I want to access parent model fields using child model object in django

Question

Hello guys I have one query in my Django project. First of all, You can see that I have two Django models named BookSeller and Book

Bookseller model

class BookSeller(models.Model):
    user_name = models.CharField(max_length=200)
    user_email = models.CharField(max_length=200)
    user_password = models.CharField(max_length=200)
    user_phone = models.CharField(max_length=100)
    user_photo = models.ImageField(upload_to='book/seller_photos/%Y/%m/%d/', blank=True)
    user_address = models.CharField(max_length=300)
    user_state = models.CharField(max_length=100)
    user_city = models.CharField(max_length=100)

    def __str__(self):
        return self.user_name

Book Model

class Book(models.Model):
    book_owner = models.ForeignKey(BookSeller, related_name='book_seller', on_delete=models.CASCADE)
    book_category = models.CharField(max_length=200) 
    book_title = models.CharField(max_length=200)
    book_price = models.IntegerField()
    book_edition = models.CharField(max_length=200)
    book_author = models.CharField(max_length=200)
    book_old = models.IntegerField()
    book_page = models.IntegerField()
    book_description = models.TextField(max_length=200)
    book_image_1 = models.ImageField(upload_to='book/book_photos/%Y/%m/%d', blank=True)
    book_image_2 = models.ImageField(upload_to='book/book_photos/%Y/%m/%d', blank=True)
    book_image_3 = models.ImageField(upload_to='book/book_photos/%Y/%m/%d', blank=True)
    book_image_4 = models.ImageField(upload_to='book/book_photos/%Y/%m/%d', blank=True)

    def __str__(self):
        return self.book_title

Want to DO: In my project I want to find books by that book seller's city. For example, if I write city name 'Silicon Valley' in my search field then it should show me all "Books" that's Sellers(BookSeller) belonging to Silicon Valley.

Query: So my query is how can I do that Django Query set, because I can't find out any query which can do this task.

If you guys have any other solution then please suggest me!!!

Answer 1

You can do that like this

Book.objects.filter(book_owner__user_city="Silicon Valley")

and you learn more about various kinds of joining at this link

Answer 2

For finding the books by some book seller's city you can simly filter the Book instances like so:

Book.objects.filter(book_owner__user_city="Silicon Valley")

One other problem I noticed is that I think you misunderstand related_name attribute in ForeignKey .

The related_name attribute specifies the name of the reverse relation from the BookSeller model back to Book model.

If you don't specify a related_name, Django automatically creates one using the name of your model with the suffix _set.

For instance more appropriate related name in your FK would be books , and without defining it would default to book_set .

book_owner = models.ForeignKey(BookSeller, related_name='books', on_delete=models.CASCADE)

Here is an example, lets assume you have 1 instance of BookSeller and 2 isntances of Book with FK to that instance of BookSeller.

my_book_seller = BookSeller(...)
my_book_1 = Book(book_owner=my_book_seller, ...)
my_book_2 = Book(book_owner=my_book_seller, ...)

Now in your case doing the my_book_seller.book_seller.all() (since you defined the related_name to be book_seller ) would return you the two Book instances belonging to my_book_seller . This doesn't make much sense. On the other hand having the related_name='books' you would get the same books by doing my_book_seller.books.all() .

You can find more info in docs .

Answer 3

You can get the desired results doing something like

books_by_seller_city = Book.objects.filter(book_owner__user_city='Silicon Valley')

Note the use of __ which tells the ORM to look at the referenced model attribute.

Answer 4

You can do with q look ups also, in that case you can add more fields in your query.

queryset = Book.objects.filter(Q(book_owner__user_city__icontains=query)|
    .................)