kgrzybek/modular-monolith-with-ddd · warning · InvalidCommandException

Command validation error

Error message

Command validation error

What it means

Thrown by the UserAccess module ValidationCommandHandlerWithResultDecorator (TResult-returning variant). It runs all FluentValidation validators for command T, aggregates ErrorMessages, and throws InvalidCommandException(errors) with the literal message 'Command validation error'; the actionable detail is in Errors.

Source

Thrown at src/Modules/UserAccess/Infrastructure/Configuration/Processing/ValidationCommandHandlerWithResultDecorator.cs:33

        public ValidationCommandHandlerWithResultDecorator(
            IList<IValidator<T>> validators,
            ICommandHandler<T, TResult> decorated)
        {
            this._validators = validators;
            _decorated = decorated;
        }

        public Task<TResult> Handle(T command, CancellationToken cancellationToken)
        {
            var errors = _validators
                .Select(v => v.Validate(command))
                .SelectMany(result => result.Errors)
                .Where(error => error != null)
                .ToList();

            if (errors.Any())
            {
                throw new InvalidCommandException(errors.Select(x => x.ErrorMessage).ToList());
            }

            return _decorated.Handle(command, cancellationToken);
        }
    }
}

View on GitHub (pinned to 91c8ef24b4)

Solutions

1. Read ex.Errors for the specific failing validators (message is generic).
2. Fix the command values to pass validation.
3. Pre-validate on the client with the same rules.
4. Adjust validators if a valid value is wrongly rejected.

Example fix

// before
var userId = await _commandDispatcher.SendAsync(new AuthenticateCommand("", ""));

// after
var userId = await _commandDispatcher.SendAsync(new AuthenticateCommand(login, password));

var validator = new AuthenticateCommandValidator();
var result = await validator.ValidateAsync(cmd);
if (!result.IsValid) return BadRequest(result.Errors.Select(e => e.ErrorMessage));
var userId = await _commandDispatcher.SendAsync(cmd);

try { var userId = await _commandDispatcher.SendAsync(cmd); }
catch (InvalidCommandException ex)
{ return BadRequest(new { errors = ex.Errors }); } // message is generic; detail is in Errors

When it happens

Trigger: Sending a result-returning UserAccess command (e.g. authenticate, register user) with properties failing a registered validator.

Common situations: Authentication/register commands with empty login, weak password, or missing required fields.

Related errors

• Command validation error
• {validator error messages}
• {validator error messages}
• {validator error messages}
• {validator error messages}

AI-assisted analysis of kgrzybek/modular-monolith-with-ddd@91c8ef24b4 (2026-08-13). Data as JSON: /api/errors/c863ff440c63614d. Report an issue: GitHub.