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Lära ForeignKey Arguments | Relations
Django ORM Ninja: Advanced Techniques for Developers

bookForeignKey Arguments

To define a Many-to-One relation, models.ForeignKey is used. The first argument corresponds to the model to relate to, and the second, 'on_delete', specifies the behavior when the related object is deleted. The options include:

  • CASCADE: deleting a genre deletes all associated books;
  • PROTECT: prevents deletion if there are related books;
  • SET_NULL: sets the genre to Null if null=True in model definition;
  • SET_DEFAULT: sets a default value if the genre is deleted if there available some default value;
  • DO_NOTHING: no action, but may lead to IntegrityError.

The related_name argument in ForeignKey is useful for reverse relation from the Genre 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 (Genre.book_set.all()).

In our case works:

biography.books.all()  # provides all books of the given genre

Book.objects.filter(genre__format="history") # retrieve all books of the given genre

This structure provides a clear understanding of the Many-to-One relationship in Django, showcasing how to define and utilize it effectively.

1. What does 'models.ForeignKey' do in a Django model?

2. What happens when 'on_delete=models.CASCADE' is set in a ForeignKey relationship?

3. What is the purpose of the 'related_name' argument in a ForeignKey field?

question mark

What does 'models.ForeignKey' do in a Django model?

Select the correct answer

question mark

What happens when 'on_delete=models.CASCADE' is set in a ForeignKey relationship?

Select the correct answer

question mark

What is the purpose of the 'related_name' argument in a ForeignKey field?

Select the correct answer

Var allt tydligt?

Hur kan vi förbättra det?

Tack för dina kommentarer!

Avsnitt 4. Kapitel 2

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bookForeignKey Arguments

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To define a Many-to-One relation, models.ForeignKey is used. The first argument corresponds to the model to relate to, and the second, 'on_delete', specifies the behavior when the related object is deleted. The options include:

  • CASCADE: deleting a genre deletes all associated books;
  • PROTECT: prevents deletion if there are related books;
  • SET_NULL: sets the genre to Null if null=True in model definition;
  • SET_DEFAULT: sets a default value if the genre is deleted if there available some default value;
  • DO_NOTHING: no action, but may lead to IntegrityError.

The related_name argument in ForeignKey is useful for reverse relation from the Genre 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 (Genre.book_set.all()).

In our case works:

biography.books.all()  # provides all books of the given genre

Book.objects.filter(genre__format="history") # retrieve all books of the given genre

This structure provides a clear understanding of the Many-to-One relationship in Django, showcasing how to define and utilize it effectively.

1. What does 'models.ForeignKey' do in a Django model?

2. What happens when 'on_delete=models.CASCADE' is set in a ForeignKey relationship?

3. What is the purpose of the 'related_name' argument in a ForeignKey field?

question mark

What does 'models.ForeignKey' do in a Django model?

Select the correct answer

question mark

What happens when 'on_delete=models.CASCADE' is set in a ForeignKey relationship?

Select the correct answer

question mark

What is the purpose of the 'related_name' argument in a ForeignKey field?

Select the correct answer

Var allt tydligt?

Hur kan vi förbättra det?

Tack för dina kommentarer!

Avsnitt 4. Kapitel 2
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