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Вивчайте 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

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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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What does the following annotation query accomplish?

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