Note on fixing the problem where ASP.NET Core 2 API controller always reports NULL during POST requests

A quick note on creating Web API controllers with ASP.NET Core 2: if you want to make sure your input data is automatically bound to correct HTTP POST body values, you must explicitly set the [FromBody] attribute for your input model object.

For example, if you had code like this:

public class MyApiController : Controller
{
    [HttpPost("api/somecontroller/somemethod")]
    public async Task PostSomeData(MyInputDataModel entry)
    {
        try
        {
            if (entry == null)
            {
                throw new ArgumentNullException(nameof(entry));
            }
            ...

…then you would notice that the "entry" parameter is never NULL, but all the properties inside it will be. In ASP.NET Core 2.0, the fix is simple, add the [FromBody] attribute before the input model object, like this:

public async Task PostSomeData([FromBody] MyInputDataModel entry)

If you have already upgraded to ASP.NET Core 2.1, then you have a new attribute called ApiController at your disposal. If you decorate your API controller with this attribute, you don't need to explicitly set the [FromBody] attribute.

Hope this helps!