Nullable reference type in C#8 when using DTO classes with an ORM

Question

I activated this feature in a project having data transfer object (DTO) classes, as given below:

public class Connection     {         public string ServiceUrl { get; set; }         public string? UserName { get; set; }         public string? Password { get; set; }         //... others      } 

But I get the error:

CS8618: Non-nullable property 'ServiceUrl' is uninitialized. Consider declaring the property as nullable.

This is a DTO class, so I'm not initializing the properties. This will be the responsibility of the code initializing the class to ensure that the properties are non-null.

For example, the caller can do:

var connection = new Connection {   ServiceUrl=some_value,   //... } 

My question: How to handle such errors in DTO classes when C#8's nullability context is enabled?

Answer 1

You can do either of the following:

1. EF Core suggests initializing to null! with null-forgiving operator

   public string ServiceUrl { get; set; } = null! ; //or public string ServiceUrl { get; set; } = default! ; 

2. Using backing field:

   private string _ServiceUrl; public string ServiceUrl {     set => _ServiceUrl = value;     get => _ServiceUrl            ?? throw new InvalidOperationException("Uninitialized property: " + nameof(ServiceUrl)); } 

Answer 2

If it's non nullable, then what can the compiler do when the object is initialized?

The default value of the string is null, so you will

1. either need to assign a string default value in the declaration

   public string ServiceUrl { get; set; } = String.Empty;

2. Or initialize the value in the default constructor so that you will get rid of the warning

3. Use the ! operator (that you can't use)

4. Make it nullable as robbpriestley mentioned.