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

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

Ordering and Slicing

Slicing

Slicing, like Author.objects.all()[:1], retrieves a QuerySet limited to a specified range.

Remember that slicing on QuerySets, like [:1], is performed at the database level, so it's an efficient way to limit the number of results returned by a query.

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Returns the first two objects (equivalent to LIMIT 2 in SQL).

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Fetches the second and third objects from the table (akin to OFFSET 1 LIMIT 2 in SQL).

Ordering

To sort a QuerySet, use the order_by() method with the attribute name for ordering. Prepend '-' for descending order.

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For ascending order ( SELECT * FROM Author ORDER BY first_name;).

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For descending order ( SELECT * FROM Author ORDER BY first_name DESC;).

To define multiple ordering criteria in one order_by statement:

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(SELECT * FROM Author ORDER BY first_name ASC, last_name DESC;).

1. What does the Django query Author.objects.all()[:1] return?

2. How does Django perform slicing on QuerySets like [:1]?

3. What is the SQL equivalent of Author.objects.all()[:2]?

4. How do you sort a QuerySet in ascending order by the 'first_name' field?

5. Which Django query sorts authors first by ascending 'first_name' and then by descending 'last_name'?

What does the Django query Author.objects.all()[:1] return?

Виберіть правильну відповідь

The first author in the table.

An error, as slicing is not allowed in Django.

The last author in the table.

A random author from the table.

How does Django perform slicing on QuerySets like [:1]?

Виберіть правильну відповідь

At the Python level, after retrieving all records.

At the database level, efficiently limiting the number of results.

By randomly selecting a set number of records.

By deleting all but the first record in the database.

What is the SQL equivalent of Author.objects.all()[:2]?

Виберіть правильну відповідь

SELECT * FROM Author WHERE id < 2

SELECT * FROM Author OFFSET 2

SELECT TOP 2 * FROM Author

SELECT * FROM Author LIMIT 2

How do you sort a QuerySet in ascending order by the 'first_name' field?

Виберіть правильну відповідь

Author.objects.filter('first_name')

Author.objects.sort('first_name')

Author.objects.order_by('first_name')

Author.objects.order_by('-first_name')

Which Django query sorts authors first by ascending 'first_name' and then by descending 'last_name'?

Виберіть правильну відповідь

Author.objects.order_by('-first_name', 'last_name')

Author.objects.order_by('first_name', '-last_name')

Author.objects.order_by('last_name', 'first_name')

Author.objects.sort('first_name', '-last_name')

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