20)
def __str__(self):
return self.title
class Enquiry(models.Model):
title=models.CharField(max_length=200)
category=models.ForeignKey(Category ,default=False,blank=False)
detail=models.TextField()
objects = BookManager()
objects=CategoryManager()
# tags=models.ChoiceField()
def __str__(self):
return self.title
I tried to use category manager but it gave me a strange error.
I just want to know how exactly we can get the objects that are connected with category foriegn-key and show them as list to the users.
You can combine both the title_count and category_count methods under one Manager. When filtering through a ForeignKey, your field lookup needs to specify the name of the field you're trying to filter on, else it will assume you're querying the ID field. So instead of category__icontains, you would do category__title__icontains.
Another note, in newer versions of Django, you are required to specify the on_delete parameter when defining a ForeignKey.
This is a working example of what I think you're trying to accomplish.
class BookManager(models.Manager):
def title_count(self, keyword):
return self.filter(title__icontains=keyword).count()
def category_count(self, keyword):
return self.filter(category__title__icontains=keyword).count()
class Category(models.Model):
title = models.CharField(max_length=20)
def __str__(self):
return self.title
class Enquiry(models.Model):
title = models.CharField(max_length=200)
category = models.ForeignKey(Category,
default=False,
blank=False,
on_delete=models.CASCADE)
detail = models.TextField()
books = BookManager()
# tags=models.ChoiceField()
def __str__(self):
return self.title
Here's how you would use it:
Enquiry.books.category_count('python')
Enquiry.books.title_count('test')
I am creating a class in Django's models.py. When I am creating a second class where I have a foreign key from the first class. The key is "1" or "2" or ...
I wonder if you can set up Django to use a specific field to use as key.
For example:
class Customer(models.Model):
name = models.CharField(max_length=64)
myid = models.CharField(max_length=64)
class Setting(models.Model):
owner = models.ForeignKey(Customer)
...
Then I have a view
def getsetting(request):
response = serializers.serialize('json', Setting.objects.all())
return HttpResponse(response, content_type='json')
The json returned shows "1", "2", ... as key for the field "owner".
So my question is, if I could use "name" or "myid" as foreign key? Or is there a simple way to overwrite these field in the json?
Thanks!
"If you’d like to specify a custom primary key, just specify primary_key=True on one of your fields." https://docs.djangoproject.com/en/1.4/topics/db/models/#automatic-primary-key-fields
So, you can change your class Customer:
class Customer(models.Model):
name = models.CharField(max_length=64)
myid = models.CharField(primary_key=True, max_length=64)
Take a look at serialization with natural keys. You can read the official docs here: https://docs.djangoproject.com/en/1.7/topics/serialization/#natural-keys
It is fairly simple, just add a method to your class:
class Customer(models.Model):
name = models.CharField(max_length=64)
myid = models.CharField(max_length=64)
def natural_key(self):
return (self.myid, )
And then serialize with use_natural_foreign_keys=True:
def getsetting(request):
response = serializers.serialize('json', Setting.objects.all(),
use_natural_foreign_keys=True)
return HttpResponse(response, content_type='json')