c# - 可选参数导致 Swashbuckle.AspNetCore 中出现空异常

Question

我有一个asp.net core 2.0带有可选（和可为空）参数的 api 控制器操作。Swashbuckle.AspNetCore 1.0.0当方法签名中存在此参数时，Swagger 文档的生成失败，但如果我将其从签名中删除，则会成功。看来可选参数是错误的原因，但我不知道为什么......

我正在使用与 aspnet-api-versioning 的 Swashbuckle 集成： https ://github.com/Microsoft/aspnet-api-versioning/wiki/Swashbuckle-Integration

控制器动作：

[HttpGet("{id}")]
public IActionResult GetPerson(int id, [FromQuery] bool? includeContactInfo = null)
{
    var includeInfo = (includeContactInfo.HasValue && includeContactInfo.Value == true);
    var person = _repo.GetPerson(id, includeInfo);
    if (person == null)
    {
        return NotFound();
    }

    if (includeInfo)
    {
        // using AutoMapper to map between entity and dto
        var personFullDto = Mapper.Map<PersonFullDto>(person);
        return Ok(personFullDto);
    }

    var personBasicDto = Mapper.Map<PersonBasicDto>(person);
    return Ok(personBasicDto);
}

以下是我的ConfigureServices和Configure方法startup.cs：

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvcCore().AddVersionedApiExplorer(o => o.GroupNameFormat = "'v'VVV");
    services.AddMvc();

    services.AddApiVersioning(o =>
    {
        o.ReportApiVersions = true;
        o.DefaultApiVersion = new Microsoft.AspNetCore.Mvc.ApiVersion(1, 0);
    });

    services.AddSwaggerGen(options =>
    {
        var provider = services.BuildServiceProvider().GetRequiredService<IApiVersionDescriptionProvider>();
        foreach (var description in provider.ApiVersionDescriptions)
        {
            options.SwaggerDoc(description.GroupName, CreateInfoForApiVersion(description));
        }
        options.OperationFilter<SwaggerDefaultValues>();
        options.IncludeXmlComments(XmlCommentsFilePath);
    });

    var connectString = Startup.Configuration["connectionStrings:ContactsAppDb"];
    services.AddDbContext<ContactsDbContext>(o => o.UseSqlServer(connectString));
    services.AddScoped<IContactsRepository, ContactsRepository>();
}


public void Configure(IApplicationBuilder app, IHostingEnvironment env, IApiVersionDescriptionProvider provider)
{
    if (env.IsEnvironment("PROD"))
    {
        app.UseExceptionHandler();
    }
    else
    {
        app.UseDeveloperExceptionPage();
    }

    app.UseStatusCodePages();

    AutoMapper.Mapper.Initialize(cfg =>
    {
        cfg.CreateMap<Entities.Person, Models.PersonBasicDto>();
        cfg.CreateMap<Entities.Person, Models.PersonFullDto>();
        cfg.CreateMap<Entities.ContactInfo, Models.ContactInfoDto>();
    });

    app.UseMvc();

    app.UseSwagger();
    app.UseSwaggerUI(options =>
    {
        // build a swagger endpoint for each discovered API version
        foreach (var description in provider.ApiVersionDescriptions)
        {
            options.SwaggerEndpoint($"/swagger/{description.GroupName}/swagger.json", description.GroupName.ToUpperInvariant());
        }
    });
}

我也在使用来自 https://github.com/Microsoft/aspnet-api-versioning/wiki/Swashbuckle-Integration#aspnet-core的 SwaggerDefaultValues.cs 类

public class SwaggerDefaultValues : IOperationFilter
{
    public void Apply( Operation operation, OperationFilterContext context )
    {
        foreach ( var parameter in operation.Parameters.OfType<NonBodyParameter>() )
        {
            var description = context.ApiDescription
                                     .ParameterDescriptions
                                     .First( p => p.Name == parameter.Name );

            if ( parameter.Description == null )
            {
                parameter.Description = description.ModelMetadata.Description;
            }

            if ( parameter.Default == null )
            {
                parameter.Default = description.RouteInfo.DefaultValue;
            }

            parameter.Required |= !description.RouteInfo.IsOptional;
        }
    }
}

当我导航到 Swagger URL 时，以下代码行失败（在 SwaggerDefaultValues.cs 类中）：

parameter.Default = description.RouteInfo.DefaultValue;

当我检查description对象的includeContactInfo可选/查询参数时，它description.RouteInfo是空的。

错误信息：

Object reference not set to an instance of an object.

堆栈跟踪：

at ContactsApp.Services.SwaggerDefaultValues.Apply(Operation operation, OperationFilterContext context) in C:\Users\me\Documents\Visual Studio 2017\Projects\ContactsApp\ContactsApp\Services\SwaggerDefaultValues.cs:line 37
at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.CreateOperation(ApiDescription apiDescription, ISchemaRegistry schemaRegistry)
at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.CreatePathItem(IEnumerable`1 apiDescriptions, ISchemaRegistry schemaRegistry)
at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwagger(String documentName, String host, String basePath, String[] schemes)
at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.<Invoke>d__6.MoveNext()

Answer 1

使用空条件运算符：

parameter.Default = description.RouteInfo?.DefaultValue;