Question

The get_object_or_404() function should also be used in the new_entry() and edit_entry() views. Make this change, test it by entering a URL like http://localhost:8000/new_entry/99999/, and check that you see a 404 error.

Short answer

Replace object retrievals with `get_object_or_404()` and test with a non-existent entry URL.

Step-by-step solution

Understand the task

The task requires using the `get_object_or_404()` function in the `new_entry()` and `edit_entry()` views to handle scenarios where an object is not found. This will ensure a 404 error is returned when a non-existent entry is requested.

Identify the placeholders

Locate instances within `new_entry()` and `edit_entry()` views where you retrieve objects from the database. Typically, this is done using functions like `Model.objects.get()`. These lines will be replaced with `get_object_or_404()`.

Implement get_object_or_404()

In both `new_entry()` and `edit_entry()` views, replace lines where objects are retrieved from the database (like `Model.objects.get(id=entry_id)`) with `get_object_or_404(Model, id=entry_id)`. This function will try to retrieve the object and if not found, raise a 404 error.

Test the implementation

Run the Django server and access a URL with an ID that does not exist, such as `http://localhost:8000/new_entry/99999/`. Ensure that a 404 error page is displayed, verifying the functionality of the `get_object_or_404()` function.

Key concepts

get_object_or_404() function

The `get_object_or_404()` function is a helpful utility provided by Django designed to retrieve an object from your database or raise a 404 error if the object does not exist. Instead of manually querying the database and handling exceptions when an object isn't found, this function simplifies your code and ensures consistent error handling.

How it works is quite straightforward:

• It attempts to retrieve the specified object using the same logic as the standard `Model.objects.get()` function.
• If the object is found, it is returned and processing continues as usual.
• If the object cannot be found, it automatically raises a `Http404` exception, informing the user that the requested resource is unavailable.

You use this function by replacing your existing database retrieval line (e.g., `Model.objects.get(id=entry_id)`) with `get_object_or_404(Model, id=entry_id)`. This minor modification leads to more robust and readable code, and you no longer need to write additional try-except blocks for your queries.

Django views

Django views play a pivotal role in the overall architecture of a Django web application. They are responsible for handling requests from users, processing any necessary information, and returning a response.

A Django view can be a function or a class that processes requests. It takes a web request and returns a web response, which could be anything from an HTML template to a JSON object.

• Views coordinate with models and templates to serve the right content.
• They handle any input validation and authentication that may be required.
• They might also determine which templates to render and with what context data.

For better handling of requests that don't match existing resources, you can employ functions like `get_object_or_404()` in your views. In essence, views are the middle layer within the MVC structure of Django, taking care of the application's logic.

404 error handling

Handling 404 errors is an important aspect of user experience in web applications. A 404 error indicates that the requested resource could not be found on the server, and it's essential to manage these errors gracefully.

When you implement error handling like 404 errors correctly, it can:

• Improve the user experience by providing helpful error pages that guide users back to workable parts of your site.
• Reduce the frustration customers might experience when they reach dead-ends.
• Help webmasters diagnose and fix broken links or missing resources quickly.

In Django, you can manage 404 errors by customizing the `404.html` template. When a `get_object_or_404()` raises a `Http404` exception, Django looks for a `404.html` template in your templates folder to display an appropriate error message. Customizing this page allows a more user-friendly approach to error handling, providing better navigation aids and potentially retaining the user's interest.