How can you avoid executing unnecessary queries when working with ORM in Django, especially with related models?

To avoid unnecessary queries when working with ORM in Django, especially with related models, the methods select_related and prefetch_related are used.

• select_related performs an SQL JOIN and loads related objects in a single query. Suitable for ForeignKey and OneToOne relations.

• prefetch_related performs separate queries for related objects and then combines them in Python. Suitable for ManyToMany and reverse relations.

Example:

# Without optimization
books = Book.objects.all()
for book in books:
    print(book.author.name)  # A separate query for each book to author

# With select_related
books = Book.objects.select_related('author').all()
for book in books:
    print(book.author.name)  # One query with JOIN

# With prefetch_related for ManyToMany
authors = Author.objects.prefetch_related('books').all()
for author in authors:
    for book in author.books.all():
        print(book.title)

Using these methods significantly reduces the number of queries and improves performance.