ASP.NET Core API POST parameter is always null

Question

I have read the following:

• Asp.net Core Post parameter is always null
• asp.net webapi 2 post parameter is always null
• web-api POST body object

Answer 1

My particular issue was that the model binding was silently failing for a JSON model. (It was always null).

As I had the exact JSON being posted, I was able to debug it locally by running the web-service locally, and posting to my controller via cURL (can use POSTMAN).

Using the below code, I was able to see the exact exception occurring during serialization.

    [HttpPost]
    public IActionResult MyAction([FromBody] dynamic request)
    {            
        if (request != null)
        {
            try
            {
                var objAttempt =
                    JsonConvert.DeserializeObject<MyModel>(
                        JsonConvert.SerializeObject(request));
            }
            catch (Exception exception)
            {
                Console.WriteLine(exception);
                throw;
            }
        }

Answer 2

ridiculously, in dot net core you cannot use just "frombody string parameter". you should make a model class for just one string parameter.

public async Task<IActionResult> GetRankings([FromBody] string cookie)

=>

//1. make a model. MyCookie.cs
class MyCookie{
   public string Cookie { get; set; }
}
//2. edit your parameter
public async Task<IActionResult> GetRankings([FromBody] MyCookie cookie)

Answer 3

I needed to post string data by .Net Desktop Client to .NET Core host. I was getting unsupported media error. I have followed Shaun Luttin's answer and worked fine. The I found something easier to get just string data as folows in case someone else finds useful:

[HttpPost]
[Route("Request/Echo")]
public async Task<string> Echo()
{
    using (var Reader = new StreamReader(Request.Body, Encoding.UTF8))
    {
        return await Reader.ReadToEndAsync();
    }
}

This post is very useful.

Answer 4

I struggled with this for far to long and finally, after looking at what a DevExpress control was doing for "PUT"ting to a Razor Page, I discovered this nugget:

JavaScript

$.ajax({
        type: "PUT",
        url: "/GoalGrid?handler=Single",
        dataType: "json",
        contentType: "application/x-www-form-urlencoded; charset=UTF-8",
        data: {values: single }
    })

GoalGrid.cshtml.cs

public JsonResult OnPutSingle(string values)
{ 
     // Do stuff with 'values' here 
}

The trick is to use the "application/x-www-form-urlencoded; charset=UTF-8" as your contentType for the request. This way you don't need to create a class for a single string value. And things work as expected.

Answer 5

For me, just adding [FromBody] to the parameters list solved the problem.

May this save someone's time.

Answer 6

You simply need to put the body in quotes such that it represents a string. You also need to leave the request type as application/json. That way the media type formatter will figure it out:

"=sec_session_id=[redacted]; _ga=[redacted]; AWSELB=[redacted]"

Should do the trick.