Sending empty array to webapi

Question

I want to POST an empty javascript array [] to webAPI and have it create an empty list of integers. I also want it so if I post javascript null to webAPI that it assigns null to the list of integers.

JS:

var intArray = [];
$.ajax({
 type: 'POST',
 url: '/api/ListOfInts',
 data: {'' : intArray},
 dataType: 'json'
});

c# webapi

[HttpPost]
public void ListOfInts([FromBody]List<int> input)

Problem 1) Jquery refuses to send data {'' : []} as the post payload. As soon as I add something in the array it works such as {'' : [1,2,3]}

Problem 2) Passing empty js array to controller gives null Based on what i read even if I do get it to post an empty array, it will initialize the list as null. Discussed solutions have it so that the list is always initializes as empty but I don't want that. I want it to be null in some case (when null/undefined is sent to it) and when [] is sent it should initialize as empty.

Edit: See https://www.asp.net/web-api/overview/advanced/sending-html-form-data-part-1 about why I am using {'' : []}

• Aleksey L.: Have you tried to send just data: intArray ?
• LearningJrDev: Yes, it doesnt work at all. WebAPI doesnt know how to handle it
• jensendp: In WebApi, differentiating between null and empty in a request can be difficult. If you are using those to somehow set some sort of "state" in your application, I would rethink how you are doing it. Possibly sending some sort of flag or something that will properly initialize your list on the server.

Answer 1

Use JSON.stringify(intArray) and contentType: 'application/json' works for me:

$.ajax({
 url: "/api/values",
 method: "POST",
 contentType: 'application/json',
 data: JSON.stringify([])
});

enter image description here

$.ajax({
 url: "/api/values",
 method: "POST",
 contentType: 'application/json',
 data: null
});

enter image description here

$.ajax({
 url: "/api/values",
 method: "POST",
 contentType: 'application/json',
 data: JSON.stringify([1, 2, 3])
});

enter image description here

Answer 2

data: {'' : intArray},

a blank key name is not allowed in JSON.

Just send the array itself.

data: intArray,

• LearningJrDev: This is required by webAPI when sending a valuetype
• zastrowm: According to this question and answer, empty keys are allowed.

Answer 3

1. Use JSON.stringify() to convert javascript object to JSON string.

2. Use contentType: 'application/json' as it is correct MIME media type for JSON. What is the correct JSON content type?

3 dataType is not necessary

data: JSON.stringify(intArray), contentType: 'application/json'