JSON Restful服务。无法从System.String转换或转换为System.Collections.Generic.List

Question

我在序列化和反序列化json时遇到了问题。我一直在寻找答案，虽然我在其他地方也看到了同样的问题，但没有一个答案对我有帮助。我在使用newtonsoft或javascriptserializer时也遇到了同样的问题。

我在rest服务中的web方法

[OperationContract(Name="Customers")]
[WebInvoke(Method = "GET",
        ResponseFormat = WebMessageFormat.Json,
        UriTemplate = "json/Customer/Read/{CustomerID}/{CustomerCode}/{ParentCustomerID}/{CustomerName}")]
String JSONReadCustomers(String CustomerID, String CustomerCode, String ParentCustomerID, String CustomerName);

这个类

public class Customer
{
    public Int32 CustomerID { get; set; }
    public String CustomerCode { get; set; }
    public String CustomerName { get; set; }
    public Customer(DataRow DR)
    {
        CustomerID = Convert.ToInt32(DR["CustomerID"]);
        CustomerCode = (DR["CustomerCode"] != null) ? DR["CustomerCode"].ToString() : "";
        CustomerName = (DR["CustomerName"] != null) ? DR["CustomerName"].ToString() : "";
    }
}

实际执行序列化的位

private String GetJSON(DataTable DT)
{
    try
    {
        List<Customer> customers = new List<Customer>();
        foreach (DataRow DR in DT.Rows)
        {
            customers.Add(new Customer(DR));
        }

        return JsonConvert.SerializeObject(customers);
    }
    catch
    {
        throw;
    }
}

到目前为止，一切似乎都很好。服务编译并运行正常。当我在浏览器中测试它时，我得到了以下结果

"[{\"CustomerID\":1,\"CustomerCode\":\"AMT-1\",\"CustomerName\":\".AMTDisp\"},{\"CustomerID\":2,\"CustomerCode\":\"COM-2\",\"CustomerName\":\".ComexDisp,_\"}]"

我使用了一个VB测试工具，调用rest服务并反序列化返回的json

班级

Public Class Customer
    Public CustomerID As Int32
    Public CustomerCode As String
    Public CustomerName As String
End Class

该方法

Private Function DeserializeJSON() As List(Of Customer)

    Dim request As WebRequest = WebRequest.Create(GetCustomerURL())
    request.Credentials = CredentialCache.DefaultCredentials
    Dim response As WebResponse = request.GetResponse()
    Dim dataStream As Stream = response.GetResponseStream()

    Dim reader As New StreamReader(dataStream)
    Dim responseJSON As String = reader.ReadToEnd()

    Dim customers As List(Of Customer) = JsonConvert.DeserializeObject(Of List(Of Customer))(responseJSON)
    Return customers

End Function

错误

{"Could not cast or convert from System.String to System.Collections.Generic.List`1[RESTTestHarness.Customer]."}

我使用了各种不同的方法，比如将bodystyle设置为包装，以及设置一个根对象。似乎什么都不起作用。我总是得到相同的错误。我相信这里的错误真的很简单，但我现在看不到它。

Answer 1

如果您想返回一个通用的json响应，您需要更改您的服务操作契约，以返回消息而不是字符串。

然后，您的服务操作实现应该如下所示：

public System.ServiceModel.Channels.Message CreateJsonResponse()
{
  List<Customer> response = GetCustomers(); 

  string msg = JsonConvert.SerializeObject(response);

  return WebOperationContext.Current.CreateTextResponse(msg, "application/json; charset=utf-8", Encoding.UTF8);
}