Trying to call json ID in MVC controller but I am getting this error "Object reference not set to an instance of an object"

Question

I am trying to get ID from a json file in an ASP.NET MVC controller but for some reason it gives me "Object reference not set to an instance of an object." error. JsonFile:

"Id": "1",
"FirstName": "FirstName",
"LastName": "LastName",
"Age": "21",

C# class:

public class User
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}

ASP.NET MVC controller:

model = UserRepository.GetUserById(User.Id);   // error line

Does this answer your question? [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — haldo, Jul 18 '20 at 06:37
@haldo I understand why the error is coming from your attached link but I can't find a solution for it. — Kazuma, Jul 18 '20 at 06:49
You should change `Id` and `Age` in your json data to numbers as they are `string`s as of now. — Streamline, Jul 18 '20 at 06:51
Can you share the code which converts json to the user objects? — Chetan Ranpariya, Jul 18 '20 at 06:57
@ChetanRanpariya I think I haven’t convert the json to user object but I do have a class which I have shown in the question. — Kazuma, Jul 18 '20 at 07:00

score 1 · Accepted Answer · answered Jul 18 '20 at 07:20

First you should change Id and Age to numbers, otherwise the model binder will give you an exception. Something like this:

The JSON value could not be converted to System.Int32. Path: $.Id | LineNumber: 0 | BytePositionInLine: 11 `

Your JSON should now look like this:

{
    "Id": 1,
    "FirstName": "FirstName",
    "LastName": "LastName",
    "Age": 21
}

Then you should add a parameter User user to your action instead of declaring the user variable as property of the controller like you probably did as you said in one of your comments.

You should end up with something along these lines:

[HttpPost]
public string MyAction(User user)
{
    if (user is null)
        return "Bad request :(";

    // Do things with user.

    return $"Id: {user.Id}, First Name: {user.FirstName}, Last Name: {user.LastName}, Age: {user.Age}";
}

Trying to call json ID in MVC controller but I am getting this error "Object reference not set to an instance of an object"

1 Answers1