How to Fix ASP.NET Core DTO Issues with AutoMapper and Dapper

Discover solutions to common DTO mapping issues in ASP.NET Core applications using AutoMapper and Dapper for seamless data transfer.
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Understanding DTO Issues in ASP.NET Core with AutoMapper and Dapper

In recent projects using ASP.NET Core applications, developers often encounter challenges when using Data Transfer Objects (DTOs) alongside libraries like AutoMapper and Dapper. These problems can lead to confusing scenarios where the expected data is not returned correctly, particularly when using Swagger for API testing. This guide aims to clarify these issues and provide a robust solution to help you effectively implement DTOs in your applications.

The Problem: Missing Data in DTOs

One of the most common issues developers face is when the fields in the DTO remain null even though the data exists in the database. Let's take a look at a practical scenario.
You have a class structure that looks like this:

Response Class: Encapsulates response data and metadata.

Employee Class: Represents the employee model fetched from the database.

EmployeeDto: This DTO is intended to transfer employee data with a different structure.

When calling your endpoint, you discover that fields of EmployeeDto appear as null upon querying the database records through Swagger. This creates confusion as data in the underlying model (e.g., Employee) exists.

An Example of the Code Structure

Your structure may look like the following:

Response Class

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

Employee Class

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

Employee Mapper Profile

Configuring mapping between your model and DTO:

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

The Solution: Proper Mapping with AutoMapper

To resolve the issue of null fields populating in your EmployeeDto, consider these steps:

Step 1: Properly Inject AutoMapper

Ensure that AutoMapper is injected correctly in your repository class as shown below:

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

Step 2: Modify the GetAllEmployeesAsync Method

When you fetch the data, make sure to use the Mapper to convert the retrieved model to a DTO. Here is how you can modify your method:

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

Step 3: Return Mapped Data from the Controller

In your controller, make sure you handle the response correctly to return your DTO data to the consumer of the API:

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

Conclusion

By following the steps outlined above, you can effectively utilize AutoMapper with Dapper in your ASP.NET Core applications to ensure that your DTOs are populated correctly with data from your database models. This approach will enhance the reliability of your API responses and result in a better development experience.

If you encounter similar issues, remember to check your mapping configurations and ensure that the data transformation between models and DTOs is set up correctly.