Optimise django query when fetching information from multiple models - django

Question

I am new to Django and using Django 3.0.6.
With the following code, I have been able to achieve the desired results and display detailed book information onto the template. However, on average, ORM makes 8 to 9 database queries to get detailed information about the book. I am looking for expert help to optimize my database queries so that I could fetch book-related information with fewer queries.
I tried using select_related() and prefetch_related() but without any luck, maybe I did it improperly. Is there a scope of using Q object or union(), just my thought? How can I achieve the same results with minimum queries to the database?
Please help me with detailed code, if possible.
models.py
class Publisher(models.Model):
publisher_name = models.CharField(max_length=50)
class Author(models.Model):
author_name = models.CharField(max_length=50)
class Booktype(models.Model):
book_type = models.CharField(max_length=20) # Hard Cover, Soft Cover, Kindle Edition, Digital PDF etc.
class Book(models.Model):
book_title = models.TextField()
slug = models.SlugField(max_length=50, unique=False)
published_date = models.DateField(auto_now=False, auto_now_add=False)
publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE)
author = models.ForeignKey(Author, on_delete=models.CASCADE)
book_type = models.ManyToManyField(Booktype, through='BookPrice', through_fields=('book', 'book_type'))
# I created this separate model due to havy content and to keep Book model light
class BookDetail(models.Model):
a = models.TextField(null=True, blank=True)
b = models.TextField(null=True, blank=True)
c = models.TextField(null=True, blank=True)
book = models.OneToOneField(Book, on_delete=models.CASCADE)
class BookPrice(models.Model):
book_type = models.ForeignKey(Booktype, on_delete=models.CASCADE)
book = models.ForeignKey(Book, on_delete=models.CASCADE)
price = models.DecimalField(max_digits=7, decimal_places=2)
view.py
def get_book_details(request, book_id, slug):
book = Book.objects.get(id=book_id, slug=slug)
context = {'book': book}
return render(request, 'products/book_detail.html', context)
book_detail.html Template
# 1st databse query
{{ book.book_title }}
{{ book.id }}
{{ book.published_date }}
# 2nd databse query
{{ book.publisher.publisher_name }}
# 3rd databse query
{{ book.author.author_name }}
# 4th databse query
{{ book.bookdetail.a }}
{{ book.bookdetail.b }}
{{ book.bookdetail.c }}
# 5th to 9th databse query depending upon avaialble Book Types
{% for x in book.bookprice_set.all %}
{{ x.book_type }} {{ x.price|floatformat }}
{% endfor %}

Answer 1

You can use .select_related(…) [Django-doc] to fetch the publisher, author and bookdetail. We can use prefetch_related
def get_book_details(request, book_id, slug):
book = Book.objects.select_related(
'publisher', 'author', 'bookdetail'
).prefetch_related(
'bookprice_set', 'bookprice_set__book_type'
).get(id=book_id, slug=slug)
context = {'book': book}
return render(request, 'products/book_detail.html', context)