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Aprenda Annotations | Complex Queries
Django ORM Ninja: Advanced Techniques for Developers
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Django ORM Ninja: Advanced Techniques for Developers

Django ORM Ninja: Advanced Techniques for Developers

1. Introduction to Django ORM
2. Models, datatypes, and fields
3. Queries
4. Relations
5. Complex Queries
6. Advanced

book
Annotations

Annotation in Django ORM allows you to attach additional information to each object in a QuerySet. It's a powerful feature for augmenting the results of queries with calculated values, which can be aggregates computed over related objects or values derived from model fields.

Basic Annotation

Example 1:

Assume each Book has a pages field. This annotates each genre with the total number of pages of all books within that genre.

python

Example 2:

Assume each Book has a rating field.

python

Adds an average rating for the books written by each author.

Advanced Annotation Use Cases

Example 1:

Assume each Book has a publication_date field.

python

Counts how many books each author published per year.

Example 2:

Finds the most recently published book for each genre.

python

Annotation with Filters

Example 1:

Counts the number of fantasy books written by each author.

python

1. What is the primary purpose of annotation in Django ORM?

2. What does the following annotation query accomplish?

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What is the primary purpose of annotation in Django ORM?

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question mark

What does the following annotation query accomplish?

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