Can't do Validation across multiple options

[xt1]

Great framework - love it - but I've run into a problem.

We have two separate options on a parameter set: ConnectionString and DbUser
If the ConnectionString is specified, DbUser is not required.
If the ConnectionString is not specified, then DbUser is required.
If neither is specified, then both are required.

A ValidationAttribute is only passed one variable at a time - there is no way to validate the set of options as a whole for consistency.
Or am I missing something?
There doesn't appear to be a good place to slot in an extra validation step, or to add a validation attribute to the class. :-(

[Arnab-Developer]

@xt1 I also faced the same problem. I solved this with FluentValidation library.

using Cocona;
using FluentValidation;
using Microsoft.Extensions.DependencyInjection;

var builder = CoconaApp.CreateBuilder();

builder.Services.AddTransient<IValidator<DatabaseParameters>, DatabaseParametersValidator>();

var app = builder.Build();

app.AddCommand("do-work", (DatabaseParameters databaseParameters,
    IValidator<DatabaseParameters> validator) =>
{
    var validationResult = validator.Validate(databaseParameters);

    if (validationResult.IsValid)
    {
        Console.WriteLine(databaseParameters.ConnectionString);
        Console.WriteLine(databaseParameters.DatabaseUser);
    }
    else
    {
        foreach (var error in validationResult.Errors)
        {
            Console.WriteLine(error.ErrorMessage);
        }
    }
});

await app.RunAsync();

internal record DatabaseParameters(string? ConnectionString, string? DatabaseUser)
    : ICommandParameterSet;

internal class DatabaseParametersValidator : AbstractValidator<DatabaseParameters>
{
    public DatabaseParametersValidator()
    {
        var errorMessage = "Connection string and database user both can't be empty.";

        RuleFor(x => x.ConnectionString).NotEmpty()
            .When(x => string.IsNullOrWhiteSpace(x.DatabaseUser)).WithMessage(errorMessage);

        RuleFor(x => x.DatabaseUser).NotEmpty()
            .When(x => string.IsNullOrWhiteSpace(x.ConnectionString)).WithMessage(errorMessage);
    }
}

There is another library called GuardClauses if you prefer exception based validation.

using Ardalis.GuardClauses; 
using Cocona;

var builder = CoconaApp.CreateBuilder();

var app = builder.Build();

app.AddCommand("do-work", (DatabaseParameters databaseParameters) =>
{
    try
    {
        Guard.Against.EmptyConnectionString(databaseParameters.ConnectionString,
            databaseParameters.DatabaseUser);

        Console.WriteLine(databaseParameters.ConnectionString);
        Console.WriteLine(databaseParameters.DatabaseUser);
    }
    catch (EmptyConnectionStringException ex)
    {
        Console.WriteLine(ex.Message);
    }
});

await app.RunAsync();

internal record DatabaseParameters(string? ConnectionString, string? DatabaseUser)
    : ICommandParameterSet;

internal static class DatabaseParametersGuardExtensions
{
    public static void EmptyConnectionString(this IGuardClause guardClause, string? connectionString,
        string? databaseUser)
    {
        if (string.IsNullOrWhiteSpace(connectionString) && string.IsNullOrWhiteSpace(databaseUser))
        {
            throw new EmptyConnectionStringException();
        }
    }
}

internal class EmptyConnectionStringException : Exception
{
    public EmptyConnectionStringException()
        : base("Connection string and database user both can't be empty.")
    {
    }
}