Visual Studio–Generate C# client for OpenAPI

There are multiple ways to generate a C# client based on an OpenAPI specification file. Today I want to show you how this can be done directly inside Visual Studio.

To import an OpenAPI reference, you can right-click on your project and choose Add –> Service Reference:

Choose OpenAPI from the list of possible service references and click on Next:

Now we can specify the details to our OpenAPI JSON file. Click on Finish to generate the client:

It can take some time to generate the client. So be patient.

What is happening behind the scenes?

Let us have a look at all the things that Visual Studio is doing behind the scenes.

First a copy of the OpenAPI json file is imported into our project and stored inside an OpenAPIs folder:

On this JSON file the build action is set to Open API File Reference and specific code generation attributes are configured:

Our updated csproj file looks like this:

	<Project Sdk="Microsoft.NET.Sdk.Worker">
	<PropertyGroup>
	<TargetFramework>net6.0</TargetFramework>
	</PropertyGroup>
	<ItemGroup>
	<OpenApiReference Include="OpenAPIs\v1.json" CodeGenerator="NSwagCSharp" Namespace="GettingStarted" ClassName="CapakeyClient">
	<SourceUri>https://geo.api.vlaanderen.be/capakey/v2/swagger/docs/v1</SourceUri>
	</OpenApiReference>
	</ItemGroup>
	</Project>

view raw Example.csproj hosted with ❤ by GitHub

Behind the scenes the code generator is using the Microsoft.dotnet-openapi command line tool which uses NSwag in the end.

We can further control what is generated by specifying additional options:

	<ItemGroup>
	<OpenApiReference Include="OpenAPIs\v1.json" CodeGenerator="NSwagCSharp" Namespace="GettingStarted" ClassName="CapakeyClient" Options="/JsonLibrary:SystemTextJson" >
	<SourceUri>https://geo.api.vlaanderen.be/capakey/v2/swagger/docs/v1</SourceUri>
	</OpenApiReference>
	</ItemGroup>

view raw Example.csproj hosted with ❤ by GitHub