Argument Models

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[ApplicationMetadata(Name="send", Description="sends email")]
public void SendEmail([Option]string subject, [Option(ShortName="a")]List<string> attachments, [Option]string body, [Argument]string from, [Argument]string to)
{

}

this can be invoked from the shell with:

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send --subject hi -a "myFile.txt" -a "important.docx" --body "just wanted you to review these files" bilal@bilal.com john@john.com

The same arguments can be defined with a class:

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public class Email : IArgumentModel
{
    [Option]
    public string Subject {get;set;}

    [Option(ShortName="a")]
    public List<string> Attachments {get;set;}

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

    [Argument]
    public string From {get;set;}

    [Argument]
    public string To {get;set;}
}

and

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[ApplicationMetadata(Name="send", Description="sends email")]
public void SendEmail(Email email)
{

}

Benefits of argument models:#

  • Common arguments can be extracted to models to enforce contracts across commands.
    ex. DryRunModel ensures the same short name, long name, description, etc are consistent across all commands using this model.
  • FluentValidation framework can be used to validate the model

Caveat#

Argument position cannot be guaranteed to be consistent because the .Net Framework does not guarantee the order properties are reflected.

The GetProperties method does not return properties in a particular order, such as alphabetical or declaration order. Your code must not depend on the order in which properties are returned, because that order varies.

Order can differ on each machine the app is deployed to.

This is not an issue with Option because options are positional

Recommendation#

  • Avoid modelling arguments in argument models unless you need to validate them using FluentValidation.
  • If you do need to model arguments and you have scripts in place, verify the scripts work as expected on each new machine, after .net framework updates and after new deployments.

Last update: February 22, 2020