GraphQL .NET Core 中的订阅不会向客户端发送响应

Question

我正在 Asp Net Core 3.1 中构建 GraphQL API。我正在尝试添加一个 subscription，它会在添加时向订阅者发送一个新实体。 当我从 /ui/playground 执行订阅时，与服务器的握手似乎成功了：

GraphQL http 请求 websocket：

当我执行添加评论的突变时，它成功并在数据库上创建了一条记录，但上面的屏幕保持原样，没有更新，没有从套接字接收到数据。

这是突变：

Field<ReviewType>(
    "createReview",
    arguments: new QueryArguments(
        new QueryArgument<NonNullGraphType<ReviewInput>> 
        { 
            Name = "reviewInput"
        }
    ),
    resolve: context =>
    {
        var review = context.GetArgument<Review>("reviewInput");
        var rev = reviewService.Add(review);
        return rev;
    }
);

ShopSubscrition.cs

public partial class ShopSubscription : ObjectGraphType
{
    private readonly IReviewService _reviewService;

    public ShopSubscription(IReviewService reviewService)
    {
        _reviewService = reviewService;
        AddField(new EventStreamFieldType
        {
            Name = "reviewAdded",
            Type = typeof(ReviewType),
            Resolver = new FuncFieldResolver<Review>((context) => context.Source as Review),
            Subscriber = new EventStreamResolver<Review>((context) => _reviewService.ReviewAdded())
        });
    }
}

ReviewService.cs

public class ReviewService : IReviewService
{
    private readonly IReviewRepository _reviewRepository;
    private readonly ISubject<Review> _sub = new ReplaySubject<Review>(1);

    public ReviewService(IReviewRepository reviewRepository)
    {
        _reviewRepository = reviewRepository;
    }

    public Review Add(Review review)
    {
        var addedEntity = _reviewRepository.Add(review);
        _sub.OnNext(review);
        return review;
    }

    public IObservable<Review> ReviewAdded()
    {
        return _sub.AsObservable();
    }
}

我也 post Startup.cs，也许它可以帮助。

Startup.cs

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

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

        services.AddDbContext<ShopDbContext>(opt =>
            opt.UseSqlServer(Configuration.GetConnectionString("Default")));

        services.AddScoped<ISupplierRepository, SupplierRepository>();
        services.AddScoped<IProductRepository, ProductRepository>();
        services.AddScoped<IReviewRepository, ReviewRepository>();

        services.AddScoped<IReviewService, ReviewService>();

        services.AddSingleton<IDataLoaderContextAccessor, DataLoaderContextAccessor>();
        services.AddSingleton<DataLoaderDocumentListener>();

        services.AddScoped<ShopSchema>();
        services.AddGraphQL(options =>
        {
            options.EnableMetrics = false;
        })
            .AddWebSockets()
            .AddSystemTextJson()
            .AddGraphTypes(typeof(ShopSchema), ServiceLifetime.Scoped).AddDataLoader();

        services.AddControllers()
            .AddNewtonsoftJson(o => o.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore);
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ShopDbContext dbContext)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseCors("Cors");
        app.UseHttpsRedirection();
        app.UseRouting();
        app.UseAuthorization();
        app.UseWebSockets();
        app.UseGraphQLWebSockets<ShopSchema>("/graphql");

        app.UseGraphQL<ShopSchema>();
        app.UseGraphQLPlayground(options: new GraphQLPlaygroundOptions { GraphQLEndPoint ="/graphql", SchemaPollingEnabled = false });

        
        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
        dbContext.SeedData();
    }
}

在此先感谢您的帮助。

Answer 1

经过更深入的调查，我发现了问题所在。我 post 解决方案，也许可以帮助某人。

问题与依赖注入有关：包含订阅“通知逻辑”（在我的例子中 ReviewService.cs）的 class 必须注册为 Singleton 而不是 Scoped。这引起了一种连锁反应，使存储库 classes 被注册为 Transient。 这是工作代码：

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddCors(options => options.AddPolicy("Cors",
            builder =>
            {
                builder.AllowAnyOrigin()
                .AllowAnyMethod()
                .AllowAnyHeader();
            }));

        services.AddDbContext<ShopDbContext>(opt =>
            opt.UseSqlServer(Configuration.GetConnectionString("Default")));

        services.AddTransient<ISupplierRepository, SupplierRepository>();
        services.AddTransient<IProductRepository, ProductRepository>();
        services.AddTransient<IReviewRepository, ReviewRepository>();

        services.AddSingleton<IReviewService, ReviewService>();

        services.AddSingleton<IDataLoaderContextAccessor, DataLoaderContextAccessor>();
        services.AddSingleton<DataLoaderDocumentListener>();

        services.AddScoped<ShopSchema>();
        services.AddGraphQL(options =>
        {
            options.EnableMetrics = false;  // info sulla richiesta (ms, campi richiesti, ecc)
        })
            .AddWebSockets()
            .AddSystemTextJson()
            .AddGraphTypes(typeof(ShopSchema), ServiceLifetime.Scoped).AddDataLoader();

        services.AddControllers()
            .AddNewtonsoftJson(o => o.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore);
    }