asp.net-core - JsonResult(object) 导致“不支持集合类型'Newtonsoft.Json.Linq.JToken'。”

Question

我将现有的 ASP.NET Core 2.2 项目升级到 3.0。我有一个返回 JSON 的方法，该方法在 2.2 中有效，但在 3.0 中，它会导致“不支持集合类型‘Newtonsoft.Json.Linq.JToken’。” 在返回。

[HttpGet()]
public async Task<JsonResult> Get()
{
    var res = some class object in a third-party library;
    return new JsonResult(res);
}

我搜索了谷歌，发现微软已经将 Newtonsoft Json 替换为System.Text.Json，但我没有明确使用 Newtonsoft Json。在项目的“框架”中，我可以看到 Newtonsoft Json，我删除了它和using Newtonsoft.Json.Linq语句，但结果是一样的。如何不使用 Newtonsoft Json？

错误信息是：

System.NotSupportedException: The collection type 'Newtonsoft.Json.Linq.JToken' is not supported.
   at System.Text.Json.JsonClassInfo.GetElementType(Type propertyType, Type parentType, MemberInfo memberInfo, JsonSerializerOptions options)
   at System.Text.Json.JsonClassInfo.CreateProperty(Type declaredPropertyType, Type runtimePropertyType, Type implementedPropertyType, PropertyInfo propertyInfo, Type parentClassType, JsonConverter converter, JsonSerializerOptions options)
   at System.Text.Json.JsonClassInfo.AddProperty(Type propertyType, PropertyInfo propertyInfo, Type classType, JsonSerializerOptions options)
   at System.Text.Json.JsonClassInfo.AddPolicyProperty(Type propertyType, JsonSerializerOptions options)
   at System.Text.Json.JsonClassInfo..ctor(Type type, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializerOptions.GetOrAddClass(Type classType)
   at System.Text.Json.JsonPropertyInfo.get_ElementClassInfo()
   at System.Text.Json.JsonSerializer.HandleObject(JsonPropertyInfo jsonPropertyInfo, JsonSerializerOptions options, Utf8JsonWriter writer, WriteStack& state)
   at System.Text.Json.JsonSerializer.WriteObject(JsonSerializerOptions options, Utf8JsonWriter writer, WriteStack& state)
   at System.Text.Json.JsonSerializer.Write(Utf8JsonWriter writer, Int32 originalWriterDepth, Int32 flushThreshold, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.JsonSerializer.WriteAsyncCore(Stream utf8Json, Object value, Type inputType, JsonSerializerOptions options, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Mvc.Infrastructure.SystemTextJsonResultExecutor.ExecuteAsync(ActionContext context, JsonResult result)
   at Microsoft.AspNetCore.Mvc.Infrastructure.SystemTextJsonResultExecutor.ExecuteAsync(ActionContext context, JsonResult result)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeResultAsync>g__Logged|21_0(ResourceInvoker invoker, IActionResult result)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

---

PS：我已经尝试过其他类型，并得到了一些类似的集合类型的异常消息。有了这个，我搜索了 Google 并在 .NET Core 的 GitHub 上找到了这个未解决的问题。目前似乎System.Text.JSon不完全支持集合类型，解决方法是使用旧的 Newtonsoft Json。

标签： asp.net-coreasp.net-core-3.0

Answer 1

从 ASP.NET Core 2.2 迁移到 3.0

• 添加对 Microsoft.AspNetCore.Mvc.NewtonsoftJson 的包引用

• 更新 Startup.ConfigureServices 以调用 AddNewtonsoftJson： services.AddMvc().AddNewtonsoftJson();