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Annotations | Complex Queries
Django ORM Ninja: Técnicas Avanzadas para Desarrolladores
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Django ORM Ninja: Técnicas Avanzadas para Desarrolladores

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.

Example 2:

Assume each Book has a rating field.

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.

Counts how many books each author published per year.

Example 2:

Finds the most recently published book for each genre.

Annotation with Filters

Example 1:

Counts the number of fantasy books written by each author.

1. What is the primary purpose of annotation in Django ORM?
2. What does the following annotation query accomplish?

What is the primary purpose of annotation in Django ORM?

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What does the following annotation query accomplish?

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¿Todo estuvo claro?

Sección 5. Capítulo 4
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