Question

I’m trying to pass a collection of objects to the controller using $.post(); When I call the AddNewPerson() the C# side Friends collection has the right number of objects in it, but the properties are all blank.

Javascript:

function AddNewPerson(newPerson) {
    $.post("/Person/AddPerson/",
    {
        PersonName: newPerson.PersonName,
        PersonAge: newPerson.PersonAge,
        Friends:FriendList
    },
    function (JsonResponse) {
    });
}

C#

public JsonResult AddPerson(Person newPerson)
{
    Database.Add(newPerson);
}

Friends is a collection of Person

Javascript

function Person(Name, Age) {
    this.PersonName=Name; 
    this.Person.Age=Age; 
    this.FriendList=new Array();
}

C#

public class Person() 
{
    public Person()
    {
    }

    public string PersonName{get;set;}
    public string PersonAge{get;set;}
    public Person[] Friends { get; set; }
}

Answer 1

You could use a JSON request when you want to send complex structures like this:

var request = {
    personName: newPerson.PersonName,
    personAge: newPerson.PersonAge,
    friends: FriendList
};
$.ajax({
    // TODO: use a helper here, never hardcode urls
    url: '/Person/AddPerson/', 
    type: 'POST',
    contentType: 'application/json; charset=utf-8',
    data: JSON.stringify(request),
    success: function(result) {

    }
});

From your example it is not exactly clear how you are populating the FriendList variable that you are using but I guess it is something like this:

var friendList = new Array();
friendList.push({
    personName: 'john',
    personAge: 'smith'
});

The JSON.stringify method shown here is natively built into modern browsers but if you want to support legacy browsers you will need to include the json2.js script to your page.