Resolving AutoMapperMappingException in ASP.NET Core Web API

Discover how to fix the `AutoMapper.AutoMapperMappingException` error in your ASP.NET Core Web API when working with Identity DB Context and AutoMapper.
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This video is based on the question https://stackoverflow.com/q/73171846/ asked by the user 'Ayobamilaye' ( https://stackoverflow.com/u/9037515/ ) and on the answer https://stackoverflow.com/a/73192127/ provided by the user 'Rena' ( https://stackoverflow.com/u/11398810/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing AutoMapperMappingException in ASP.NET Core Web API

When developing an ASP.NET Core Web API, encountering errors can be frustrating, especially when they involve mapping configurations. One common issue is the AutoMapper.AutoMapperMappingException, which can arise due to missing type map configuration or unsupported mappings. In this guide, we will explore a specific scenario involving Identity DB Context and AutoMapper, and how to resolve this error swiftly.

The Challenge: Mapping Exceptions in AutoMapper

In our situation, we have two model classes, ApplicationUser and Merchant, along with a Data Transfer Object (DTO) called MerchantCreateDto. The goal is to map these DTOs to our models for creating new merchants in the system. Below is a summary of the vital components involved in this scenario:

Models

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Data Transfer Object (DTO)

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Mapping Configuration

Initially, the mapping was set up as follows:

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The Error Encountered

When an insert operation was performed using a POST request via Postman, the error message returned was:

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Identifying the Problem

The underlying issue stemmed from the fact that there was no defined mapping between the MerchantCreateDto and the ApplicationUser. AutoMapper requires explicit mapping configurations for each type you intend to map. In this case, while MerchantCreateDto was mapped to Merchant, there was no corresponding mapping for ApplicationUser, which caused the application to throw an exception.

The Solution: Adding Missing Type Map Configuration

To resolve this error, we simply need to add the missing mapping configuration. Here’s how to do it correctly:

Updated Mapping Configuration

Add the following line to your mapping profile:

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Complete Mapping Code

Your complete mapping setup should look like this:

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With this additional line, AutoMapper will now know how to map between MerchantCreateDto and ApplicationUser, thus eliminating the AutoMapperMappingException error.

Conclusion

By ensuring that you have proper mappings set up for all necessary types, you'll avoid the AutoMapper.AutoMapperMappingException and streamline your data handling in ASP.NET Core Web API. Always remember to review your mappings if you encounter issues, and consider implementing them in a central mapping profile for better organization and maintainability.

Happy coding!

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