BeforeExecute() & Parameter Validation

Sample Code / Project

The CommandBase class provides several methods that can be overridden. Check the class documentation for more information. One of the most important methods is BeforeExecute.

In the BeforeExecutemethod you can check if there is an unresolved property and/or you can provide dynamic default values.

protected override void BeforeExecute(
    TCommandParameters ps,
    HashSet<string> unresolvedPropertyNames,
    ErrorDetailList errors)
{
    // Check K.O. criteria: do not run command if fail
    DateTime minStartDate = new DateTime(2020, 1, 1);
    if (ps.StartDate < minStartDate)
    {
        errors.AddError(nameof(ps.StartDate),
            $"{nameof(ps.StartDate)} must be greater or equal to
            {minStartDate:d}, current value: {ps.StartDate:d}");
}

The HashSet<string> unresolvedProperties contains all annotated properties which have not been resolved. For example, imagine, you have defined am optional Option called "EndDate". If this Option is not provided in the command-line the Property DateTime EndDate would be: DateTime.DefautlValue, and this is probably not what you wanted.

[OptionDescriptor("EndDate", Required = false)]
public DateTime EndDate { get; set; }

You can catch this in the BeforeExecute method and check if any Property (Contains( nameof(ps.EndDate)) !!) ****is unresolved - has not got a value from command-line - neither explicitly provided nor static default value:

if (unresolvedPropertyNames.Contains(nameof(ps.EndDate)))
{
    // Set dynamic, dependent default value
    Console.WriteLine($"Unresolved {nameof(ps.EndDate)}");
    ps.EndDate = ps.StartDate.AddDays(7);
}

Error Handling

Use the errors.AddError() method to collect errors message. Commander will check for any error before it executes the Command and terminates the application gracefully, by printing out all error messages you collected. Collecting error messages is much more convenient the throwing Exceptions, because an Exception normally stop after the first error occurred.