How can you access related models or fields through Django ORM?

In Django ORM, access to related models is done through relation fields such as ForeignKey, OneToOneField, and ManyToManyField.

• To access a related object via ForeignKey or OneToOneField, use the attribute with the field's name:

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    title = models.CharField(max_length=100)

book = Book.objects.get(id=1)
author = book.author  # access to the related Author object

• For reverse access (from the parent model to related objects), use the attribute with the suffix _set by default or related_name if specified:

author = Author.objects.get(id=1)
books = author.book_set.all()  # all books of the author

• For ManyToManyField, access to related objects is also through the field attribute:

class Student(models.Model):
    name = models.CharField(max_length=100)

class Course(models.Model):
    students = models.ManyToManyField(Student)

course = Course.objects.get(id=1)
students = course.students.all()  # all students of the course

Thus, access to related models in Django ORM is done through attributes corresponding to relation fields and QuerySet methods for working with multiple relations.