Mapping Properties in Automapper Without Losing Data: A Guide for ASP.NET Core

Learn how to efficiently map properties from `ExamEditVm` to `Exam` using Automapper in ASP.NET Core while preserving existing properties.
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Mapping Properties in Automapper Without Losing Data: A Guide for ASP.NET Core

When developing applications with ASP.NET Core, you often deal with various data models and view models. A common challenge arises when you need to update an existing object with new data from a view model while retaining the properties that were not included in the update. In this guide, we will explore how to effectively use Automapper to achieve this functionality in your application, particularly when handling updates on entities in a Clean Architecture setup.

Understanding the Problem

Consider a scenario where you have an Exam entity that represents a school exam, and an ExamEditVm view model used for submitting edits to the exam data. The Exam entity holds various properties, some of which may not be updated during every edit action. When you attempt to map the view model to the entity directly with Automapper, you unintentionally create a new instance. This results in the loss of any existing values for properties that were not included in the view model.

Here’s a brief overview of our entities and view models for clarity:

The Exam Entity

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

The ExamEditVm View Model

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

The Solution: Update Existing Object Properties with Automapper

To ensure that you are updating the existing exam object without losing any of its unmapped properties, you'll want to use the Map method overload that takes both the source and target objects as parameters. Here's how to implement this correctly:

Step 1: Modify Your Mapping Logic

Instead of creating a new instance of the Exam, modify the existing one by applying the changes from the ExamEditVm model to the already fetched exam object. Here's how the method should look:

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

Key Points

Preserve Existing Data: Using _mapper.Map(model, exam); retains all existing properties in the exam object that are not present in the ExamEditVm model.

Efficiency: You avoid the overhead of creating a new instance, which is crucial for performance in larger applications.

Maintain Clean Architecture: This approach aligns well with Clean Architecture principles by keeping your business logic separate from your data access layer.

Conclusion

Managing object properties during updates can be tricky, but with Automapper, you can streamline this process effectively. By using the proper mapping technique that updates existing instances rather than creating new copies, you ensure that your application maintains its integrity and performs efficiently.

Whether you are building an ASP.NET Core application for educational purposes or any other domain, understanding and mastering Automapper will significantly enhance your development workflow. Remember, using the overload that allows you to specify both the source and destination objects is key to keeping your existing properties intact.

By following these best practices, you can handle updates smoothly and enhance the user experience of your application.