gmane.comp.programming.domain-driven-design

Questions : Relation between SOA, Domain Service, Repositories and Entities

tiger_lu_hao — 2012-05-22T01:51:09

Recently I joined a new company which is a travel company, they have an old asp system. I have been asked to develop a .net application to replace the old asp system. which I come across try to use DDD. This is the first time I am implementing apps using DDD.

I have read the book of Jimmy Nilsson "Applying Domain Driven Design and Patterns". I also downloaded the sample C# program about the cargo tracking. It really confused me about the relation between application services (SOA ??), Domain Service (Services in Eric Evan[DDD]), repositories and entities. I have the following question to ask(hopefully you guys can help me because I don't have a person to ask these questions):

1. Should the entity knows about the repositories? To do CRUD operations?

2 What is the domain services, first i thought they should handle domain business logic and algorithm. But it seem that from Jimmy's book the domain service can do CRUD operations as well. And also Entities can refer it as well. 

3 if entities that know about

Calendar with recurring events

sebaszipp — 2012-05-21T13:35:30

Hi all, 

I know this has been discussed around two years ago but I am looking for a concrete solution with recurring events involving complex time rules: daily, weekly, monthly. MS Outlook has a great deductive UI that helps to understand those rules. It will take place in a shared calendar and high volume. As Vaughn said in that previous thread the queries are really complex and I don't find any solution that involves just a query. Having in mind that we store the recurring event (and not the occurrences because of performance reasons) I see a potential solution similar to the one described by Martin Fowler in its Recurring document and doing in memory calculations based on the time expressions of each event.

Any help is appreciated.

Thanks,
Sebastian



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The Economics of Reuse: DDD vs SOA

remyfannader — 2012-05-20T04:24:43

Is DDD bound to a "Silo" approach, as opposed to SOA's "Peer to Peer" philosophy.
http://caminao.wordpress.com/engineering/system-engineering-processes/reuse/



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The 4th Annual DDD eXchange // Join us on June 15th!

Skills — 2012-05-17T10:50:27

Skills Matter is pleased to announce the 4th DDD eXchange taking place on June 15th! The annual conference brings together leading experts with 125 practitioners and enthusiasts for an interactive, high energy event.  Join us to learn and share with the leading designers and developers in DDD. The conference will be led by Eric Evans who will be speaking on 'Strategic Design and Established Formalisms'. Other highlights include Greg Young on 'Functional Programming with DDD', and Hans Dockter on 'Gradle and the Domain Model.' Don't miss the DDD exchange this June 15th, a truly established date in the DDD calendar. Read the full programme here!

What: DDD eXchange 
When: 15th June 2012
Wherre: Skills Matter, 116-120 Goswell Road, London, EC1V 7DP
Twitter: #dddx
Full Programme and tickets: http://bit.ly/DDDX2012



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Defining Associations

savvas_andreas_moysidis — 2012-05-10T17:00:31

Hello All,

I wanted to ask the community about their thoughts regarding the preferred strategy on defining associations in a model.
In my understanding, if an Aggregate Root is being defined then any domain associations need to defined and accessed only from within the Aggregate Root, so that the invariant it is maintaining can be satisfied.

But what if the model component is an Entity and not an Aggregate Root and there is no invariant to be maintained would it make sense to define in the model any associations that may exist in the domain based solely on the argument that they are present in the domain?
It is very often the case that too many associations are defined upfront without us really being able to explain the benefit that those associations bring (apart from facilitating UI rendering).

Any thoughts?

Cheers,
Savvas



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Beyond Layers: DDD and Architectural Styles (Plural)

vvernon_shiftmethod — 2012-05-08T05:59:41

See you on June 11 < at > #DDD Denver for the discussion:

"Beyond Layers: DDD and Architectural Styles (Plural)"

http://www.meetup.com/ddd-denver/

Vaughn



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Creating and refactoring identity fields of Entities

İbrahim ESEN — 2012-04-29T11:07:07

We are learning DDD and evaluating its use for a system backed by a legacy system & datastore.

We have been using Anti-Corruption Layer, Bubble Context and Bounded Context without knowing about them, and this approach seems very practical to us.

But we are not certain and confident about identification methods and identity correlation. Legacy data store does not have primary keys, instead uses composite unique indexes to identify information.

We are currently creating our model as Value objects that should be Entities (wishing to add "Long id" field to every one), or we rarely use combination of attributes used in unique indexes as id field. It seems clear to us that Entity models should have id fields.

Here are my concrete questions:

  *   We want our shiny new Entities to have "Long id" fields theoretically. Is it OK not to add that field now since that gives us no value as the backend data store won't fill or understand that field?
  *   Is it OK in DDD way to store identification informat

The cases for reuse

remyfannader — 2012-04-30T11:20:35

How to deal with objects targeted by different domains.
http://caminao.wordpress.com/2012/04/09/cases4reuse/



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francais [1 Attachment]

Remy Fannader — 2012-04-24T09:17:06

DDD queries

Sbhachu — 2012-04-20T16:59:22

Hi all,

I'm building a new application and am new to DDD. I've been reading through some of the documentation and I've managed to model most of the domain model but I would like some advice about two queries:

1. I have two domain objects channel and program. I've modelled these both as entities as both can be accessed independantly. A channel can have a list of programs so I have put this as an attribute of channel. My query is how should I populate the program list. Is it OK for the getChannerById method in ChannelService to first get the channel information and then call the programService to get the list of programs for the channels e.g: 

Channel {
  String channelId 
  List <Program> programList
} 

Program {
  String programId { 
}

ChannelService {
   Channel getChannelById(String channelId)
}

ProgramService {   
   Program getProgramById(String programId)
   List <Program> getProgramsByChannelById(String channelId)   
}

2. I have a product domain object but some of its attributes (e.g. specifica

Need for Diagnostic Methods/Algorithms to Classify Domain Objects

Ali Çevik — 2012-04-19T21:17:18

Hello,

First of all, I am aware that building blocks are not the core value of
DDD, but only patterns to keep things clear. Yet I've found them very
useful in many situations. But I still have many doubts when it comes to
classify the domain objects. (as entities, value objects, services,
aggregate roots, ...)

I see people spending a lot of time making these decisions too. There is
some knowledge floating around with variety of different understandings and
this makes the process even more difficult.

I think it would be really helpful if DDD experts could come up with a
diagnostic method (or more formally, an algorithm) (a hierarchical one,
perhaps?) that would help us classify our objects. I know people have been
saying things like "if object has an identity, it is entity" etc. But most
of these statements are ambiguous and they make the situation even more
complex.

I think what we need is a clear method, that consists of some diagnostic
steps to help us, something like:

Entity / Value Object Diagnosis:

DDD and Spring Security 3.1

tomasix — 2012-04-17T15:15:29

Hi, this is my first post in this group.

I'm building an app with Spring/Spring-MVC/Spring-Security 3.1. I'm  reading all that I can about DDD (bought the book). Also, I'm taking some lessons from http://dddsample.sourceforge.net/

The thing is, I have to implement a SS's CustomUserDetailsService (for custom authentication). The first obstacle is that I don't know in which layer I have to put this object. My first guess was the infrastructure layer but the thing is that the service knows about interfaces/objects from the domain layer and I thought domain layer had to use infrastructure layer and not the other way around. So I thought about the application layer, but that smells for other reasons.

Any thoughts? Someone with this kind of experience?

Thanks in advance.



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DDD in Flow3

johannes.steu — 2012-04-08T10:36:39

Hello,

i got a question about DDD in Flow3.
The Manual on http://flow3.typo3.org/documentation/guide/partii/modeling.html says in the section about Aggregates:

"If you want to display comments independently from their posts and blogs, you'd surely need a Comment Repository, too"

If i'd like to use a Comment Repository, will the model Comment still be inside the Aggregate?

Thanks,



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DDD and Acord within the insurance domain.

Alistair Bush — 2012-03-21T00:52:58

Hi Guys,

This isn't so much about DDD specifically but rather around how frameworks
such as Acord can be utilised with DDD applications.

My knowledge of Acord is very limited but from what I've seen so far it is
a Information Framework with lots of xml/edi schemas etc.  And it therefore
sits at the [web] service layer and can in part define interaction between
various systems.

I would be interested in hearing peoples thoughts and experiences on Acord
and DDD.

How applicable is the use of Acords "Business Glossary" [1] within DDD
projects.  My belief is that it is more of a context map than something
that can be used as the domain itself.  For me this is driven home by the
fact that Acord talks to data models as opposed to domain models.

I realise that this is a rather generic and open ended email,  but
hopefully something good comes out of it.  If you have experience with
other Frameworks like TMF SID (and DDD) I would also be very interested in
hearing about them.

The driver for this email came out of

Doubts when refactoring towards BCs

daniel_cadenas_nion — 2012-03-14T05:55:25

My first post!

I'm currently trying to apply DDD concepts in a Ruby on Rails application I'm working on that is growing fast. We are applying some of the concepts but we want to advance to the next level, identifying BCs and make a code refactor that reflects them explicitly by splitting the  model, and maybe at some point, upgrade them to autonomous applications. The main objective is increasing model clarity.

So I have some doubts when having this situation: 2 entities, each in a different bounded context, sharing the same identity.

1) Is it correct to say in this case that I have 2 entities? Or it's better to say that I have one entity with 2 different representations in each BC?

2) Their life cycles aren't necessarily the same, right?

For example, if I delete one of the entities in one of the bounded contexts it'd mean that its representation in that context no longer makes sense. 

3) I'm thinking that the smallest refactor I could make towards BCs is choosing some entity and splitting it in 2 to m

User interaction during a business process

moranlf — 2012-03-13T09:48:41

Greetings groupies

Consider the following business scenario of a data updating and versioning system, describing the process of loading a new file version into the versions catalog:
1. The user selects the CSCI id, a version number and browses for a file path.
2. The system checks the format of the specified file.
2.1 If the file's format is not compatible *the user is asked whether to upload the file anyway*.
2.1.1 If the user chooses not to upload the file, the process terminates.
2.1.2 If the user chooses to upload the file anyway, skip to 3.
3. The file is uploaded and saved in the catalog.

Two issues arise here:
1.  Checking the file format compatibility is done via an external service, implemented outside of the domain model. When a part of the process, which is defined by the domain experts as a single process has some logic which is executed on an external service, it cannot be modeled entirely in the domain model. This makes us implement some domain logic in an application layer service in order t

Looking for a Decent Way to Track Who Performed a Query on the Reporting Databas

2012-03-13T02:59:00

Hey all,

I'm looking for some ideas on the following potential scenario:
* User queries and gets a detail view for a Product through the Reporting Database
* The said User seeing that view needs to be persisted to the Product activity log view as an event
* The Product activity log view contains all Product related events raised from the Product aggregate.

From what I've been seeing, the Reporting Database is very thin and pure; it just lets you queries for read data. Where does it make sense to track that the User got a detail view and publish the event to the handler that writes to the Product activity log?

Regards,

Tony





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DDD and the database

alvl1973 — 2012-03-10T17:09:39

Hi,

I have been given the importunity to architect my first system.
The review from the three more experienced architects in my company has not gone well, they are not happy with my architecture.

The major problem is this. Within my application, the database belong exclusivity to the application. The application will be deployed to a very large number of clients. These clients don't care about how the data is stored or where, about the database and will never write any applications of themselves on the database. Even reporting is done within the realms of my application; however the reporting is done from a database which is separate from the OLTP database.

From the criteria above, I have thus come to the conclusion that the entities and value-objects in the Domain of the application is the same as the database. I thus use nhibernate, with the help of fluent hibernate, to map the domain objects to a database. It works out pretty well; the database is in 4th normal form, clean and very understandable. I un

I like my sherry DRY ... but what about my validations?

yves.reynhout — 2012-03-08T19:57:17

As promised, I'm starting a new thread here to discuss DRY and validation (which should be interpreted rather broadly).

Dan's most excellent articles about DRY are an excellent starting point to put things in perspective.
http://dearjunior.blogspot.com/2012/03/dry-is-about-ideas-not-text.html
http://dearjunior.blogspot.com/2012/03/dry-and-duplicated-code.html

So, the doctor asks: what's the problem?

Recently I've had some discussion with colleagues and some deep reflective thoughts with myself about keeping validation logic DRY. Validation comes in all shapes and sizes. There's the kind in the UI that enhances the UX, which mostly revolves around disabling things you can't do, notifying you as an end-user that the data you entered is invalid, or steering UI input controls with constraints such as maximum lengths, requiredness, between ranges, etc ... Notice how most of these things revolve around knowing metadata and the state "data" is in. Next to all that could be a service layer or command handler of s

Requirements capture

remyfannader — 2012-03-01T14:43:00

Using the Gof4 distinction between creational, structural, and
behavioral patterns for requirements capture.
http://caminao.wordpress.com/2012/03/01/requirements-strokes/
<http://caminao.wordpress.com/2012/03/01/requirements-strokes/>
Remy Fannader

We never talk about analysis any more

Greg Young — 2012-02-28T15:17:27

I was doing a run by posting of a game I like to play with domain experts.
Figured it might spark conversations on other games

http://goodenoughsoftware.net/2012/02/28/the-gibberish-game/