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Hello everybody, welcome to MVC pattern with Djangol. Today, we will explore the MVC architectural pattern and its application in Django web development. We will also delve into Callbacks and Promises, fundamental concepts for asynchronous programming, and understand their significance in Django. Finally, we will explore real-life examples to solidify these concepts.
The MVC pattern promotes separation of concerns, reusability, and testability. While Django doesn't strictly enforce MVC, it provides tools and conventions to follow it and create well-structured web applications.
The MVC pattern offers a structured approach to web development, promoting cleaner code, efficient reuse of components, and facilitating the creation of robust and maintainable web applications.
This is a simplified example of how MVC separates concerns in a Django application. The controller acts as an intermediary, fetching data from the model and delivering it to the view for presentation.
Callbacks and Promises are essential for managing asynchronous operations, where a program can continue executing without waiting for a long-running task to finish. This is crucial for responsive web applications.
Asynchronous operations are essential for web applications to remain responsive while fetching data or interacting with external resources. Callbacks and Promises provide mechanisms to handle these asynchronous operations effectively.
In Django, we can leverage callbacks to handle asynchronous tasks. These tasks run in the background without blocking the main request-response cycle. There are two main approaches to using callbacks for asynchronous operations in Django:
Asynchronous Tasks with Libraries: Libraries like django.core.signals and Celery allow you to define functions to be executed asynchronously. These tasks can be triggered by events within your Django application, such as a user saving data. When such an event occurs, the library will invoke the predefined callback function to handle the task in the background. This is a powerful approach for handling long-running operations that don't require immediate user interaction.
Django Signals: Django's built-in signal system allows you to connect functions (essentially callbacks) to specific events or signals emitted by the framework itself. For instance, you can define a callback function that gets triggered after a user is saved. This callback can then be used to perform secondary actions like sending an email notification or updating related data. This approach is useful for reacting to framework events and performing additional actions asynchronously.
By effectively using callbacks with asynchronous tasks and signals, we can create responsive and performant Django applications that can handle complex workflows without hindering the user experience.
While Django offers an Object-Relational Mapper (ORM) for simplified database interactions, there might be scenarios where raw SQL queries are necessary. In such cases, libraries like asyncpg come into play. asyncpg enables asynchronous database interactions using callbacks. You can initiate the SQL query and define a callback function to handle the results once they become available. This approach prevents the main thread from being blocked while waiting for the database operation to complete, improving the overall performance and responsiveness of your Django application.
By leveraging callbacks with asynchronous database operations, you can ensure that your Django application remains efficient and maintains a seamless user experience even when interacting with databases.
Traditional synchronous programming involves blocking I/O (Input/Output) operations. The program execution halts until the I/O operation (like reading data from a file or network) finishes.
While callbacks offer a way to handle asynchronous operations, their extensive use can lead to a situation known as "callback hell." This occurs when you have multiple asynchronous operations stacked within one another, using nested callbacks. The resulting code structure becomes convoluted and challenging to understand, debug, and maintain. Imagine a bunch of tangled spaghetti!
To avoid callback hell, it's essential to be mindful of the number of nested callbacks used in your Django application. Consider alternative approaches like Promises or Async/Await (covered in the next slide) for more complex asynchronous workflows. These approaches can provide a clearer and more maintainable way to handle asynchronous operations in your Django code.
For database interactions in Django, you can achieve non-blocking operations using libraries like asyncpg. This avoids freezing the main program while waiting for data. Instead, you define a callback function to handle the results later, allowing the main thread to continue working.

Code repo: https://github.com/dhirajpatra/django...