'Missing ApiException' compiler error

Currently I have a project that uses multiple openapi.json v3 files. We used the official openapi tools described in this link: https://docs.microsoft.com/en-us/aspnet/core/web-api/microsoft.dotnet-openapi?view=aspnetcore-3.1

Because of the following code the generated c# client do not compile:

<ItemGroup>
  <!-- @(CurrentOpenApiReference) item group will never contain more than one item. -->
  <CurrentOpenApiReference>
    <Command>$(_NSwagCommand) openapi2csclient /className:%(ClassName) /namespace:%(Namespace)</Command>
  </CurrentOpenApiReference>
  <CurrentOpenApiReference>
    <Command Condition="! %(FirstForGenerator)">%(Command) /GenerateExceptionClasses:false</Command>
  </CurrentOpenApiReference>
  <CurrentOpenApiReference>
    <Command>%(Command) /input:"%(FullPath)" /output:"%(OutputPath)" %(Options)</Command>
  </CurrentOpenApiReference>
</ItemGroup>

Why did you make this design decision of not generating the Exception code for the remaining clients? The commented affirmation of only one item is not true.

I managed it to work by adding a AdditionalNamespaceUsages options but for me it feels like a hack.

Below I added a sample of a csproj to reproduce the issue:

<Project Sdk="Microsoft.NET.Sdk">
  
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>
      
  <ItemGroup> 
    <PackageReference Include="Newtonsoft.Json" Version="12.0.2" /> 
    <PackageReference Include="NSwag.ApiDescription.Client" Version="13.5.0" />
  </ItemGroup>
  
  <ItemGroup>
    <OpenApiReference Include=".\OpenApi1.json">
      <Namespace>Integration.ExternalApi1</Namespace>
    </OpenApiReference>
    
    <OpenApiReference Include=".\OpenApi2.json">
      <Namespace>Integration.ExternalApi2</Namespace>
      <!-- Workaround to make the generated code compile -->
      <!--<Options>/AdditionalNamespaceUsages:Integration.ExternalApi1</Options>-->
    </OpenApiReference>
  </ItemGroup>
  
</Project>

[WizX20]

I stumbled on this one when I had to generate a new version of a client side-by-side.

I had a look at https://github.com/RicoSuter/NSwag/blob/85ae862fd6d68173a201a79e0ad06e0be2ec5de1/src/NSwag.CodeGeneration.CSharp/CSharpClientGeneratorSettings.cs to check the options we have.

Finally, I decided not to use a generated ApiException class, but instead move that to my own file.

1. Move the ApiException partial classes from the first generated client to it’s own ApiException.cs file with the namespace ‘Example.Api.Client.Exceptions’
2. Use the GenerateExceptionClasses:false in the options:

    <OpenApiReference Include="Example.openapi.v1_3.json" CodeGenerator="NSwagCSharp" Namespace="Example.Api.Clients.v1_3" Condition="'$(Configuration)'=='Debug'">
      <OutputPath>..\Clients\Example.openapi.v1_3Client.cs</OutputPath>
      <Options>/GenerateClientInterfaces:true /GenerateExceptionClasses:false /AdditionalNamespaceUsages:Example.Api.Client.Exceptions</Options>
    </OpenApiReference>
    <OpenApiReference Include="Example.openapi.v1_4.json" CodeGenerator="NSwagCSharp" Namespace="Example.Api.Clients.v1_4" Condition="'$(Configuration)'=='Debug'">
      <OutputPath>..\Clients\Example.openapi.v1_4Client.cs</OutputPath>
      <Options>/GenerateClientInterfaces:true /GenerateExceptionClasses:false /AdditionalNamespaceUsages:Example.Api.Client.Exceptions</Options>
    </OpenApiReference>

[iannicktl]

I do have the same issue. Used the following workaround:

1. Create a new file (I named it NSwagClientError_Missing_Code_Generation_Of_ApiException_OnTheSecondClient.cs)
2. Pass the code below
3. Replace the namespace [YourNameSpaceFoNswagGenerateClient] and the class name [YourClassNameForNswagGenerateClient]. The 2 must match what you put on generated NSwag client

Here is the ApiException code

{
    /// <summary>
    /// https://github.com/RicoSuter/NSwag/issues/2839
    /// </summary>
    public partial class [YourClassNameForNswagGenerateClient]
    {

        public partial class ApiException : System.Exception
        {
            public int StatusCode { get; private set; }

            public string Response { get; private set; }

            public System.Collections.Generic.IReadOnlyDictionary<string, System.Collections.Generic.IEnumerable<string>> Headers { get; private set; }

            public ApiException(string message, int statusCode, string response, System.Collections.Generic.IReadOnlyDictionary<string, System.Collections.Generic.IEnumerable<string>> headers, System.Exception innerException)
                : base(message + "\n\nStatus: " + statusCode + "\nResponse: \n" + ((response == null) ? "(null)" : response.Substring(0, response.Length >= 512 ? 512 : response.Length)), innerException)
            {
                StatusCode = statusCode;
                Response = response;
                Headers = headers;
            }

            public override string ToString()
            {
                return string.Format("HTTP Response: \n\n{0}\n\n{1}", Response, base.ToString());
            }
        }

        [System.CodeDom.Compiler.GeneratedCode("NSwag", "13.17.0.0 (NJsonSchema v10.8.0.0 (Newtonsoft.Json v13.0.0.0))")]
        public partial class ApiException<TResult> : ApiException
        {
            public TResult Result { get; private set; }

            public ApiException(string message, int statusCode, string response, System.Collections.Generic.IReadOnlyDictionary<string, System.Collections.Generic.IEnumerable<string>> headers, TResult result, System.Exception innerException)
                : base(message, statusCode, response, headers, innerException)
            {
                Result = result;
            }
        }
    }
}