How can I have Nullable<T>

Question

    public interface IOperationResult
    {
        bool IsSuccessful { get; set; }
        public string Message { get; set; }
    }

    public interface ICreateCommandOperationResult<T?> : IOperationResult
    {
        public T? InsertedId { get; set; }
    }

When I insert a record in database, I want to return inserted record's Id. But sometimes there are exceptions that in this case I need to send null in InsertedId.

How can I do it?

Make your ICreateCommandOperationResult generic on T (i.e., ICreateCommandOperationResult<T>), constrain T to a struct and then use T? as the type of InsertedId — Flydog57
– Flydog57, Commented Mar 28, 2020 at 21:24

Pavel Anikhouski · Accepted Answer · 2020-07-17 12:14:52Z

1

You can apply the where T: struct generic constraint (or class if you are using C# 8 and need a nullable reference types) and replace T? with just T in ICreateCommandOperationResult interface.

public interface ICreateCommandOperationResult<T> : IOperationResult
    where T : struct //where T : class
{
    public T? InsertedId { get; set; }
}

The example of implementation

public class Test : ICreateCommandOperationResult<int>
{
    public bool IsSuccessful { get; set; }
    public string Message { get; set; }
    public int? InsertedId { get; set; }
}

edited Jul 17, 2020 at 12:14

answered Mar 28, 2020 at 21:22

Pavel Anikhouski

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3 Comments

Hamid Noahdi Over a year ago

The compiler was happy about struct but not about class

Pavel Anikhouski Over a year ago

@Enigmativity yes, I've pointed it in aswer, that it's valid in C#8 in case of using nullable reference types

Enigmativity Over a year ago

@PavelAnikhouski - Yes, Pavel, my comment was directed at Hamid. He may not have understood that.

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