Powershell C# cmdlet with parametersets with same subset of parameters

Question

I have defined the following parameter sets in MyCustomCmdlet with default parameterset as two :

    [Parameter(Mandatory = true, ParameterSetName = one)]
    [Parameter(Mandatory = true, ParameterSetName = two)]
    [Parameter(Mandatory = true, ParameterSetName = three)]
    [Parameter(Mandatory = true, ParameterSetName = four)]
    [ValidateNotNullOrEmpty]
    [Alias("a")]
    public string A { get; set; }

    [Parameter(Mandatory = true, ParameterSetName = two)]
    [ValidateNotNullOrEmpty]
    [Alias("b")]
    public string B { get; set; }

    [Parameter(Mandatory = true, ParameterSetName = three)]
    [SupportsWildcards]
    [ValidateNotNullOrEmpty]
    [Alias("c")]
    public string C { get; set; }


    [Parameter(Mandatory = true, ParameterSetName = four)]
    [ValidateNotNullOrEmpty]
    [Alias("d")]
    public string D { get; set; }


    [Parameter]
    [ValidateNotNullOrEmpty]       
    public string E{ get; set; }

    [Parameter]
    [ValidateNotNullOrEmpty]
    public string F { get; set; }

During debug, am getting expected number of parameter sets ie 4 with following parameters:

1.ParameterSetName: one Parameters: A , E, F

2.ParameterSetName: two Parameters: A, B , E, F

3.ParameterSetName: three Parameters: A, C , E, F

4.ParameterSetName: four Parameters: A, D , E, F

However, when I execute:

MyCustomCmdlet -A or MyCustomCmdlet -A -E -F

I am getting error stating, requires mandatory parameter B which is part of default parameter set.

1. Can someone please help me understand this behavior?
2. How to execute the cmdlet using parameter set "one"

Answer 1

PowerShell will try and resolve the ParameterSet based off the command given and will not try and resolve a non default ParameterSet unless there the default is not resolvable with the current inputs. In your scenario ParameterSet 'two' is default and Parameter A is part of that ParameterSet, so logically that's what PowerShell assumes you're targeting as the input is still valid for it. If you want the ability to provide Parameter A on it's own you need to create a ParameterSet with just Parameter A included, and this has to be default (ParameterSet 'one' in your example).

E and F do not have their ParameterSet property defined, so by default their ParameterSet is set to ParameterSet.AllParameterSets , so again including these two fields is valid for the default set, so PowerShell still assumes that's what you're trying to do.

Also PowerShell is case-insensitive, so you don't need to Alias your parameters with the lower-case equivalent (if that is a representative scenario)