C# Web API POST parameter FromBody is always null

Question

I've been scouring the web for hours and tried many different solutions also described here on StackOverflow. I know similar questions have been asked before, but none of the answers or comments have worked for me.

The problem: I have a .NET Web API that has a Post-method with some parameters. One of the parameters is a complex object that is supposed to be read from the body (that is JSON). However, this object is always null.

This is my code:

// POST api/worksheets/post_event/true/false
        [Route("post_event/{newWorksheet}/{eindEvent}")]
        [HttpPost]
        public Event Post(bool newWorksheet, bool eindEvent, [FromBody] Event eventData)
        {
            return eventData;
        }

To be clear: eventData is the object that's always null. The boolean values are read correctly.

The full request body is:

POST http://localhost:5000/api/worksheets/post_event/true/false
Content-Type: application/json
{"Persnr":1011875, "WorksheetId":null, "Projectnr":81445, "Uursoort":8678, "Tijd":{"09-08-2016 9:25"}}

And for reference, this is the Event-class:

public class Event
    {
        public long Persnr { get; set; }
        public int WorksheetId { get; set; }
        public int Projectnr { get; set; }
        public int Uursoort { get; set; }
        public DateTime Tijd { get; set; }
    }

Some of the things I've already tried:

Change JSON to different formats (only values, "Event": {} surrounding the actual object, an = in front of the JSON).
Test with just the Event parameter (removing the others as well as in the route)
Add a default ctor to Event.
Remove the [FromBody] tag. If I do this, the Event-object is not null, but all the properties are. Properties can be filled through the URI, but that is not the desired behavior.

According to all solutions and documentation I have read, it should simply work the way I have it displayed above. What am I missing?

I believe the Jsonserializer will translate that to 0 automatically, doesn't it? — Devvox93, Aug 09 '16 at 21:51
Most likely, make sure your event is bound to the right namespace you could be tied to a different class in your controller — johnny 5, Aug 09 '16 at 22:27
It was in fact a combination of your answer about the int (shouldn't pass null but 0) and the datetime should be without brackets/braces. — Devvox93, Aug 10 '16 at 08:20

score 1 · Accepted Answer · answered Aug 09 '16 at 15:20

1

Your json object is invalid. My suggestion is to always run json object written manually through a json parser like this: http://json.parser.online.fr/

"Tijd":{"09-08-2016 9:25"}

should instead be

"Tijd":["09-08-2016 9:25"]

answered Aug 09 '16 at 15:20

jimmy

1,981
3
19
28

It worked without the brackets or braces (so just `"09-08-2016 9:25"`). Thanks also for your link to the Parser. It helped :) The thing was, I had 2 mistakes. The date, but also the int value. It mustn't be null, but 0. It should have just parsed the correct values, at least then I could have seen the problem is with those specific fields. – Devvox93 Aug 10 '16 at 08:22
@DevvoX I assumed that you were trying to make an array of times since you had added the braces ;) – jimmy Aug 10 '16 at 09:04

score 1 · Answer 2 · answered Sep 13 '17 at 11:30

This usually happens when your object can't be deserialized from JSON request.

The best practice would be to make sure that all the request properties can accept null values (make value types properties are nullable). And then you can validate that all needed request properties are provided, or return 400 error if not. This way you at least will be able to understand what request property causes the problem.

Pavel Tsybulivskyi · Answer 3 · 2016-08-09T15:50:36.273

0

The right JSON for this type should be just

{"Persnr":1011875, "WorksheetId":null, "Projectnr":81445, "Uursoort":8678, "Tijd":"09-08-2016 9:25"}

No curly braces for Tijd, because Tijd is plain DateTime property that can be inferred from string, representing DateTime

edited Aug 09 '16 at 15:50

answered Aug 09 '16 at 15:43

Pavel Tsybulivskyi

314
1
10

Well I assume the purpose of the curly braces was to have an array of several time objects. So instead of removing the braces he should use brackets. – jimmy Aug 10 '16 at 07:06
It was in fact a combination of your answer about the date (shouldn't pass with braces/brackets) and the int value should be 0, not null. – Devvox93 Aug 10 '16 at 08:16

C# Web API POST parameter FromBody is always null

3 Answers3

Linked