验证 c# 记录的属性

Question

record 是 C# 9 中的一种新对象类型。当需要不可变对象时，它可以节省大量输入。在某些情况下，可能需要验证记录的属性。在this question 中，提出了一种模式。该解决方案有效，但我认为我找到了一种更优雅的方式（请参阅我的回复）。我建议：

record Person(string FirstName, string LastName, int Age, Guid Id)
{
    private bool _dummy = 
        Check.StringArg(FirstName) && Check.StringArg(LastName) && Check.IntArg(Age);

    internal static class Check
    {
        static internal bool StringArg(string s)
        {
            if (s == "" || s == null)
                throw new ArgumentException("Argument cannot be null or empty");
            else return true;
        }

        static internal bool IntArg(int a)
        {
            if (a < 0)
                throw new ArgumentException("Argument cannot be negative");
            else return true;
        }
    }
}

这个想法是使用编译器生成的属性，如果有什么不对的话，有一些验证函数会抛出异常。不幸的是，有无意义的 _dummy 变量。有没有办法摆脱它？

Answer 1

这是一个绝妙的想法，它激发了我围绕这个想法实现一种基于扩展方法的验证框架。 我创建了以下验证类（为简洁起见删除了其他验证）：

public static class Validation
{
    public static bool IsValid<T>(this T _)
    {
        return true;
    }
    public static T NotNull<T>(T @value, [CallerArgumentExpression("value")] string? thisExpression = default)
    {
        if (value == null) throw new ArgumentNullException(thisExpression);
        return value;
    }

    public static string LengthBetween(this string @value, int min, int max, [CallerArgumentExpression("value")] string? thisExpression = default)
    {
        if (value.Length < min) throw new ArgumentOutOfRangeException(thisExpression, $"Can't have less than {min} items");
        if (value.Length > max) throw new ArgumentOutOfRangeException(thisExpression, $"Can't have more than {max} items");
        return value;
    }

    public static IComparable<T> RangeWithin<T>(this IComparable<T> @value, T min, T max, [CallerArgumentExpression("value")] string? thisExpression = default)
    {
        if (value.CompareTo(min) < 0) throw new ArgumentOutOfRangeException(thisExpression, $"Can't have less than {min} items");
        if (value.CompareTo(max) > 0) throw new ArgumentOutOfRangeException(thisExpression, $"Can't have more than {max} items");
        return value;
    }
}

然后您可以将其与以下内容一起使用：

// FirstName may not be null and must be between 1 and 5
// LastName may be null, but when it is defined it must be between 3 and 10
// Age must be positive and below 200
record Person(string FirstName, string? LastName, int Age, Guid Id)
{
    private readonly bool _valid = Validation.NotNull(FirstName).LengthBetween(1, 5).IsValid() &&
        (LastName?.LengthBetween(2, 10).IsValid() ?? true) &&
        Age.RangeWithin(0, 200).IsValid();
        
}

?? true 非常重要，这是为了确保在可为空的 LastName 确实为空的情况下继续验证，否则它会短路。 也许使用另一个静态 AllowNull 方法来包装该变量的整个验证会更好（更安全），如下所示：

public static class Validation
{
    public static bool IsValid<T>(this T _)
    {
        return true;
    }
    public static bool AllowNull<T>(T? _)
    {
        return true;
    }
    public static T NotNull<T>(T @value, [CallerArgumentExpression("value")] string? thisExpression = default)
    {
        if (value == null) throw new ArgumentNullException(thisExpression);
        return value;
    }

    public static string LengthBetween(this string @value, int min, int max, [CallerArgumentExpression("value")] string? thisExpression = default)
    {
        if (value.Length < min) throw new ArgumentOutOfRangeException(thisExpression, $"Can't have less than {min} items");
        if (value.Length > max) throw new ArgumentOutOfRangeException(thisExpression, $"Can't have more than {max} items");
        return value;
    }

    public static IComparable<T> RangeWithin<T>(this IComparable<T> @value, T min, T max, [CallerArgumentExpression("value")] string? thisExpression = default)
    {
        if (value.CompareTo(min) < 0) throw new ArgumentOutOfRangeException(thisExpression, $"Can't have less than {min} items");
        if (value.CompareTo(max) > 0) throw new ArgumentOutOfRangeException(thisExpression, $"Can't have more than {max} items");
        return value;
    }
}

record Person(string FirstName, string? LastName, int Age, Guid Id)
{
    private readonly bool _valid = Validation.NotNull(FirstName).LengthBetween(1, 5).IsValid() &&
        Validation.AllowNull(LastName?.LengthBetween(2, 10)) &&
        Age.RangeWithin(0, 200).IsValid();
}

仍然不太喜欢那部分，但除此之外，我认为它很酷！虽然还没有实际测试过：）所以要小心！