JSON passed to ApiController doesn't deserialize string values

Question

I'm trying to pass a JSON array to an ApiController but the string values aren't deserializing (they are set to null values). The strange thing is that I still get the correct number of elements.

A have an ApiController:

[RoutePrefix("api/language")]
public class LanguagePairApiController : ApiController

With a post method:

// POST: api/language/create
[HttpPost]
[Route("create")]
public string Create([FromBody]LanguagePair[] languagePairs)

I'm sending JSON to it:

[
    {"Key":"Test","Value":"Test","Version":"1.0"},
    {"Key":"Areyousure","Value":"Are you sure?","Version":"1.0"},
    {"Key":"File","Value":"File","Version":"1.0"}
]

And this is the class I'm trying to map it to:

public class LanguagePair
{
    public string Key { get; set; }
    public string Value { get; set; }
    public string Version { get; set; }
}

But the string values are coming through as null:

What am I missing?
EDIT: I've figured out one answer to this and posted it below. But I'm still looking for a better answer...

I do not know much about asp.net, but isn't there some mechanism turned on that automatically camel cases object properties? Try to send [{"key":"win"}] to it. — Tamas Hegedus
– Tamas Hegedus, Commented Jun 21, 2016 at 22:44

Derek Tomes · Accepted Answer · 2016-06-21 22:47:39Z

2

I figured it out. I needed to decorate the class with DataContract and DataMember attributes:

{
    [DataContract]
    public class LanguagePair
    {
        [DataMember]
        public string Key { get; set; }
        [DataMember]
        public string Value { get; set; }
        [DataMember]
        public string Version { get; set; }
    }
}

answered Jun 21, 2016 at 22:47

Derek Tomes

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1 Comment

Dmitry Pavlov Over a year ago

If you'd like to adjust names for JSON properties (e.g. send {"myKey":"Areyousure","question event with space":"Are you sure?","v":"1.0"} ) you can use correspondingly: [DataMember(Name = "myKey")], [DataMember(Name = "question event with space")], [DataMember(Name = "v")] for the LanguagePair properties in C#

Nkosi · Accepted Answer · 2016-06-22 00:11:41Z

1

Read Parameter Binding in ASP.NET Web API

You need to remove [FromBody] attribute from your action...

// POST: api/language/create
[HttpPost]
[Route("create")]
public string Create(LanguagePair[] languagePairs) { ... }

and you can keep your class lean as you originally had it:

public class LanguagePair
{
    public string Key { get; set; }
    public string Value { get; set; }
    public string Version { get; set; }
}

Using [FromBody]

To force Web API to read a simple type from the request body, add the [FromBody] attribute to the parameter:
public HttpResponseMessage Post([FromBody] string name) { ... }
In this example, Web API will use a media-type formatter to read the value of name from the request body. Here is an example client request.
POST http://localhost:5076/api/values HTTP/1.1
User-Agent: Fiddler
Host: localhost:5076
Content-Type: application/json
Content-Length: 7

"Alice"
When a parameter has [FromBody], Web API uses the Content-Type header to select a formatter. In this example, the content type is "application/json" and the request body is a raw JSON string (not a JSON object).

answered Jun 22, 2016 at 0:11

Nkosi

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1 Comment

Derek Tomes Over a year ago

I just tried this and I get the same result (an array of 3 objects with all the values == null). But the [FromBody] is doing nothing - if I remove that and keep the [DataContract] it works correctly.

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