Resolving Fluent Validation with MediatR in ASP.NET Core 3.1 Without StructureMap

Описание: Learn how to properly configure Fluent Validation with MediatR in your .NET Core microservices without StructureMap, including troubleshooting common errors based on Dependency Injection.
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This video is based on the question https://stackoverflow.com/q/63216905/ asked by the user 'Rahul' ( https://stackoverflow.com/u/9043674/ ) and on the answer https://stackoverflow.com/a/63217517/ provided by the user 'Alexander' ( https://stackoverflow.com/u/7775908/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting Fluent Validation with MediatR in ASP.NET Core 3.1

Building microservices with ASP.NET Core 3.1 can be a challenge, especially when integrating powerful libraries like Fluent Validation and MediatR. A frequent question amongst developers is how to successfully use Fluent Validation with MediatR without relying on additional frameworks such as StructureMap. If you've been struggling with this issue, you're not alone. Let's dive into the solution.

Understanding the Problem

The goal is to inject Fluent Validation into your .NET Core microservice alongside MediatR for handling messages and commands. However, many developers face issues when trying to resolve a collection of validators during dependency injection (DI), typically encountering the following error message:

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This issue arises when the framework cannot correctly instantiate the validator due to a misconfiguration in your DI setup.

The Right Configuration

To integrate Fluent Validation with MediatR successfully, you must ensure that your DI configuration in the Startup.cs is set up correctly. Here’s a step-by-step guide to rectify the common points of failure.

Step 1: Add Required NuGet Packages

First, ensure that you have installed the necessary NuGet packages in your project:

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Step 2: Update Startup.cs Configuration

Your Startup.cs should look similar to the following to properly setup Fluent Validation and MediatR:

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Step 3: Register MediatR and the ValidatorBehavior

Make sure you've correctly registered MediatR and your custom ValidatorBehaviour like so:

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Step 4: Modify the ValidatorBehaviour Class

This is a critical step! Instead of using an array to accept the validators, you should use IEnumerable<IValidator<TRequest>>. Here is the corrected code:

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Conclusion

By ensuring the proper DI configuration and modifying the ValidatorBehaviour to accept IEnumerable, you can resolve the issue of injecting Fluent Validation into MediatR in your .NET Core 3.1 applications. This simple fix will save you time and headaches while allowing you to maintain robust validation practices in your microservices.

If you encounter any further issues or have additional questions, feel free to reach out!