Web API [FromBody] parameter is null when sending an array of objects

Question

I seem to have run into an interesting problem with Web API - using this controller action, with a breakpoint on the opening brace to inspect thing:

[HttpPut]
public void Test([FromBody]object thing)
{
}

If I submit the following request (as CURL), I get the expected value which is a JObject containing the data from the body:

curl -X PUT -H "Content-Type: application/json" -d '{
    "Name": "Joe",
    "Key": { "Key": "Value" }
}' "http://localhost/api/TestController/Test"

That is, an anonymous object where Name is Joe and Key is another object containing Key = Value.

However, if I change this ever-so-slightly to instead submit an array of Keys, I get null. No error, just null.

curl -X PUT -H "Content-Type: application/json" -d '{
    "Name": "Joe",
    "Keys": [{ "Key": "Value" }]
}' "http://localhost/api/TestController/Test"

Why is this happening? The HTTP verb doesn't seem to matter (I've tried POST and PUT), and using dynamic instead of object is the same thing.

Here's some screenshots:

oɔɯǝɹ · Accepted Answer · 2016-07-11 22:03:31Z

2

Your code is working fine when testing in Postman.

edited Jul 11, 2016 at 22:03

oɔɯǝɹ

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answered Jul 11, 2016 at 18:04

Win

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3 Comments

Dmitrii Dovgopolyi Over a year ago

@Win This is not an answer. I don't think comminucating with OP through answers is the right way. Please, use comments

Win Over a year ago

@DmitryDovgopoly We cannot post the screenshots inside the comment. Didn't I say that this was not and answer. Instead, OP figured out the problem, because of my post. End of the day, we are trying to help each other instead of arguing what real answer should look like.

Dmitrii Dovgopolyi Over a year ago

Your answer helped to solve the problem. No arguing about that. But helping one person is not the only goal. Another is to help people who have the same problem. And right now the top answer to the question is not a solution and won't help. In that way it should be removed (by SO rules). And if it will be removed, then your help (not only the answer, but the comments also) will be lost.

Scott · Accepted Answer · 2016-07-11 18:13:36Z

1

Turns out I had the global JSON setting for MaxDepth set to 2 elsewhere in my code, which was running before the controller action. Why this returns null and not an empty object is still beyond me, but changing this to 3 corrects the issue and functions as expected.

Sorry for the confusion everyone, thanks for the answers!

answered Jul 11, 2016 at 18:13

Scott

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Comments

Erez.L · Accepted Answer · 2016-07-11 18:36:25Z

1

i think it all depends on how you wish to work with it, if you want to get a strongly typed model you can always create one like user3658685 said.

another thing you can do is bind the data to JObject and then serialize using Newton-soft Serializer:

public void Post([FromBody] JObject value)
{ 
    //instead of object you can use any type you wish to cast
    object obj = value.ToObject<object>();
}

answered Jul 11, 2016 at 18:36

Erez.L

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Comments

user3658685 · Accepted Answer · 2016-07-11 18:16:00Z

0

WebApi uses model mapping class to try to map json object with the argument og your WebApi method. You can resolve this by creating a class with all attributes matching your json object.

public class Contract {
   public string Name { get; set; }
   public dynamic[] Keys { get; set; }
}

And changing the signature of your WebApi method with

public void Post([FromBody] Contract value)
{
}

answered Jul 11, 2016 at 18:16

user3658685

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