Скачать или смотреть Resolving the Automapper: Missing Type Map Configuration Exception in .NET Web API

Learn how to fix the `Automapper` exception in your .NET Web API when mapping from entities to DTOs, improving your API's functionality and enhancing data retrieval.
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This video is based on the question https://stackoverflow.com/q/69303496/ asked by the user 'Alex Ivan' ( https://stackoverflow.com/u/7727710/ ) and on the answer https://stackoverflow.com/a/69303618/ provided by the user 'Munzer' ( https://stackoverflow.com/u/3692034/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Automapper: Missing Type Map Configuration Exception

When working with a .NET Web API, developers commonly use Automapper to streamline the mapping between domain classes and Data Transfer Objects (DTOs). However, encountering the error "Automapper: Missing type map configuration or unsupported mapping" can hinder the progress of your project. This guide aims to clarify the causes of this error and provide a comprehensive solution.

The Scenario

Imagine you are implementing an API to retrieve a list of Counties based on Countries. While making a GET request for Counties, you faced the Automapper exception. This likely arose from a mismatch in how your data was being processed.

Your domain class for Counties looks like this:

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

And the corresponding DTO is:

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

The Mapping Profile

In your mapping profile, you have correctly set up the mapping:

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

The Service Method

In your service class, you have a method intended to fetch and map the list of counties as follows:

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

At this point, the issue arises because the mapping is being attempted on a task instead of an actual list of counties.

Solution: Await Your Asynchronous Call

To resolve the exception, you need to ensure that you wait for the asynchronous operation to complete. Modify your GetAllAsync method as follows:

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

Key Changes

Use await: By adding await, you make sure that counties contains the actual fetched list of counties instead of a Task.

Correct Mapping: Now that counties contains the list, Automapper can successfully create the map.

Conclusion

In dealing with mapping in .NET Web APIs using Automapper, ensuring that your asynchronous calls are awaited is crucial. By following the aforementioned adjustments, you can effectively resolve the "Missing type map configuration or unsupported mapping" error, allowing your API to function smoothly and retrieve the desired data.

Always remember, Automapper requires fully-realized objects to perform its magic – an important lesson when working with asynchronous data access. Happy coding!