ForeignKey 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?
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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?
Grazie per i tuoi commenti!
