Csharp 来自 c# 后端 System.NotSupportedException 的 GET 方法错误

发布于08月31日

我是C#的超级新手，我不知道自己在做什么.我得到了一个任务，将C#后端与本地SQL服务器一起使用，并将数据获取/发布到数据库中.

我一直在学习教程，直到我try 从SQL表中获取数据时遇到问题:

System.NotSupportdException:不支持序列化和反序列化""System.Type""实例.路径:$.Columns.DataType. -&gt；System.NotSupportdException:不支持序列化和反序列化""System.Type""实例." 在System.Text.Json.Serialization.Converters.UnsupportedTypeConverter1.Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options) at System.Text.Json.Serialization.JsonConverter1.TryWrite(Utf8JsonWriter编写器、T&A；值、JsonSerializerOptions、WriteStack&A；状态) 在System.Text.Json.Serialization.Metadata.JsonPropertyInfo1.GetMemberAndWriteJson(Object obj, WriteStack& state, Utf8JsonWriter writer) at System.Text.Json.Serialization.Converters.ObjectDefaultConverter1.OnTryWrite(Utf8JsonWriter编写器、T值、JsonSerializerOptions、WriteStack&A；状态) 在System.Text.Json.Serialization.JsonConverter1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.JsonConverter1.TryWriteAsObject(Utf8JsonWriter编写器、对象值、JsonSerializerOptions、WriteStack&A；状态) 在System.Text.Json.Serialization.JsonConverter1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.Converters.IEnumerableConverter1.OnWriteResume(Utf8JsonWriter编写器、T集合值、JsonSerializerOptions、WriteStack&A；状态) 在System.Text.Json.Serialization.JsonCollectionConverter2.OnTryWrite(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.JsonConverter1.TryWrite(Utf8JsonWriter编写器、T&A；值、JsonSerializerOptions、WriteStack&A；状态) 在System.Text.Json.Serialization.Metadata.JsonPropertyInfo1.GetMemberAndWriteJson(Object obj, WriteStack& state, Utf8JsonWriter writer) at System.Text.Json.Serialization.Converters.ObjectDefaultConverter1.OnTryWrite(Utf8JsonWriter编写器、T值、JsonSerializerOptions、WriteStack&A；状态) 在System.Text.Json.Serialization.JsonConverter1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.JsonConverter1.WriteCore(Utf8JsonWriter编写器、T&A；值、JsonSerializerOptions、WriteStack&A；状态) -内部异常堆栈跟踪结束在System.Text.Json.ThrowHelper.ThrowNotSupportedException(WriteStack&amp；状态下，不支持异常(Ex) 在System.Text.Json.Serialization.JsonConverter1.WriteCore(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.Serialization.JsonConverter1.WriteCoreAsObject(Utf8JsonWriter编写器、对象值、JsonSerializerOptions、WriteStack&A；状态) 在System.Text.Json.JsonSerializer.WriteCore[TValue](JsonConverter jsonConverter、Utf8JsonWriter、TValue&amp；Value、JsonSerializerOptions、WriteStack&amp；状态) At System.Text.Json.JsonSerializer.WriteStreamAsync[TValue](Stream utf8Json，TValue Value，JsonTypeInfo jsonTypeInfo，CancerationToken ancellationToken) At System.Text.Json.JsonSerializer.WriteStreamAsync[TValue](Stream utf8Json，TValue Value，JsonTypeInfo jsonTypeInfo，CancerationToken ancellationToken) At System.Text.Json.JsonSerializer.WriteStreamAsync[TValue](Stream utf8Json，TValue Value，JsonTypeInfo jsonTypeInfo，CancerationToken ancellationToken) 在Microsoft.AspNetCore.Mvc.Infrastructure.SystemTextJsonResultExecutor.ExecuteAsync(ActionContext上下文中，JsonResult结果) At Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|30_0[TFilter，TFilterAsync](资源调用器调用器，任务最后任务，下一个状态，作用域，对象状态，布尔值已完成) 在Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed环境中) 在Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter，T筛选器异步](状态&A；下一个、作用域&A；范围、对象&A；状态、布尔值&A；已完成) 在Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters() -来自前一位置的堆栈结束跟踪在Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|20_0(ResourceInvoker调用方，任务最后任务、状态下一个、作用域、对象状态、布尔值isComplete) 在Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0(ResourceInvoker调用方，任务任务，IDisposable作用域) 在Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0(ResourceInvoker调用方，任务任务，IDisposable作用域) 在Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0(Endpoint终结点，任务请求任务、日志(log)记录器) 在Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext环境中) 在Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext HttpContext上) 在Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext http上下文中，iswaggerProvider swaggerProvider) 在Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext环境中)

国家元首和政府首脑

接受度:/

连接:保持连接

Host: localhost:5291

用户代理:PostmanRuntime/7.29.2

Accept-编码:GZIP、DEFEATE、br

postman -令牌:ad516da9-02bb-424f-8979-64365d710b2c

Error message个

This is my controller个

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Data;
using System.Data.SqlClient;
using Microsoft.Extensions.Configuration;
using webApi.Models;
using Microsoft.AspNetCore.Hosting;
using System.IO;

namespace webApi.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class ContactController : ControllerBase
    {
        private readonly IConfiguration _configuration;
        private readonly IWebHostEnvironment _env;
        public ContactController(IConfiguration configuration, IWebHostEnvironment env)
        {
            _configuration = configuration;
            _env = env;
        }

        [HttpGet]
        public JsonResult Get()
        {
            string query = @"select ContactName from dbo.Contact";

            DataTable table = new DataTable();
            string sqlDataSource = _configuration.GetConnectionString("ContactAppCon");
            SqlDataReader myReader;
            using (SqlConnection myCon = new SqlConnection(sqlDataSource))
            {
                myCon.Open();
                using (SqlCommand myCommand = new SqlCommand(query, myCon))
                {
                    myReader = myCommand.ExecuteReader();
                    table.Load(myReader);
                    myReader.Close();
                    myCon.Close();
                }
            }

            return new JsonResult(table);
        }
    }
}

This is model个

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace webApi.Models
{
    public class Contact
    {
        public int ContactID { get; set; }

        public string ContactName { get; set; }

        public string ContactEmail { get; set; }

        public string ContactSubject { get; set; }

        public string ContactMessage { get; set; }


   
    }
}

This is startup.cs个

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Newtonsoft.Json.Serialization;
using Microsoft.Extensions.FileProviders;
using System.IO;

namespace WebApplication1
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            //Enable CORS
            services.AddCors(c =>
            {
                c.AddPolicy("AllowOrigin", options => options.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader());
            });


            //JSON Serializer
            _ = services.AddControllersWithViews().AddNewtonsoftJson(options =>
            options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore)
                .AddNewtonsoftJson(options => options.SerializerSettings.ContractResolver
                = new DefaultContractResolver());

            services.AddControllers();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            //Enable CORS
            app.UseCors(options => options.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader());

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseRouting();

            app.UseAuthorization();

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

            app.UseStaticFiles(new StaticFileOptions
            {
                FileProvider = new PhysicalFileProvider(
                   Path.Combine(Directory.GetCurrentDirectory(), "Photos")),
                RequestPath = "/Photos"
            });
        }
    }
}

Csharp 来自 c# 后端 System.NotSupportedException 的 GET 方法错误

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