How to return a Json from a .Net Core Web API?

Question

This is a basic question. I am new to ASP.Net Core so I created a .Net Core Web API project using the template in Visual Studio 2017 and I would like to know how to return a Json string from the Get() function.

The Get() function provided.

    [HttpGet]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2" };
    }

I would like to know how to change so it returns a Json string of int variable like the following.

    // GET: api/MOER
    [HttpGet]
    public <<some return type>> Get()
    {
        _MOER = 32;

        return <<return a Json result/string of _MOER>>;
    }

I am have seen the Nuget package Newtonsoft.Json where you serialize/deserialize but I am not sure if its applicable any more with .Net Core.

I have also seen examples where they use JsonResult but when I try to use this approach, the compiler doesn't know what Json() is.

    [HttpGet]
    public JsonResult Get()
    {
        _MOER = 32;

        return Json(_MOER);
    }

Thank you for your help!

It seems that you're using the [ApiController], why not simply return an IActionResult type? — itminus
– itminus, Commented Nov 20, 2018 at 1:40

HaukurHaf · Accepted Answer · 2018-11-19 22:55:54Z

17

Add this attribute to your controller class:

[Produces("application/json")]

So it becomes:

[Produces("application/json")]
public class YourController: Controller {

   [HttpGet]
   public IEnumerable<string> Get()
   {
       return new string[] { "value1", "value2" };
   }
}

That should be enough, otherwise I believe the default is XML (unless the client explicitly asks for JSON using the Accept HTTP header).

answered Nov 19, 2018 at 22:55

HaukurHaf

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5 Comments

PKonstant Over a year ago

Ok but I would like to know how to return a Json string so it returns something like { "key":"value"}

HaukurHaf Over a year ago

Then you need to change your method so it returns a key/value type, like a Dictionary<string, string>. A list of strings will just be serialized to a plain string array.

PKonstant Over a year ago

Can't I just use the Newtonsof.Json's Serialize/Deserialize for returning a class? (So you know, I'm not interested returning "value1", "value2")

PKonstant Over a year ago

oh, so you are saying if I return a Dictionary, then it will return as a json string. So does that mean everything returned by a Get are always in json string?

HaukurHaf Over a year ago

Yes, it will always return whatever the return type is, serialized to JSON. If you have a class called Foo with two string properties, Bar and Baz, the result will be: { "Bar":"value of bar", "Baz":"value of baz" } Just try it out!

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