Kursinnehåll

Django ORM Ninja: Advanced Techniques for Developers

1. Introduction to Django ORM

Introduction to the Course Introduction to the ORM Start a New Project Initialize a New Project

2. Models, datatypes, and fields

Defining The First Model Field Data Types Define Other Models Migrations Admin Interface

3. Queries

Create Query Retrieve Query Lazy Queries Ordering and Slicing Updating Deleting

4. Relations

Many-to-One ForeignKey Arguments One-to-One Many-to-Many

5. Complex Queries

Field Lookups Q and F Objects Aggregations Annotations Minimazing Database Hints

6. Advanced

Class Meta Constrains Transactions Basics User Model

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.

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 4. Kapitel 2

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Kursinnehåll

Django ORM Ninja: Advanced Techniques for Developers

1. Introduction to Django ORM

Introduction to the Course Introduction to the ORM Start a New Project Initialize a New Project

2. Models, datatypes, and fields

Defining The First Model Field Data Types Define Other Models Migrations Admin Interface

3. Queries

Create Query Retrieve Query Lazy Queries Ordering and Slicing Updating Deleting

4. Relations

Many-to-One ForeignKey Arguments One-to-One Many-to-Many

5. Complex Queries

Field Lookups Q and F Objects Aggregations Annotations Minimazing Database Hints

6. Advanced

Class Meta Constrains Transactions Basics User Model

ForeignKey Arguments

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.

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.

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 4. Kapitel 2

Django ORM Ninja: Advanced Techniques for Developers

ForeignKey Arguments

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?

Django ORM Ninja: Advanced Techniques for Developers

ForeignKey Arguments

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?