How to Rename Items in values() in Django?

In Django, the values() method of a QuerySet is a powerful tool that allows us to return a subset of fields from the database. This is especially useful when we need only specific columns from a model and don't require the entire model instance. A noteworthy feature of the values() method is its ability to rename fields in the output, making data manipulation and presentation more straightforward. In this article, we'll explore how to effectively rename fields using the values() method in Django, accompanied by a mini project.

Rename Items in values() in Django

Let's set up a small Django project to demonstrate renaming fields using the values() method. Our example project will be a simple book management system.

Step 1: Setting Up the Django Project

First, ensure Django is installed. If not, we can install it via pip:

pip install django

Create a new Django project and an application:

django-admin startproject BookManager
cd BookManager
python manage.py startapp books

Step 2: Defining the Model

In the books app, we'll create a simple Book model. Open books/models.py and define the model as follows:

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=255)
    author = models.CharField(max_length=255)
    published_date = models.DateField()

    def __str__(self):
        return self.title

Add the books app to the INSTALLED_APPS list in BookManager/settings.py:

INSTALLED_APPS = [
    ...
    'books',
]

Step 3: Migrating the Database

Run the following commands to create the database tables:

python manage.py makemigrations books
python manage.py migrate

Step 4: Using values() to Rename Fields

We will now use Django’s interactive shell to demonstrate renaming fields using values(). Start the shell:

python manage.py shell

Inside the shell, follow these steps to create some book entries and then use values() with field renaming:

from books.models import Book
from datetime import date

# Create some book entries
Book.objects.create(title="Django for Beginners",
                    author="William S. Vincent", published_date=date(2018, 9, 1))
Book.objects.create(title="Two Scoops of Django",
                    author="Daniel and Audrey Roy Greenfeld", published_date=date(2021, 4, 1))

books = Book.objects.values('title', 'author')

# Display the results with renaming in the loop
for book in books:
    print({
        'book_title': book['title'],
        'writer': book['author']
    })

In this example, values() is used to select and rename the title and author fields to book_title and writer, respectively.

Explanation

• QuerySet values() Method: When we call values() on a QuerySet and pass keyword arguments where keys are new names and values are existing model fields, Django renames the fields in the resulting dictionary.

This feature is particularly useful in scenarios where the field names in the database are not intuitive or when the frontend requires specific key names.

Output:

Conclusion

Renaming fields directly in the values() method simplifies data processing and reduces the need for additional steps in data manipulation. This can be especially beneficial in projects involving data APIs or when preparing data for frontend frameworks. Django's ability to handle these transformations efficiently at the database level showcases its robustness and flexibility in managing database queries.

sagar99

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Article Tags :

• Python
• Python Django

Practice Tags :

• python