json string on POST to MVC action method using AJAX is null

Question

I am getting a hard time to find out why the string sent via AJAX request is null. Console.WriteLine(data) shows empty. Status is 200 OK. If I add some code to parse the string received, I get an error stating that JObject.Parse cannot be null. I don't know what am I missing. The javascript code is ok. The action method also seems ok, but my knowledge on Asp.Net Core and MVC is very scarce, so I am not sure. Can someone please point out what am I missing?

The javascript code:


    let obj = {email: email_address.value};
    let objStringified = JSON.stringify(obj);
    $.ajax({
       type: 'POST',
       contentType: 'application/json; charset=UTF-8',
       data: objStringified,
       url: '@Url.Action("ReturnCheckAccountDuplication")',
       dataType: 'text',
       success: function(data) {
          console.log(data);
       },
       error: function(error) {
          console.log("Keep trying", error);
       }
    });

C# code:

[HttpPost]
public ActionResult ReturnCheckAccountDuplication([FromBody] string data)
{
   Console.WriteLine(data);
   JObject jObject = JObject.Parse(data);
   string email = (string)jObject["email"];
   bool emailExists = CheckAccountDuplication.Get(email);
   string returnResult = emailExists.ToString();
   return Content(returnResult);
}

The solution on the controller side is

public class AccountCheckModel
{
   public string Email { get; set; }
}

[HttpPost]
public ActionResult ReturnCheckAccountDuplication([FromBody] AccountCheckModel data)
{
   string result = CheckAccountDuplication.Get(data.Email).ToString();
   return Content(result);
}

Thanks to all the members who commented on my problem, especially John Glenn who provided a solution. I had been trying for several days but without success. My knowledge of Asp.Net Core is very poor indeed. Thank you very much.

Does this answer your question? jQuery posts null instead of JSON to ASP.NET Web API — Matthieu Riegler
– Matthieu Riegler, Commented Jan 23, 2022 at 3:02
Hello. It didn't worked for me. I tested the solution described and still got an error. System.ArgumentNullException: Value cannot be null. (Parameter 's') at Newtonsoft.Json.Linq.JObject.Parse(String json, JsonLoadSettings settings) — Luis Rito Filipe
– Luis Rito Filipe, Commented Jan 23, 2022 at 23:38

John Glenn · Accepted Answer · 2022-01-23 06:05:29Z

1

The easiest solution is to create a model representing the JSON data that your controller will receive. For example, create a class like so:

public class AccountCheckModel
{
    public string email { get; set }
}

Then, use it as the parameter for your controller method:

public ActionResult ReturnCheckAccountDuplication([FromBody] AccountCheckModel data)

This is the preferred way to access the request body. To get the request body as a string, you have to jump through some serious hoops.

answered Jan 23, 2022 at 6:05

John Glenn

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1 Comment

Luis Rito Filipe Over a year ago

Great! It works. I changed the controller code and is now as below: public class AccountCheckModel { public string email { get; set; } } [HttpPost] public ActionResult ReturnCheckAccountDuplication([FromBody] AccountCheckModel data){ string email = data.email; bool emailExists = CheckAccountDuplication.Get(email); string result = emailExists.ToString(); return Content(result); }

Rahul Sharma · Accepted Answer · 2022-01-23 07:02:31Z

1

An alternative way to send your data via AJAX to your Controller:

var json = {
       email: email_address.value
};

$.ajax({
   type: 'POST',
   data: {'json': JSON.stringify(json)},
   url: '@Url.Action("ReturnCheckAccountDuplication")',
   dataType: 'json',
   success: function(data) {
      console.log(data);
   },
   error: function(error) {
      console.log("Keep trying", error);
   }
});

And your Controller:

[HttpPost]
public ActionResult ReturnCheckAccountDuplication(string json)
{
   Console.WriteLine(json);
   JObject jObject = JObject.Parse(json);
   string email = (string)jObject["email"];
   bool emailExists = CheckAccountDuplication.Get(email);
   string returnResult = emailExists.ToString();
   return Content(returnResult);
}

edited Jan 23, 2022 at 7:02

answered Jan 23, 2022 at 6:57

Rahul Sharma

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6 Comments

Luis Rito Filipe Over a year ago

I tried your suggestion with just a small change (in dataType, I declared text instead of json). But is not working. The string json is still null in the controller.

Rahul Sharma Over a year ago

@LuisRitoFilipe Well isn't it obvious from the line data: {'json': JSON.stringify(json)},, that you are sending the data as JSON so why would you even change the dataType to text?

Rahul Sharma Over a year ago

@LuisRitoFilipe If you did not change the dataType to text, this would have worked as expected and you would not have to go through the pain of creating models for one field.

Luis Rito Filipe Over a year ago

Rahul Sharma, I tried dataType : json but it didn't work, then I tried dataType : text and it didn't work either. But I changed dataType to text because I expect from server a simple string and not a string in JSON format. But even so, this is not a reason for the controller to recognise the data sent as null. Thank you very much for your support.

Luis Rito Filipe Over a year ago

Rahul Sharma, sure, if I want to return json from server (in case of more complex data), the dataType must be json. But in my specific case I just need a simple string (True/False). Kind regards.

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