.NET 6 What is the best way to make properties required and non-null in records

Question

I searched for an answer for it and couldn't find a clear answer. And yes, I know that similar questions exist everywhere. I hope I can get an answer here.

Let's assume I have a Person class with 2 properties (FirstName, MiddleName). FirstName is required & MiddleName is optional.

I want the FirstName property to always have non-nullable data.

Here are some options I think of (but none of them seems to be perfect).

One optional way would be to use the short syntax of records:

// FirstName might be null (bad)
// MiddleName is optional (good)
public record Person(string FirstName, string? MiddleName);

Another way would be to use the null-forgiving operator, but still the same problem.

// FirstName might be null (bad)
// MiddleName is optional (good)
public record Person
{
    public string FirstName { get; init; } = null!;

    public string? MiddleName { get; init; }
}

The old option would be to check the input in the constructor:

// FirstName is required and will always have some data (good)
// MiddleName is optional (good)
// Long syntax (bad)
public record Person
{
    public string FirstName { get; init; }

    public string? MiddleName { get; init; }

    public Person(string firstName, string? middleName)
    {
        // Probably it would be better to check if it is NullOrWhiteSpace.
        ArgumentNullException.ThrowIfNull(firstName);

        FirstName = firstName;
        MiddleName = middleName;
    }
}

If the last option is the way to enforce a non-null value, then I would ask:

1. With all the new shortened syntax, is it really the way we should do it?
2. When should I use the shortened way of writing records? (I would always want to validate that required fields have values and do it in the constructor).

Answer 1

In C# 11.0 preview it is possible to use required in the property declaration.

public record Person
{
    public required string FirstName { get; init; }

    public string? MiddleName { get; init; }
}

A good explanation article about it can be found here.

Answer 2

i would probably go for the classic way of just enforcing it on the constructor. don't really see the downsides of that when FirstName is always required

Answer 3

The best possible solution with minimum overengineering is an old simple constructor, so your code in the question is the best possible solution. Why?

Neither nullable reference types, nor a record, nor required guarantees that a property will not be a null.

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Nullabe reference types is a static analysis tool. It doesn't ensure anything in runtime. It is just information for a developer that null should be handled properly.

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The required members in C# 11 does not work on .NET 6. It is by design, see the GitHub issue here.

There are missing attributes RequiredMemberAttribute and CompilerFeatureRequiredAttribute in .NET 6, see the framework reference.

In addition, required keyword just enforce passing a value to the property, but it doesn't say anything what the value should or should not be. You can pass null there easily. You will get a warning if you have nullable reference types turn on, but that is it.

The marked ✅ answer is completely wrong here.

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A record doesn't give you anything here and it is not a good use case for a record when you have to write non-trivial logic to a constructor.