FluentValidation

Use FluentValidation with CommandDotNet to validate argument models.

TLDR, How to enable

.NET CLINuget Package Manager

dotnet add package CommandDotNet.FluentValidation

Install-Package CommandDotNet.FluentValidation

Enable with appRunner.UseFluentValidation(), or appRunner.UseFluentValidation(showHelpOnError: true)
to print help when there are validation errors.

Example

public class Program
{
    static int Main(string[] args) => AppRunner.Run(args);

    public static AppRunner AppRunner =>
        new AppRunner<Program>()
            .UseNameCasing(Case.LowerCase)
            .UseFluentValidation();

    public void Create(IConsole console, Table table, Host host, Verbosity verbosity)
    {
        console.WriteLine($"created {table.Name} as {host.Server}. notifying: {table.Owner}");
    }
}

public class Host : IArgumentModel
{
    [Option]
    public string Server { get; set; }
}

public class Table : IArgumentModel
{
    [Operand]
    public string Name { get; set; }

    [Option]
    public string Owner { get; set; }
}

public class Verbosity : IArgumentModel
{
    [Option('q')]
    public bool Quiet { get; set; }
    [Option('v')]
    public bool Verbose { get; set; }
}

public class HostValidator : AbstractValidator<Host>
{
    public HostValidator()
    {
        RuleFor(h => h.Server)
            .NotNull().NotEmpty()
            .Must(uri => Uri.TryCreate(uri, UriKind.Absolute, out _))
            .WithMessage("sever is not a valid fully-qualified http, https, or ftp URL");
    }
}

public class TableValidator : AbstractValidator<Table>
{
    public TableValidator()
    {
        RuleFor(t => t.Name).NotNull().NotEmpty().MaximumLength(10);
        RuleFor(t => t.Owner).NotNull().NotEmpty().EmailAddress();
    }
}

public class VerbosityValidator : AbstractValidator<Verbosity>
{
    public VerbosityValidator()
    {
        When(v => v.Verbose,
            () => RuleFor(v => v.Quiet)
                .NotEqual(true)
                .WithMessage("quiet and verbose are mutually exclusive. There can be only one!"));
    }
}

^{snippet source | anchor}

$ dotnet table.dll create TooLongTableName --server bossman --owner abc -qv
'Table' is invalid
  The length of 'Name' must be 10 characters or fewer. You entered 16 characters.
  'Owner' is not a valid email address.
'Host' is invalid
  sever is not a valid fully-qualified http, https, or ftp URL
'Verbosity' is invalid
  quiet and verbose are mutually exclusive. There can be only one!

^{snippet source | anchor}

If the validation fails, app exits with return code 2 and outputs validation error messages to error output.

Improve Perf

CommandDotNet tries to get the valdiator for each model from CommandContext.DependencyResolver. If not found, the assembly of the model is scanned (only once).

Register your validators with a container or provide a factory method.

public static AppRunner AppRunner =>
    new AppRunner<Program>()
        .UseNameCasing(Case.LowerCase)
        .UseFluentValidation(validatorFactory: model =>
        {
            switch (model)
            {
                case Host: return new HostValidator();
                case Table: return new TableValidator();
                case Verbosity: return new VerbosityValidator();
                default: return null;
            }
        });

^{snippet source | anchor}

vs. DataAnnotations

Comparing this example with the same example in DataAnnotations, the DataAnnotations is simpler to implement, requires less code, is easier to understand and has a cleaner error message your users.