无法反序列化当前的 JSON 对象，为什么会出现这个错误？

Question

我正在尝试使用 WebApi 从我的数据库中获取员工列表，使用以下代码：这是我的客户端 MVC 应用程序的代码：

string u = "http://localhost:1411/api/EmployeeAPI";
Uri uri = new Uri(u);

HttpClient httpClient = new HttpClient();

Task<HttpResponseMessage> response = httpClient.GetAsync(uri);

Task.WaitAll(response);

HttpResponseMessage resposta = response.Result;

var msg = resposta.Content.ReadAsStringAsync().Result;

Employee[] employees = JsonConvert.DeserializeObject<Employee[]>(msg);

return View(employees);

这是我的 WebAPI 的代码：

public IEnumerable<Employee> GetEmployees()
{
return db.Employees.AsEnumerable();
}

但是这个错误不断弹出，我不明白为什么：

Cannot deserialize the current JSON object (e.g. {"name":"value"}) 
into type 'DataAccess.Employee[]' because the type requires a 
JSON array (e.g. [1,2,3]) to deserialize correctly. To fix this error either 
change the JSON to a JSON array (e.g. [1,2,3]) or change the deserialized 
type so that it is a normal .NET type (e.g. not a primitive type like integer, 
not a collection type like an array or List) 
that can be deserialized from a JSON object. 
JsonObjectAttribute can also be added to the type to force it to deserialize 
from a JSON object. Path 'Message', line 1, position 11.

我的员工班级：

namespace DataAccess
{
using System;
using System.Collections.Generic;

public partial class Employee
{
    public Employee()
    {
        this.Products = new HashSet<Product>();
    }

    public int EmployeeId { get; set; }
    public string Title { get; set; }
    public string FirstName { get; set; }
    public string MiddleName { get; set; }
    public string LastName { get; set; }
    public byte[] rowguid { get; set; }
    public System.DateTimeOffset ModifiedDate { get; set; }

    public virtual ICollection<Product> Products { get; set; }
 }
}

我的儿子

"{\"Message\":\"An error has occurred.\",\
"ExceptionMessage\":\"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.\",\
"ExceptionType\":\"System.InvalidOperationException\",\
"StackTrace\":null,\
"InnerException\":{\
"Message\":\"An error has occurred.\",\
"ExceptionMessage\":\"Self referencing loop detected with type 'System.Data.Entity.DynamicProxies.ProductSubCategory_9EC9A3706390DE6A3B51F713F0DDAC2162AFB5B3FAB8F8587C9A865333A7729A'. 
Path '[0].Products[0].ProductSubCategory.ProductCategory.ProductSubCategories'.\",\
"ExceptionType\":\"Newtonsoft.Json.JsonSerializationException\",\
"StackTrace\":\" 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value)\r\n 
at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value)\r\n at System.Net.Http.Formatting.JsonMediaTypeFormatter.<>c__DisplayClassd.b__c()\r\n at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token)\"}}"

Answer 1

我认为，如果您查看异常消息，您也许可以深入研究问题。

异常消息表示检测到自引用循环。您能否查看/分享模型 ==> Products[0].ProductSubCategory.ProductCategory.ProductSubCategories'

"ExceptionMessage\":\"Self referencing loop detected with type 'System.Data.Entity.DynamicProxies.ProductSubCategory_9EC9A3706390DE6A3B51F713F0DDAC2162AFB5B3FAB8F8587C9A865333A7729A'. 
Path '[0].Products[0].ProductSubCategory.ProductCategory.ProductSubCategories'.\",\
"ExceptionType\":\"Newtonsoft.Json.JsonSerializationException\",\
"StackTrace\":\" 
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty)