Business Rules - apply to multiple fields and avoiding recursiveness.

gajit posted on Friday, August 24, 2012

Hi gents,

Haven't been here for some months which lays testament to how well I'm doing with CSLA 4.2 :)

I need some direction on a business rule that I want to implement.

For simplicity's sake, I basically have a form dialog that accepts several property values of a 'selection' object. This object is a businessbase object, with all of the things you would expect.

The fields are Every, Interval, StartDate, EndDate and NumberServices.

Basically, the user can change ANY of these fields and the bix objects needs to go fire a procedure that returns the other values accordingly.

The problem I have is that to fire any event on any of the changed properties, I assign a rule to the properties ( e.g. .PrimaryProperty=StartDate). The procedure returns new values to the other properties in the class and the propertychanged is raised on those and it becomes a never ending cycle.

There are essentially two issues I need to solve here - 1. to stop to recursive calls (can I somehow shortcircuit the propertychanged)  and 2. Is there a way to pass the PropertyName that has changed to my commandbase business rule? (Affects which properties are updated)

Here's what my code looks like:

    Protected Overrides Sub AddBusinessRules()
        MyBase.AddBusinessRules()

        With BusinessRules

            .AddRule(New CalculateServiceSeriesRule() With {.PrimaryProperty = EveryProperty})
            .AddRule(New CalculateServiceSeriesRule() With {.PrimaryProperty = IntervalProperty})
            .AddRule(New CalculateServiceSeriesRule() With {.PrimaryProperty = StartDateProperty})
            .AddRule(New CalculateServiceSeriesRule() With {.PrimaryProperty = EndDateProperty})
            .AddRule(New CalculateServiceSeriesRule() With {.PrimaryProperty = NumberServicesProperty})

        End With

    End Sub

and;

    Private Class CalculateServiceSeriesRule
        Inherits Csla.Rules.BusinessRule
        Protected Overrides Sub Execute(context As Csla.Rules.RuleContext)

            Dim target = DirectCast(context.Target, ServiceSeriesCreator)

            Dim _every As Integer = target.Every
            Dim _interval As String = target.Interval
            Dim _startdate As SmartDate = target.StartDate
            Dim _enddate As SmartDate = target.EndDate
            Dim _numberservices As Integer = target.NumberServices
            Dim _propertychanged As String = "Every" ' ** would like to pass the propertyname here ***

            ServiceSeriesCreator.CalculateServiceSeries( _
                                _propertychanged _
                                , _every _
                                , _interval _
                                , _startdate _
                                , _enddate _
                                , _numberservices _
                        )
            target.StartDate = _startdate
            target.EndDate = _enddate
            target.NumberServices = _numberservices

        End Sub
    End Class

Any help would be appreciated.

Thanks,

Graham

gajit replied on Friday, August 24, 2012

I believe I figured out on of the issues;

The propertyname I can derived as:

Dim _propertychanged As String = PrimaryProperty.Name

Curiously, the code appears to be working...

Can I confirm that I do in fact have a recursion issue? If whilst checking a value that has risen a PropertyChanged event, my routine updates other members of that BO, do they automatically get fired? If not, that's great.... 

Thanks,

Graham

JonnyBee replied on Friday, August 24, 2012

You should never assign a new value to a property by the property setter directly in the Executre method. This triggers new validation rules from inside the Execute method and makes the rules run recursively.

You should rather use context.AddOutValue to update property values.

In your case I would rather:

• inherit from CommonRules.CommonBusinessRule
• Add class constructor 
  • set CanRunAsAffectedProperty = false to make the rule run only for the property that was changed.
  • Add all properties to AffectedProperties list (makes rule engine to return these properties to caller and cann OnPropertyChanged to notify UI)
    
• call context.AddOutValue to update the Business object
  
• The property that was changed is available as PrimaryProperty property on the rule instance. 

gajit replied on Friday, August 24, 2012

Thanks Jonny - I'll look into that. is CanRunAsAffectedProperty just a tag of the property constructor?

JonnyBee replied on Friday, August 24, 2012

It is a property on rules that inherit from PropertyRule or CommonRules.CommonBusinessRule (that in turn inherits from PropertyRule).