readme.md

Using FluentValidation NuGet package, create a custom validator to validate that Master.Children contain one of the names in Master.ValidNames

Example which goes not validate.

internal partial class Program
{
    static void Main(string[] args)
    {
        Master master = new()
        {
            FamilyName = "Smith",
            ValidNames = ["Jim", "Mary", "Karen"], 
            Children = [new Child { Name = "Mick" }]
        };

        CustomValidator validator = new();
        ValidationResult result = validator.Validate(master);

        Console.WriteLine();
        
        if (result.IsValid)
        {
            ...
        }
        else
        {
            ...
        }
    }
}

Child.cs

public class Child
{
    public string Name;
    public int Age;
}

Code.cs

Master master = new()
{
    FamilyName = "Smith",
    ValidNames = ["Jim", "Mary", "Karen"], 
    Children = [new Child { Name = "Mick" }]
};

Master.cs

public class Master
{
    public int Id { get; set; }
    public string FamilyName { get; set; }
    public List<string> ValidNames;
    public List<Child> Children;
}