Resolving the Empty List Issue in ASP.NET Core MVC Repository Patterns

Discover how to prevent your list from becoming empty after adding items in an ASP.NET Core MVC application by correctly using dependency injection in your controller.
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Understanding the Empty List Problem in ASP.NET Core MVC

As burgeoning developers dive into the world of ASP.NET Core MVC, encountering challenges is part of the learning journey. One common issue is the unexpected behavior of data collections, particularly when working with repositories. In this guide, we’ll tackle the problem of an empty list every time an item is added to it within a controller. This situation can be quite frustrating, but understanding the underlying principles of dependency injection (DI) and object lifecycle management will lead to a solution.

The Scenario

Problem Description

You have created a HomeController in ASP.NET Core MVC, which is designed to handle job management. The controller contains two methods: one for adding a job and another for retrieving all jobs. While the controller receives data successfully, the issue arises when the data is stored in a JobRepository. Every time a job is added, the list that is supposed to hold jobs appears empty on subsequent requests. Here’s a simplified view of the code:

[[See Video to Reveal this Text or Code Snippet]]

The core of the problem lies in how the JobRepository is initialized each time the HomeController instance is created.

Solution: Implementing Dependency Injection Properly

The Issue with Current Implementation

In your current setup, each time a request is made, a new instance of JobRepository is created within the HomeController, resulting in a fresh list that holds no previously added jobs. This approach effectively ignores the DI container's lifecycle management, which is critical in ASP.NET Core applications. Consequently, the list resets on every new instantiation of the controller.

Constructing the HomeController with Dependency Injection

To maintain the job list's state across multiple requests, you should use ASP.NET Core's built-in dependency injection. Here’s how to refactor your HomeController:

[[See Video to Reveal this Text or Code Snippet]]

Explanation:

Injecting the Repository: By accepting an instance of IJobRepository (which is a good practice as it promotes loose coupling), the controller uses a single instance of JobRepository throughout the application's lifecycle.

Null Check: The added null check ensures that a valid repository instance is always provided, enhancing robustness.

Registering the JobRepository in Startup

[[See Video to Reveal this Text or Code Snippet]]

This registration tells the DI container to provide the same instance of JobRepository for each request, meaning data in the jobs list is preserved.

Conclusion

By reconfiguring how your HomeController handles the JobRepository, you've solved the empty list problem. Utilizing dependency injection not only keeps your list intact but also aligns with best practices in ASP.NET Core applications. This refactoring ensures that your application will behave as expected, providing a more stable and robust experience as you continue your journey in web development with ASP.NET Core MVC.

Key Takeaways

Always use DI to manage object lifetimes in ASP.NET Core.

Validate injected dependencies with null checks.

Understand the impact of lifecycle (transient, scoped, singleton) on application behavior.

This small adjustment can significantly enhance the sustainability of your application and improve its performance and reliability. Keep experimenting and learning!