c# .net core web api x-www-form-urlencoded parameter is always null

Question

I have this method that looks a bit like this:

/// <summary>
/// Updates the status to paid
/// </summary>
/// <param name="data">The data from world pay</param>
/// <returns></returns>
[HttpPost]
[Consumes("application/x-www-form-urlencoded")]
public IActionResult Residential([FromForm] string data)
{
    if (string.IsNullOrEmpty(data)) return BadRequest("No data was present");

    var model = JsonConvert.DeserializeObject<WorldPayResponseModel>(data);

    // ----- removed from brevity ----- //

    return Ok(true);
}

When I use postman to send some data, it is always null.

Does anyone have any idea why this might be?

Answer 1

Create a model/DTO for the data being posted, .net core should handle the binding ( Model Binding in ASP.NET Core ).

You seem to already have WorldPayResponseModel , so why not bind to that? For example:

public class WorldPayResponseModel
{
    public string CardType { get; set; } 
    public int CardId { get; set; } 
    // other properties
    ...
}

[HttpPost]
[Consumes("application/x-www-form-urlencoded")]
public IActionResult Residential([FromForm] WorldPayResponseModel model)
{
    if (model == null || !ModelState.IsValid) return BadRequest("No data was present");    

    // ----- removed from brevity ----- //

    return Ok(true);
}

You can also add DataAnnotations to the properties, then in the controller you can use ModelState.IsValid . Model validation in ASP.NET Core is a useful resource (it targets MVC/Razor pages, but model validation still works in an API).

You can probably safely remove [FromForm] too.