Swashbuckle.AspNetCore: 'No operations defined in spec!' problem after update of 'Microsoft.AspNetCore.Mvc.ApiExplorer' package to 2.2.0 - asp.net-core

Question

we have .net core 2.1 mvc webapi project which uses Swagger.
we use following packages:
<PackageReference Include="Swashbuckle.AspNetCore" Version="3.0.0" />
<PackageReference Include="Swashbuckle.AspNetCore.Annotations" Version="3.0.0" />
<PackageReference Include="Swashbuckle.AspNetCore.Filters" Version="4.3.0" />
<PackageReference Include="Microsoft.AspNetCore.Mvc.ApiExplorer" Version="2.1.2" />
<PackageReference Include="Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer" Version="2.2.0" />
<PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="2.1.1" />
swashbuckle is configured in following way:
services.AddMvcCore().AddVersionedApiExplorer();
services.AddApiVersioning();
services.AddSwaggerGen();
everything woks in such setup (/swagger/v1/swagger.json has all operations and definitions and UI is rendered properly -> having all controllers and actions, etc)
we are trying to migrate our .net core project from 2.1 to 2.2 .net core.
In order to do that (without warnings) we need upgrade Microsoft.AspNetCore.Mvc.ApiExplorer nuget from 2.1.2 to 2.2.0.
After this nuget update swagger.json (/swagger/v1/swagger.json) doesn't contain any "paths": {} and "definitions": {} and this results in swagger UI showing no controllers/actions (it renders: No operations defined in spec!
after upgrade package these package versions is updated:
<PackageReference Include="Microsoft.AspNetCore.Mvc.ApiExplorer" Version="2.2.0" /> //was 2.1.2
<PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="2.2.0" /> //was 2.1.1
I've tried to upgrade swashbuckle version to v4.0.0 but it did not resolved the issue.
what im missing which packages needs to be updated also so swagger.json would be generated properly when using Microsoft.AspNetCore.Mvc.ApiExplorer 2.2.0 package ?
or i'm missing something else ?

Answer 1

Just had the same issue, thought I'd share my solution too. Version 6.0.4.
I had to add the [ApiController] attribute to my controllers. Swagger must be using that for discovery.

Answer 2

change public methods in controllers to [NoAction] Attribute.
Also, Change all actions with explicit action Methods to [HttpGet("api/get-customer")], [HttpPost("api/save-customer")] instead of [Route("api/get-customer")].

Answer 3

I found how to fix this issue (also posted to: https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/1166#issuecomment-497800414)
In short: i needed to change my HOST project SDK: from 'Microsoft.NET.Sdk' to 'Microsoft.NET.Sdk.Web'.
i did not find explicitly is it should be like that for sure (but default Microsoft template uses this SDK in .net core 2.2)
so it would be great if someone could explain why .Web SDK needs to be used after migration from .net core 2.1 to 2.2

Answer 4

Verify the decorator
[ApiController]
[Route("[controller]")]

Answer 5

Calling both app.UseSwagger(); and app.UseSwaggerUI(c => { c.SwaggerEndpoint("/swagger/v1/swagger.json", "Sonic App"); }); can cause this error as well.

Answer 6

Just add [ApiController] attribute to controllers. It works for Swashbuckle.AspNetCore 6.4.0