c# Nested data class is not recognized and gives error "Object reference not set to an instance of an object." [duplicate]

Question

I have this simple application to populate fields from a data model, The data model is called Order which has a nested class called Address. When I attempt to assign a value to Order.Address.city, I get the error message:

Object reference not set to an instance of an object.

I tried various different ways to correct the error, Order class doesn't seem to recognize the Address class.

Data Model is listed below....

namespace ConsoleApp1.DataModels
{
    public class Order { 
        public string name { get; set; }
        public string description { get; set; }
        public Address address { get; set; }

        
        public class Address 
        {
            public string city { get; set; }
            public string state { get; set; }
            public string zip { get; set; }
        }
    }
 }

C# code is below and error occurs when this line is executed:

myOrder.address.city = "Chicago";

using ConsoleApp1.DataModels;


namespace WalmartOrderProcessing
{
    class Program
    {
         static void Main(string[] args)
        {
            Order myOrder = new Order();

            myOrder.name = "John Doe";
            myOrder.description = "Contractor";

            myOrder.address.city = "Chicago";
            myOrder.address.state = "IL";
            myOrder.address.zip = "12345";
        }
    }
}

you have not initialized the Address property anywhere. That's why it's null. — Ivan Petrov
– Ivan Petrov, Commented Jun 8, 2024 at 14:54
this should work public Address address { get; set; } = new Address(); — Ivan Petrov
– Ivan Petrov, Commented Jun 8, 2024 at 14:56
A nested class nests the definition of the class within another class. When you instantiate an object of the parent class, the newly created object doesn't automatically instantiate a (or perhaps many) instance(s) of the nested class. You need to do that yourself (as everyone else has pointed out) — Flydog57
– Flydog57, Commented Jun 8, 2024 at 15:35

Mureinik · Accepted Answer · 2024-06-08 14:55:21Z

0

You aren't initializing the address member, so implicitly it's null. Initialize it and you should be fine:

public Address address { get; set; } = new Address();

answered Jun 8, 2024 at 14:55

Mureinik

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