How do I return JSON from an Azure Function

I am playing with Azure Functions. However, I feel like I'm stumped on something pretty simple. I'm trying to figure out how to return some basic JSON. I'm not sure how to create some JSON and get it back to my request.

Once upon a time, I would create an object, populate its properties, and serialize it. So, I started down this path:

#r "Newtonsoft.Json"

using System.Net;

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
    log.Info($"Running Function");    
    try {      
      log.Info($"Function ran");

      var myJSON = GetJson();

      // I want myJSON to look like:
      // {
      //   firstName:'John',
      //   lastName: 'Doe',
      //   orders: [
      //     { id:1, description:'...' },
      //     ...
      //   ]
      // }
      return ?;
    } catch (Exception ex) {
        // TODO: Return/log exception
        return null;
    }
}

public static ? GetJson() 
{
  var person = new Person();
  person.FirstName = "John";
  person.LastName = "Doe";

  person.Orders = new List<Order>();
  person.Orders.Add(new Order() { Id=1, Description="..." });

  ?
}

public class Person 
{
  public string FirstName { get; set; }
  public string LastName { get; set; }
  public List<Order> Orders { get; set; }
}

public class Order
{
  public int Id { get; set; }
  public string Description { get; set; }
}

However, I'm totally stuck on the serialization and return process now.I guess I'm used to returning JSON in ASP.NET MVC where everything is an Action

Here's a full example of an Azure function returning a properly formatted JSON object instead of XML:

#r "Newtonsoft.Json"
using System.Net;
using Newtonsoft.Json;
using System.Text;

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
    var myObj = new {name = "thomas", location = "Denver"};
    var jsonToReturn = JsonConvert.SerializeObject(myObj);

    return new HttpResponseMessage(HttpStatusCode.OK) {
        Content = new StringContent(jsonToReturn, Encoding.UTF8, "application/json")
    };
}

Navigate to the endpoint in a browser and you will see:

{
  "name": "thomas",
  "location": "Denver"
}

The easiest way is perhaps to

public static async Task<IActionResult> Run(
    [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "/jsontestapi")] HttpRequest req,
    ILogger log)
{
    return new JsonResult(resultObject);
}

Will set the content-type to application/json and return the json in the response body.

You can take req from

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)

and create the response using

return req.CreateResponse(HttpStatusCode.OK, json, "application/json");

or any of the other overloads in assembly System.Web.Http.

More info on docs.microsoft.com

It looks like this can be achieved just by using the "application/json" media type, without the need to explicitly serialize Person with Newtonsoft.Json.

Here is the full working sample that results in Chrome as:

{"FirstName":"John","LastName":"Doe","Orders":[{"Id":1,"Description":"..."}]}

The code is given as below:

[FunctionName("StackOverflowReturnJson")]
    public static HttpResponseMessage Run([HttpTrigger("get", "post", Route = "StackOverflowReturnJson")]HttpRequestMessage req, TraceWriter log)
    {
        log.Info($"Running Function");
        try
        {
            log.Info($"Function ran");

            var myJSON = GetJson();  // Note: this actually returns an instance of 'Person' 

            // I want myJSON to look like:
            // {
            //   firstName:'John',
            //   lastName: 'Doe',
            //   orders: [
            //     { id:1, description:'...' },
            //     ...
            //   ]
            // }
            var response = req.CreateResponse(HttpStatusCode.OK, myJSON, JsonMediaTypeFormatter.DefaultMediaType); // DefaultMediaType = "application/json" does the 'trick'
            return response;
        }
        catch (Exception ex)
        {
            // TODO: Return/log exception
            return null;
        }
    }

    public static Person GetJson()
    {
        var person = new Person();
        person.FirstName = "John";
        person.LastName = "Doe";

        person.Orders = new List<Order>();
        person.Orders.Add(new Order() { Id = 1, Description = "..." });

        return person;
    }

    public class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public List<Order> Orders { get; set; }
    }

    public class Order
    {
        public int Id { get; set; }
        public string Description { get; set; }
    }

JSON is pretty easy, Newtonsoft.Json library is a special case. You can include it by adding this at the top of the script file:

#r "Newtonsoft.Json"

using Newtonsoft.Json;

Then your function becomes:

public static string GetJson() 
{
  var person = new Person();
  person.FirstName = "John";
  person.LastName = "Doe";

  person.Orders = new List<Order>();
  person.Orders.Add(new Order() { Id=1, Description="..." });

  return JsonConvert.SerializeObject(person);
}

You can change the method signature into:

public static async Task<object> Run(HttpRequestMessage req, TraceWriter log)

and it will allow JSON data to be returned.

I had a similar issue and this seemed to be the most popular post with no answer. After figuring what node does the below should work and give you exactly what you are after. The other examples still returns a string representation wheres this will return JSON.

Remember to declare using System.Text; and also add:

return JsonConvert.SerializeObject(person);

to the GetJson function as per Juunas response.

    return new HttpResponseMessage(HttpStatusCode.OK)
       {
           Content = new StringContent(GetJson(), Encoding.UTF8, "application/json")
       };

#r "Newtonsoft.Json"

using System.Net;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Primitives;
using Newtonsoft.Json;

public static IActionResult Run(HttpRequest req, ILogger log)
{    
    (string name, string surname) = ("James", "Ozzy");
    return new ObjectResult(new { name, surname }) ;
 }