Duncan Edwards Jones - Professional Profile

Definitely the aggregate needs to control writing to the event stream but maybe there are scenarios where the event stream can be read without the aggregate?

(Hmm - philosophers hat needed)

In the end it seems best if it does - and also a public method for each event that the aggregate can handles so that it is easily mocked up..

VB.NET

'------------------------------------------------------------------------------
' <auto-generated>
'     This code was generated by a tool.
'     Runtime Version:4.0.30319.42000
'
'     Changes to this file may cause incorrect behavior and will be lost if
'     the code is regenerated.
' </auto-generated>
'------------------------------------------------------------------------------

Option Strict Off
Option Explicit On

Imports CQRSAzure
Imports CQRSAzure.Aggregation
Imports CQRSAzure.EventSourcing

Namespace Football_League.Game
    
    '''<summary>
    '''A unique game between two teams
    '''</summary>
    Partial Public Class Game
        Inherits Object
        Implements IGame
        
        Private _Key As System.Guid
        
        Private m_eventStream As IEventStream(Of IGame)
        
        '''<summary>
        '''Empty constructor for serialisation
        '''This should be removed if serialisation is not needed
        '''</summary>
        Sub New()
            MyBase.New
        End Sub
        
        '''<summary>
        '''Create an instance of the aggregate from its key identifier
        '''</summary>
        Sub New(ByVal Key_In As Object)
            MyBase.New
            _Key = Key_In
        End Sub
        
        '''<summary>
        '''Returns the unique identifier of this Game
        '''</summary>
        Public Function GetAggregateIdentifier() As String Implements IAggregationIdentifier.GetAggregateIdentifier
            Return _Key.ToString
        End Function
        
        Public Sub SetKey(ByVal Key_In As System.Guid) Implements CQRSAzure.EventSourcing.IAggregationIdentifier(Of System.Guid).SetKey
            _Key = Key_In
        End Sub
        
        Public Sub AddEvent(ByVal eventToAdd As IEvent(Of IGame)) Implements IEventStream(Of IGame).AddEvent
            m_eventStream.Add(eventToAdd)
        End Sub
        
        '''<summary>
        '''A game is to be played in the future
        '''</summary>
        Public Sub Scheduled(ByVal eventToAdd As IScheduled)
        End Sub
        
        '''<summary>
        '''The date of a fixture has changed
        '''</summary>
        Public Sub Rescheduled(ByVal eventToAdd As IRescheduled)
        End Sub
        
        '''<summary>
        '''The game has kicked off
        '''</summary>
        Public Sub Started(ByVal eventToAdd As IStarted)
        End Sub
    End Class
End Namespace

Identity groups need some way of evaluating if any given identity is in or out of the group based on the event stream of that entity.

This is somewhat similar to how a projection works but I think to avoid confusion I shall call this specific case of a projection a "classifier".

(I'm probably going to rely on the magic of inheritance to make the code underlying this and the code underlying a projection match)

Classifiers

A classifier is a special form of a projection which runs over the event stream of an aggregate and decides if it is "in" or "out" of the identity group as at any given point in time.

In the above example of the "accounts held by US citizens" identity group the classifier might run over events occurring to the aggregate identifier "account" and decide if the account is in or out of the group based on "account opened", "beneficial ownership changed" and any other similar events.

Have the very early cut of the code generation from the CQRS DSL designer working now...

XML

'------------------------------------------------------------------------------
' <auto-generated>
'     This code was generated by a tool.
'     Runtime Version:4.0.30319.42000
'
'     Changes to this file may cause incorrect behavior and will be lost if
'     the code is regenerated.
' </auto-generated>
'------------------------------------------------------------------------------

Option Strict Off
Option Explicit On

Imports CQRSAzure
Imports CQRSAzure.Aggregation
Imports CQRSAzure.EventSourcing

Namespace Football_League.Player.eventDefinition

    '''<summary>
    '''Player registered with the league
    '''</summary>
    '''<remarks>
    '''This will generate the player's unique regsitration id
    '''</remarks>
    Partial Public Class Registered
        Inherits Object
        Implements IRegistered

        #Region "Private members"
        Private _PreviousClub As Date

        Private _Amateur As Boolean

        Private _DateOfBirth As Date
        #End Region

        '''<summary>
        '''Empty constructor for serialisation
        '''This should be removed if serialisation is not needed
        '''</summary>
        Sub New()
            MyBase.New
        End Sub

        '''<summary>
        '''Create and populate a new instance of this class from the underlying interface
        '''</summary>
        '''<remarks>
        '''This should be called when the event is created from an event stream
        '''</remarks>
        Sub New(ByVal RegisteredInit As IRegistered)
            MyBase.New
            _PreviousClub = RegisteredInit.PreviousClub
            _Amateur = RegisteredInit.Amateur
            _DateOfBirth = RegisteredInit.DateOfBirth
        End Sub

        '''<summary>
        '''Create and populate a new instance of this class from the underlying properties
        '''</summary>
        '''<remarks>
        '''This should be called when the event is created from an event stream
        '''</remarks>
        Sub New(ByVal PreviousClub_In As Date, ByVal Amateur_In As Boolean, ByVal DateOfBirth_In As Date)
            MyBase.New
            _PreviousClub = PreviousClub_In
            _Amateur = Amateur_In
            _DateOfBirth = DateOfBirth_In
        End Sub

        '''<summary>
        '''Where did the player come from
        '''</summary>
        Public ReadOnly Property PreviousClub() As Date
            Get
                Return _PreviousClub
            End Get
        End Property

        '''<summary>
        '''Is the player registered as an amateur
        '''</summary>
        Public ReadOnly Property Amateur() As Boolean
            Get
                Return _Amateur
            End Get
        End Property

        '''<summary>
        '''Player's date of birth
        '''</summary>
        Public ReadOnly Property DateOfBirth() As Date
            Get
                Return _DateOfBirth
            End Get
        End Property
    End Class
End Namespace

There's a long way to go from here - but this is definitely heading in the right direction!

although - code generation does result in some ugly variable names Smile | :)

C#

'''<summary>
'''Create and populate a new instance of this class from the underlying properties
'''</summary>
'''<remarks>
'''This should be called when the event is created from an event stream
'''</remarks>
Sub New(ByVal Start_In As Date, ByVal Court_In As Integer, ByVal Umpire_In As String, ByVal Player_s__1_In As String, ByVal Player_s__2_In As String)
    MyBase.New
    _Start = Start_In
    _Court = Court_In
    _Umpire = Umpire_In
    _Player_s__1 = Player_s__1_In
    _Player_s__2 = Player_s__2_In
End Sub

More code generation - this time for factory methods...

VB

'''<summary>
'''Factory method to create an instance of this event
'''</summary>
'''<param name="Date Of Birth">
'''Date of the birth
'''</param>
'''<param name="Observations">
'''Observations relating to the calf at birth
'''</param>
'''<param name="Heiffer Identifier">
'''Herd number of the calf's heiffer
'''</param>
Shared Function Create(ByVal Date_Of_Birth_In As Date, 
                       ByVal Observations_In As String, 
                       ByVal Heiffer_Identifier_In As String) As IBorn
    Return New Born(Date_Of_Birth_In, Observations_In, Heiffer_Identifier_In)
End Function

And code generation for projections....

VB.NET

'------------------------------------------------------------------------------
' <auto-generated>
'     This code was generated by a tool.
'     Runtime Version:4.0.30319.42000
'
'     Changes to this file may cause incorrect behavior and will be lost if
'     the code is regenerated.
' </auto-generated>
'------------------------------------------------------------------------------

Option Strict Off
Option Explicit On

Imports CQRSAzure
Imports CQRSAzure.Aggregation
Imports CQRSAzure.EventSourcing
Imports Herd.Cow
Imports Herd.Cow.eventDefinition

Namespace Herd.Cow.projection
    
    Partial Public Class Location
        Inherits Object
        Implements ILocation
        
        #Region "Private members"
        Private _In_Shed As Boolean
        
        Private _Location As String
        #End Region
        
        '''<summary>
        '''Is the animal indoors
        '''</summary>
        Public ReadOnly Property In_Shed() As Boolean Implements ILocation.In_Shed
            Get
                Return _In_Shed
            End Get
        End Property
        
        '''<summary>
        '''The name of the location of the animal
        '''</summary>
        Public ReadOnly Property Location() As String Implements ILocation.Location
            Get
                Return _Location
            End Get
        End Property
        
        '''<summary>
        '''Animal was moved to a different field
        '''</summary>
        Public Overloads Sub HandleEvent(ByVal eventToHandle As IMoved_To_Field) Implements CQRSAzure.EventSourcing.IHandleEvent(Of IMoved_To_Field).HandleEvent
            'On Moved To Field, For In Shed, unset the flag 
            _In_Shed = False
            'The name of the field the animal was moved to
            _Location = eventToHandle.Moved_To
        End Sub

        '''<summary>
        '''Animal was moved to a shed
        '''</summary>
        Public Overloads Sub HandleEvent(ByVal eventToHandle As IMoved_To_Shed) Implements CQRSAzure.EventSourcing.IHandleEvent(Of IMoved_To_Shed).HandleEvent
            'Flag the animal as being in the shed
            _In_Shed = True
            'On Moved To Shed, For Location, set to the value Shed Name
            _Location = eventToHandle.Shed_Name
        End Sub
    End Class
End Namespace

For a query definition, two classes are created. The "Definition" class is in charge of specifying the model for the input parameters and return parameters (as would be used in the MVVM / MVC front end):-

VB.NET

Imports CQRSAzure
Imports CQRSAzure.Aggregation
Imports CQRSAzure.EventSourcing
Imports CQRSAzure.QueryDefinition
Imports Herd.Cow

'''<remarks>
'''This does not denote gender - we use farming terms (Heiffer/Bullock etc.) for that
'''</remarks>
Namespace Herd.Cow.queryDefinition
    
    '''<summary>
    '''Get the location of the herd as at the given point in time
    '''</summary>
    Partial Public Class Get_Herd_Location_Definition
        Inherits QueryDefinitionBase(Of IEnumerable(Of IGet_Herd_Location_Definition_Return))
        Implements IGet_Herd_Location_Definition
        
        '''<summary>
        '''The effective date to return the results for
        '''</summary>
        Private Property As_Of_Date() As Date Implements IGet_Herd_Location_Definition.As_Of_Date
            Get
                Return MyBase.GetParameterValue("As Of Date", 0)
            End Get
            Set
                MyBase.SetParameterValue("As Of Date", 0, Value)
            End Set
        End Property
    End Class
End Namespace

And the "Handler" does the actual work of populating the return data for a query:-

VB.NET

Option Strict Off
Option Explicit On

Imports CQRSAzure
Imports CQRSAzure.Aggregation
Imports CQRSAzure.EventSourcing
Imports CQRSAzure.QueryDefinition
Imports CQRSAzure.QueryHandler
Imports Herd.Cow

'''<remarks>
'''This does not denote gender - we use farming terms (Heiffer/Bullock etc.) for that
'''</remarks>
Namespace Herd.Cow.queryHandler
    
    '''<summary>
    '''Get the location of the herd as at the given point in time
    '''</summary>
    Partial Public Class Get_Herd_Location_Handler
        Inherits Object
        Implements IGet_Herd_Location_Handler
        
        '''<summary>
        '''Handle the query definition
        '''Get the location of the herd as at the given point in time
        '''</summary>
        '''<param name="qryToHandle">
        '''The instance of the query definition to handle and return data for
        '''</param>
        Public Function HandleQuery() As IEnumerable(Of IGet_Herd_Location_Definition_Return) Implements IGet_Herd_Location_Handler.HandleQuery
            Dim queryReturn As IEnumerable(Of IGet_Herd_Location_Definition_Return) = Nothing
            'TODO : Populate the query return value
            Return queryReturn
        End Function
    End Class
End Namespace

It turns out that code generation for "Classifiers" is the hardest part.. so far I have:-

VB.NET

Imports CQRSAzure.EventSourcing
Imports CQRSAzure.IdentifierGroup
Imports Football_League.Team

Namespace Football_League.Team.classifier
    
    '''<summary>
    '''Classifier to determine if a team is in the premier league
    '''</summary>
    Partial Public Class Is_Premier_League
        Inherits Object
        Implements IIs_Premier_League
        
        '''<summary>
        '''Empty constructor for serialisation
        '''This should be removed if serialisation is not needed
        '''</summary>
        Sub New()
            MyBase.New
        End Sub
        
        '''<summary>
        '''The team was relegated down from the division
        '''</summary>
        Private Overloads Function Evaluate(ByVal eventToEvaluate As IRelegated) As EvaluationResult 
           Implements CQRSAzure.IdentifierGroup.IClassifierEventHandler(Of IRelegated).Evaluate
            'On Relegated,  always set to Exclude
            Return
        End Function
        
        '''<summary>
        '''Team was promoted up to a new division
        '''</summary>
        Private Overloads Function Evaluate(ByVal eventToEvaluate As IPromoted) As EvaluationResult 
                Implements CQRSAzure.IdentifierGroup.IClassifierEventHandler(Of IPromoted).Evaluate
            'On Promoted, if New Division Equals Premier League set to Include, otherwise set to Exclude
        End Function
    End Class
End Namespace

...harder than it should be Frown | :-(

So the plan is for a visual tool with which you create your CQRS model and have it CodeGen the required classes for events, projections, queries and commands - and the required documentation (both as code comments and as HTML files for the business users)

Progress is slow but steady - the diagramming is basically there but with some rough edges (using the modelling SDK) and I have started on the code generation using CodeDOM.

I reckon I'm about a month away from a serviceable beta.

(All help gratefully received)

I can't believe the documentation for the Visual Studio Modelling SDK and the use of it for domain specific languages is so sparse as it is such a powerful feature.

Does everyone who ever works with it:
1) Give up after a certain time or
2) Decide to keep their hard won learning to themselves?

end-of-rant

* I will spend a lot of time trying to get Azure machine learning experiment set up to do automated stock price anomaly detection. (I will probably not succeed.)

* I will continue to bang away on the "CQRS is brilliant" drum - and maybe actually produce a few code samples.

* I will gain more from CodeProject than I contribute to it, but keep trying to equalise the balance.

Blood pressure is inversely correlated to oil pressure.

http://www.merrioncomputing.com/Programming/PrintingNetGuide1.htm

Probably too large to turn into an article here, although there is a significant overlap with the articles I have already uploaded.
All feedback welcomed.

'--8<------------------------
Ex Datis:
Duncan Jones

Free eBook: Printing - a .NET Developer's Guide (Part 1)

Hi Duncan,

I just downloaded your ebook "Printing – a .NET developers guide". First of all thank a lot for this very precious document, I could not find anything better and easier explained in a so short document! Congratulation!

I would really appreciate some help and opinion from you as you have experience on print spool monitoring.

I tried to send you an email from your homepage (www.merrioncomputing.com) but some errors on the pages prevented me to send the mail.

Is there a way to contact you? Would really appreciate to make some basics questions about printingQueues and so on. Could you kindly sent your email address to me or contact me? My address is ermeglio71@hotmail.com.

I really hope you can give me some input, would be really apreciated a lot!
thans so much in advance!
ermeglio

Try the website contact form again. Should be fixed

Otherwise Duncan@ followed by that domain name

'--8<------------------------
Ex Datis:
Duncan Jones

Free eBook: Printing - a .NET Developer's Guide (Part 1)

2001 posts in 6 years and 6 months.
Not a high rate by any means...