Course Content

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

Django ORM Ninja: Advanced Techniques for Developers

Retrieve Query

We already know how to retrieve all instances using Author.objects.all(). In this chapter, we'll learn how to obtain a specific instance or filter multiple instances based on certain attributes.

filter()

This query returns a new QuerySet containing objects that match the given lookup parameters. In our example, it will return only one Author with id=3.

The equivalent SQL command is SELECT * FROM Author WHERE last_name = 'Clear';

exclude()

Conversely, exclude() returns a QuerySet with objects that do not match the specified parameters. Here, it will include all Authors whose last name isn't "Clear".

The equivalent SQL command is SELECT * FROM author WHERE last_name != 'Clear';

Combine filters

We can also combine filters. For instance, the query above demonstrates how to use multiple lookups, which we will explore more in the next sections.

The equivalent SQL command is SELECT * FROM author WHERE last_name LIKE 'C%' AND first_name != 'Ronald';

get()

To retrieve a specific object, we use the get method, where pk is a "primary key", and it's the same as id.

The equivalent SQL command is SELECT * FROM author WHERE id = 1;

Unlike get(), slicing with filter() doesn't raise an exception if there are no matching results; it simply returns an empty QuerySet.

1. What does Author.objects.filter(last_name="Clear") return in Django?

2. How does the exclude() method in Django differ from filter()?

3. Which query combines multiple filters in Django?

4. What does the get() method do in Django?

5. How does Django's filter() method behave when there are no matching results?

What does Author.objects.filter(last_name="Clear") return in Django?

Select the correct answer

A new QuerySet containing all authors.

An error if no author has the last name 'Clear'.

A new QuerySet containing authors with the last name 'Clear'.

Answers 2 and 3

How does the exclude() method in Django differ from filter()?

Select the correct answer

exclude() updates records, whereas filter() retrieves them.

There is no difference; they perform the same function.

exclude() retrieves records that do not match the given criteria.

exclude() deletes records that match the given criteria.

Which query combines multiple filters in Django?

Select a few correct answers

Author.objects.filter(last_name__startswith="C")

Author.objects.filter(last_name="Clear").exclude(first_name="Ronald")

Author.objects.get(pk=1)

Author.objects.exclude(last_name="Clear").filter(first_name="Ronald")

What does the get() method do in Django?

Select the correct answer

Retrieves a specific instance of a model by its primary key.

Retrieves all instances of a model.

Deletes a specific instance of a model.

Updates a specific instance of a model.

How does Django's filter() method behave when there are no matching results?

Select the correct answer

It raises an exception.

It returns the first instance of the model.

It returns an empty QuerySet.

It creates a new instance.

Everything was clear?

Section 3. Chapter 2

Course Content

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

Django ORM Ninja: Advanced Techniques for Developers

Retrieve Query

We already know how to retrieve all instances using Author.objects.all(). In this chapter, we'll learn how to obtain a specific instance or filter multiple instances based on certain attributes.

filter()

This query returns a new QuerySet containing objects that match the given lookup parameters. In our example, it will return only one Author with id=3.

The equivalent SQL command is SELECT * FROM Author WHERE last_name = 'Clear';

exclude()

Conversely, exclude() returns a QuerySet with objects that do not match the specified parameters. Here, it will include all Authors whose last name isn't "Clear".

The equivalent SQL command is SELECT * FROM author WHERE last_name != 'Clear';

Combine filters

We can also combine filters. For instance, the query above demonstrates how to use multiple lookups, which we will explore more in the next sections.

The equivalent SQL command is SELECT * FROM author WHERE last_name LIKE 'C%' AND first_name != 'Ronald';

get()

To retrieve a specific object, we use the get method, where pk is a "primary key", and it's the same as id.

The equivalent SQL command is SELECT * FROM author WHERE id = 1;

Unlike get(), slicing with filter() doesn't raise an exception if there are no matching results; it simply returns an empty QuerySet.

1. What does Author.objects.filter(last_name="Clear") return in Django?

2. How does the exclude() method in Django differ from filter()?

3. Which query combines multiple filters in Django?

4. What does the get() method do in Django?

5. How does Django's filter() method behave when there are no matching results?

What does Author.objects.filter(last_name="Clear") return in Django?

Select the correct answer

A new QuerySet containing all authors.

An error if no author has the last name 'Clear'.

A new QuerySet containing authors with the last name 'Clear'.

Answers 2 and 3

How does the exclude() method in Django differ from filter()?

Select the correct answer

exclude() updates records, whereas filter() retrieves them.

There is no difference; they perform the same function.

exclude() retrieves records that do not match the given criteria.

exclude() deletes records that match the given criteria.

Which query combines multiple filters in Django?

Select a few correct answers

Author.objects.filter(last_name__startswith="C")

Author.objects.filter(last_name="Clear").exclude(first_name="Ronald")

Author.objects.get(pk=1)

Author.objects.exclude(last_name="Clear").filter(first_name="Ronald")

What does the get() method do in Django?

Select the correct answer

Retrieves a specific instance of a model by its primary key.

Retrieves all instances of a model.

Deletes a specific instance of a model.

Updates a specific instance of a model.

How does Django's filter() method behave when there are no matching results?

Select the correct answer

It raises an exception.

It returns the first instance of the model.

It returns an empty QuerySet.

It creates a new instance.

Everything was clear?

Section 3. Chapter 2