How to set up Swashbuckle vs Microsoft.AspNetCore.Mvc.Versioning

Instead of tweaking the OpenAPI document, you can use the library provided by Microsoft that adds versions to the API Explorer. That way the versions are provided before Swashbuckle (or another toolchain) needs it and allows you to avoid custom code.

Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer

I was able to get versions configured correctly after adding the package and this block of code.

services.AddVersionedApiExplorer(
    options =>
    {
    // add the versioned api explorer, which also adds IApiVersionDescriptionProvider service
    // note: the specified format code will format the version as "'v'major[.minor][-status]"
    options.GroupNameFormat = "'v'VVV";

    // note: this option is only necessary when versioning by url segment. the SubstitutionFormat
    // can also be used to control the format of the API version in route templates
    options.SubstituteApiVersionInUrl = true;
    }
);

If working with .Net Core 3, Basically I have taken @Alezis's solution and updated it to work with .Net core 3:

public void ConfigureServices(IServiceCollection services)
    {
     ....
        services.AddSwaggerGen(options =>
        {
            options.SwaggerDoc("v1", new OpenApiInfo() { Title = "My API", Version = "v1" });
            options.OperationFilter<RemoveVersionFromParameter>();

            options.DocumentFilter<ReplaceVersionWithExactValueInPath>();

        });
      ...
    }

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    ...
    app.UseSwagger();
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
    });
   ...
}

public class RemoveVersionFromParameter : IOperationFilter
{
    public void Apply(OpenApiOperation operation, OperationFilterContext context)
    {
        var versionParameter = operation.Parameters.Single(p => p.Name == "version");
        operation.Parameters.Remove(versionParameter);
    }
}

public class ReplaceVersionWithExactValueInPath : IDocumentFilter
{
    public void Apply(OpenApiDocument swaggerDoc, DocumentFilterContext context)
    {
        var paths = new OpenApiPaths();
        foreach (var path in swaggerDoc.Paths)
        {
            paths.Add(path.Key.Replace("v{version}", swaggerDoc.Info.Version), path.Value);
        }
        swaggerDoc.Paths = paths;
    }
}

At the moment Swashbuckle and Microsoft.AspNetCore.Mvc.Versioning are friends. It works good. I just created test project in VS2017 and checked how it works.

First include these two nuget packages:

<PackageReference Include="Microsoft.AspNetCore.Mvc.Versioning" Version="1.2.1" />
<PackageReference Include="Swashbuckle.AspNetCore" Version="1.0.0" />

Configure everything in Startup.cs (read my comments):

public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc();


        // Configure versions 
        services.AddApiVersioning(o =>
        {
            o.AssumeDefaultVersionWhenUnspecified = true;
            o.DefaultApiVersion = new ApiVersion(1, 0);
        });

        // Configure swagger
        services.AddSwaggerGen(options =>
        {
            // Specify two versions 
            options.SwaggerDoc("v1", 
                new Info()
                {
                    Version = "v1",
                    Title = "v1 API",
                    Description = "v1 API Description",
                    TermsOfService = "Terms of usage v1"
                });

            options.SwaggerDoc("v2",
                new Info()
                {
                    Version = "v2",
                    Title = "v2 API",
                    Description = "v2 API Description",
                    TermsOfService = "Terms of usage v2"
                });

            // This call remove version from parameter, without it we will have version as parameter 
            // for all endpoints in swagger UI
            options.OperationFilter<RemoveVersionFromParameter>();

            // This make replacement of v{version:apiVersion} to real version of corresponding swagger doc.
            options.DocumentFilter<ReplaceVersionWithExactValueInPath>();

            // This on used to exclude endpoint mapped to not specified in swagger version.
            // In this particular example we exclude 'GET /api/v2/Values/otherget/three' endpoint,
            // because it was mapped to v3 with attribute: MapToApiVersion("3")
            options.DocInclusionPredicate((version, desc) =>
            {
                var versions = desc.ControllerAttributes()
                    .OfType<ApiVersionAttribute>()
                    .SelectMany(attr => attr.Versions);

                var maps = desc.ActionAttributes()
                    .OfType<MapToApiVersionAttribute>()
                    .SelectMany(attr => attr.Versions)
                    .ToArray();

                return versions.Any(v => $"v{v.ToString()}" == version) && (maps.Length == 0 || maps.Any(v => $"v{v.ToString()}" == version));
            });

        });

    }

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole(Configuration.GetSection("Logging"));
        loggerFactory.AddDebug();

        app.UseSwagger();
        app.UseSwaggerUI(c =>
        {
            c.SwaggerEndpoint($"/swagger/v2/swagger.json", $"v2");
            c.SwaggerEndpoint($"/swagger/v1/swagger.json", $"v1");
        });
        app.UseMvc();
    }

There two classes that make the trick:

public class RemoveVersionFromParameter : IOperationFilter
{
    public void Apply(Operation operation, OperationFilterContext context)
    {
        var versionParameter = operation.Parameters.Single(p => p.Name == "version");
        operation.Parameters.Remove(versionParameter);
    }
}

public class ReplaceVersionWithExactValueInPath : IDocumentFilter
{
    public void Apply(SwaggerDocument swaggerDoc, DocumentFilterContext context)
    {
        swaggerDoc.Paths = swaggerDoc.Paths
            .ToDictionary(
                path => path.Key.Replace("v{version}", swaggerDoc.Info.Version),
                path => path.Value
            );
    }
}

The RemoveVersionFromParameter removes from swagger UI this textbox:

The ReplaceVersionWithExactValueInPath change this:

to this:

Controller class looks now as follows:

[Route("api/v{version:apiVersion}/[controller]")]
[ApiVersion("1")]
[ApiVersion("2")]
public class ValuesController : Controller
{
    // GET api/values
    [HttpGet]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2" };
    }

    // GET api/values/5
    [HttpGet("{id}")]
    public string Get(int id)
    {
        return "value";
    }

    // POST api/values
    [HttpPost]
    public void Post([FromBody]string value)
    {
    }

    // PUT api/values/5
    [HttpPut("{id}")]
    public void Put(int id, [FromBody]string value)
    {
    }

    // DELETE api/values/5
    [HttpDelete("{id}")]
    public void Delete(int id)
    {
    }


    [HttpGet("otherget/one")]
    [MapToApiVersion("2")]
    public IEnumerable<string> Get2()
    {
        return new string[] { "value1", "value2" };
    }

    /// <summary>
    /// THIS ONE WILL BE EXCLUDED FROM SWAGGER Ui, BECAUSE v3 IS NOT SPECIFIED. 'DocInclusionPredicate' MAKES THE
    /// TRICK 
    /// </summary>
    /// <returns></returns>
    [HttpGet("otherget/three")]
    [MapToApiVersion("3")]
    public IEnumerable<string> Get3()
    {
        return new string[] { "value1", "value2" };
    }
}

---

Code: https://gist.github.com/Alezis/bab8b559d0d8800c994d065db03ab53e