How to handle JSON data in POST request in C# (.NET Core 3.1)

Question

Previously (In .Net Core 2.1) I successfully handled JSON data with below method

[HttpPost]
[Route("sendJsonData")]
public JObject saveTemplate(JObject jsonString)
{

        string templateName = (string)jsonString.SelectToken("templateName");
        string filePathAndName = "D:\\" + "templates\\" + templateName + ".txt";

        using (StreamWriter file = File.CreateText(@filePathAndName))
        {
            JsonSerializer serializer = new JsonSerializer();
            serializer.Serialize(file, jsonString);
        }

    return jsonString;
}

But when I created the same method with .Net Core 3.1. It is not working showing some error with JObject. I am getting that JSON from below code

onSubmit() {
this.http.post("https://localhost:44350/ReportAPI/sendJsonData", this.surveyForm.value)
            .subscribe(
                data => console.log("success!", data),
                error => console.error("couldn't post because", error)
            );
}

Below is the error (Response from Postman)

{
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "|6e209814-4dd7396cc2dfa182.",
    "errors": {
        "$": [
            "The JSON value could not be converted to System.Collections.Generic.IEnumerable`1[Newtonsoft.Json.Linq.JToken]. Path: $ | LineNumber: 0 | BytePositionInLine: 14."
        ]
    }
}

JSON

{  
   "templateName":"BFS Survey",
   "surveyQuestions":[  
      {  
         "questionTitle":"Name",
         "questionType":"Text",
         "questionGroup":{  

         }
      },
      {  
         "questionTitle":"Age",
         "questionType":"Number",
         "questionGroup":{  

         }
      },
      {  
         "questionTitle":"Gender",
         "questionType":"Single choice",
         "questionGroup":{  
            "options":[  
               {  
                  "optionText":"Male"
               },
               {  
                  "optionText":"Female"
               },
               {  
                  "optionText":"Other"
               }
            ],
            "showRemarksBox":false
         }
      },
      {  
         "questionTitle":"Skills",
         "questionType":"Multi choice",
         "questionGroup":{  
            "options":[  
               {  
                  "optionText":"Java"
               },
               {  
                  "optionText":"Angular"
               },
               {  
                  "optionText":"Python"
               },
               {  
                  "optionText":"R"
               }
            ],
            "showRemarksBox":false
         }
      }
   ]
}

Code perfectly worked using .Net Core 2.1 but not working with 3.1. Please suggest me how resolve this issue.

Answer 1

In order to migrate from ASP.NET Core 2.x to 3.0, refer to this link:

• Add a package reference to Microsoft.AspNetCore.Mvc.NewtonsoftJson
• Add in Startup.cs, in method ConfigureServices: services.AddMvc().AddNewtonsoftJson();