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• DevExpress XAF, Behavior Driven Development (BDD), Domain Driven Development (DDD) and more&ndash;Introduction

  - by Patrick Liekhus

  OK.  I admit it.  I have been horrible at this blogging thing.  However, I have made a commitment to get better at it so here goes.  I have many crazy ideas when it comes to coding and how to make my processes better and now is the time to get them down on paper and get your feedback.  Now, these ideas might not be nearly as wild and crazy as Charlie Sheen, but at least they help me get through my coding assignments. So let’s start by laying out the vision and objectives of this exercise.  I have been trying to come up with the best set of tools, tips and practices so I can get a small team to be as productive as possible without burning out my resources.  My thoughts tend to lean towards the coding practices first as this is what I have been doing for years.  However, as one looks at the process as a whole, we need to remember to keep the users in mind.  If we don’t have a user to accept our application, do we really have an application in the first place? I have been using a commercial framework from DevExpress called eXpress Application Framework (XAF) with their eXpress Persistent Objects (XPO) behind the scenes for a few years.  We have had tremendous success with it and even implemented a code generation layer to save us some time.  Now we want more!!! My goals here are to create a technical stack that employs as many UI’s as possible, while being true to the layers and documenting the process along the way.  I will continue to have a series of these posts that will walk through each step as I work on it.  Right now here is what I have planned: Defining the solution SCRUM/Agile Story Planning Overview of Architectural Plan Feature Driven Development Domain Driven Development Persistence Layer with XPO Windows UI with XAF/XPO Web UI with XAF/XPO OData Services Layer Windows Mobile UI Android UI iPhone UI Blackberry UI Excel UI Outlook UI Lessons Learned I will explain the solution that I plan to implement in the next post.  Thanks again and let me know what you think.

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• NDC 2010: Eric Evans Folding together DDD into Agile

  One of the most puzzling emails Eric have received was one claiming that his book really proved that up front design was important. In large this is a miss conception on how modeling happens. A tremendous amount of knowledge comes from actually implementing the software. You have the most insight at the end of the [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• NDC 2010: Eric Evans Folding together DDD into Agile

  One of the most puzzling emails Eric have received was one claiming that his book really proved that up front design was important. In large this is a miss conception on how modeling happens. A tremendous amount of knowledge comes from actually implementing the software. You have the most insight at the end of the [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Circular dependency and object creation when attempting DDD

  - by Matthew

  I have a domain where an Organization has People. Organization Entity public class Organization { private readonly List<Person> _people = new List<Person>(); public Person CreatePerson(string name) { var person = new Person(organization, name); _people.Add(person); return person; } public IEnumerable<Person> People { get { return _people; } } } Person Entity public class Person { public Person(Organization organization, string name) { if (organization == null) { throw new ArgumentNullException("organization"); } Organization = organization; Name = name; } public Organization { get; private set; } public Name { get; private set; } } The rule for this relationship is that a Person must belong to exactly one Organization. The invariants I want to guarantee are: A person must have an organization this is enforced via the Person's constuctor An organization must know of its people this is why the Organization has a CreatePerson method A person must belong to only one organization this is why the organization's people list is not publicly mutable (ignoring the casting to List, maybe ToEnumerable can enforce that, not too concerned about it though) What I want out of this is that if a person is created, that the organization knows about its creation. However, the problem with the model currently is that you are able to create a person without ever adding it to the organizations collection. Here's a failing unit-test to describe my problem [Test] public void AnOrganizationMustKnowOfItsPeople() { var organization = new Organization(); var person = new Person(organization, "Steve McQueen"); CollectionAssert.Contains(organization.People, person); } What is the most idiomatic way to enforce the invariants and the circular relationship?

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• Programming and Ubiquitous Language (DDD) in a non-English domain

  - by Sandor Drieënhuizen

  I know there are some questions already here that are closely related to this subject but none of them take Ubiquitous Language as the starting point so I think that justifies this question. For those who don't know: Ubiquitous Language is the concept of defining a (both spoken and written) language that is equally used across developers and domain experts to avoid inconsistencies and miscommunication due to translation problems and misunderstanding. You will see the same terminology show up in code, conversations between any team member, functional specs and whatnot. So, what I was wondering about is how to deal with Ubiquitous Language in non-English domains. Personally, I strongly favor writing programming code in English completely, including comments but ofcourse excluding constants and resources. However, in a non-English domain, I'm forced to make a decision either to: Write code reflecting the Ubiquitous Language in the natural language of the domain. Translate the Ubiquitous Language to English and stop communicating in the natural language of the domain. Define a table that defines how the Ubiquitous Language translates to English. Here are some of my thoughts based on these options: 1) I have a strong aversion against mixed-language code, that is coding using type/member/variable names etc. that are non-English. Most programming languages 'breathe' English to a large extent and most of the technical literature, design pattern names etc. are in English as well. Therefore, in most cases there's just no way of writing code entirely in a non-English language so you end up with mixed languages anyway. 2) This will force the domain experts to start thinking and talking in the English equivalent of the UL, something that will probably not come naturally to them and therefore hinders communication significantly. 3) In this case, the developers communicate with the domain experts in their native language while the developers communicate with each other in English and most importantly, they write code using the English translation of the UL. I'm sure I don't want to go for the first option and I think option 3 is much better than option 2. What do you think? Am I missing other options? UPDATE Today, about year later, having dealt with this issue on a daily basis, I have to say that option 3 has worked out pretty well for me. It wasn't as tedious as I initially feared and translating in real time while talking to the client wasn't a problem either. I also found the following advantages to be true, based on my experience. Translating the UL makes you pay more attention to defining the UL and even the domain itself, especially when you don't know how to translate a term and you have to start looking through dictionaries etc. This has even caused me to reconsider domain modeling decisions a few times. It helps you make your knowledge of the English language more profound. Obviously, your code is much more pleasant to look at instead of being a mind boggling obscenity.

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• Programming and Ubiquitous Language (DDD) in a non-English domain

  - by Sandor Drieënhuizen

  I know there are some questions already here that are closely related to this subject but none of them take Ubquitous Language as the starting point so I think that justifies this question. For those who don't know: Ubiquitous Language is the concept of defining a (both spoken and written) language that is equally used across developers and domain experts to avoid inconsistencies and miscommunication due to translation problems and misunderstanding. You will see the same terminology show up in code, conversations between any team member, functional specs and whatnot. So, what I was wondering about is how to deal with Ubiquitous Language in non-English domains. Personally, I strongly favor writing programming code in English completely, including comments but ofcourse excluding constants and resources. However, in a non-English domain, I'm forced to make a decision either to: Write code reflecting the Ubiquitous Language in the natural language of the domain. Translate the Ubiquitous Language to English and stop communicating in the natural language of the domain. Define a table that defines how the Ubiquitous Language translates to English. Here are some of my thoughts based on these options: 1) I have a strong aversion against mixed-language code, that is coding using type/member/variable names etc. that are non-English. Most programming languages 'breathe' English to a large extent and most of the technical literature, design pattern names etc. are in English as well. Therefore, in most cases there's just no way of writing code entirely in a non-English language so you end up with a mixed languages. 2) This will force the domain experts to start thinking and talking in the English equivalent of the UL, something that will probably not come naturally to them and therefore hinders communication significantly. 3) In this case, the developers communicate with the domain experts in their native language while the developers communicate with each other in English and most importantly, they write code using the English translation of the UL. I'm sure I don't want to go for the first option and I think option 3 is much better than option 2. What do you think? Am I missing other options?

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• Applying DDD principles in a RESTish web service

  - by Andy

  I am developing an RESTish web service. I think I got the idea of the difference between aggregation and composition. Aggregation does not enforce lifecycle/scope on the objects it references. Composition does enforce lifecycle/scope on the objects it contain/own. If I delete a composite object then all the objects it contain/own are deleted as well, while the deleting an aggregate root does not delete referenced objects. 1) If it is true that deleting aggregate roots does not necessary delete referenced objects, what sense does it make to not have a repository for the references objects? Or are aggregate roots as a term referring to what is known as composite object? 2) When you create an web service you will have multiple endpoints, in my case I have one entity Book and another named Comment. It does not make sense to leave the comments in my application if the book is deleted. Therefore, book is a composite object. I guess I should not have a repository for comments since that would break the enforcement of lifecycle and rules that the book class may have. However I have URL such as (examples only): GET /books/1/comments POST /books/1/comments Now, if I do not have a repository for comments, does that mean I have to load the book object and then return the referenced comments? Am I allowed to return a list of Comment entities from the BookRepository, does that make sense? The repository for Book may eventually become rather big with all sorts of methods. Am I allowed to write JPQL (JPA queries) that targets comments and not books inside the repository? What about pagination and filtering of comments. When adding a new comment triggered by the POST endpoint, do you need to load the book, add the comment to the book, and then update the whole book object? What I am currently doing is having a own CommentRepository, even though the comments are deleted with the book. I could need some direction on how to do it correct. Since you are exposing not only root objects in RESTish services I wonder how to handle this at the backend. I am using Hibernate and Spring.

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• How to model an address type in DDD?

  - by Songo

  I have an User entity that has a Set of Address where Address is a value object: class User{ ... private Set<Address> addresses; ... public setAddresses(Set<Address> addresses){ //set all addresses as a batch } ... } A User can have a home address and a work address, so I should have something that acts as a look up in the database: tbl_address_type ------------------------------------------------ | address_type_id | address_type | ------------------------------------------------ | 1 | work | ------------------------------------------------ | 2 | home | ------------------------------------------------ and correspondingly tbl_address ------------------------------------------------------------------------------------- | address_id | address_description |address_type_id| user_id | ------------------------------------------------------------------------------------- | 1 | 123 main street | 1 | 100 | ------------------------------------------------------------------------------------- | 2 | 456 another street | 1 | 100 | ------------------------------------------------------------------------------------- | 3 | 789 long street | 2 | 200 | ------------------------------------------------------------------------------------- | 4 | 023 short street | 2 | 200 | ------------------------------------------------------------------------------------- Should the address type be modeled as an Entity or Value type? and Why? Is it OK for the Address Value object to hold a reference to the Entity AdressType (in case it was modeled as an entity)? Is this something feasible using Hibernate/NHibernate? If a user can change his home address, should I expose a User.updateHomeAddress(Address homeAddress) function on the User entity itself? How can I enforce that the client passes a Home address and not a work address in this case? (a sample implementation is most welcomed) If I want to get the User's home address via User.getHomeAddress() function, must I load the whole addresses array then loop it and check each for its type till I found the correct type then return it? Is there a more efficient way than this?

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• DDD: service contains two repository

  - by tikhop

  Does it correct way to have two repository inside one service and will it be an application or domain service? Suppose I have a Passenger object that should contains Passport (government id) object. I am getting Passenger from PassengerRepository. PassengerRepository create request to server and obtain data (json) than parse received data and store inside repository. I have confused because I want to store Passport as Entity and put it to PassportRepository but all information about password contains inside json than i received above. I guess that I should create a PassengerService that will be include PassengerRepository and PassportRepository with several methods like removePassport, addPassport, getAllPassenger and etc. UPDATE: So I guess that the better way is represent Passport as VO and store all passports inside Passenger aggregate. However there is another question: Where I should put the methods (methods calls server api) for management passenger's passport. I think the better place is so within Passenger aggregate.

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• DDD/NHibernate Use of Aggregate root and impact on web design - ex. Editing children of aggregate ro

  - by pbrophy

  Hopefully, this fictitious example will illustrate my problem: Suppose you are writing a system which tracks complaints for a software product, as well as many other attributes about the product. In this case the SoftwareProduct is our aggregate root and Complaints are entities that only can exist as a child of the product. In other words, if the software product is removed from the system, so shall the complaints. In the system, there is a dashboard like web page which displays many different aspects of a single SoftwareProduct. One section in the dashboard, displays a list of Complaints in a grid like fashion, showing only some very high level information for each complaint. When an admin type user chooses one of these complaints, they are directed to an edit screen which allows them to edit the detail of a single Complaint. The question is: what is the best way for the edit screen to retrieve the single Complaint, so that it can be displayed for editing purposes? Keep in mind we have already established the SoftwareProduct as an aggregate root, therefore direct access to a Complaint should not be allowed. Also, the system is using NHibernate, so eager loading is an option, but my understanding is that even if a single Complaint is eager loaded via the SoftwareProduct, as soon as the Complaints collection is accessed the rest of the collection is loaded. So, how do you get the single Complaint through the SoftwareProduct without incurring the overhead of loading the entire Complaints collection?

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• DDD Modeling questions : student, classroom, seats and a favorite seat for a student.

  - by Erik Ashepa

  Hi, i'm not sure how to model this relationship... A classroom contains many seats, every student studies in a classroom and have a favorite seat within it. The way i see it, i have two aggregate roots: classroom and student, seats a are entities aggregatged by classroom... And for a student to have a fovorite seat, it must hold a reference to it (seat isn't an aggregate root). Any suggestions? Thanks in advance, Erik.

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• Is it bad practice for services to share a database in SOA?

  - by Paul T Davies

  I have recently been reading Hohpe and Woolf's Enterprise Integration Patterns, some of Thomas Erl's books on SOA and watching various videos and podcasts by Udi Dahan et al. on CQRS and Event Driven systems. Systems in my place of work suffer from high coupling. Although each system theoretically has its own database, there is a lot of joining between them. In practice this means there is one huge database that all systems use. For example, there is one table of customer data. Much of what I've read seems to suggest denormalising data so that each system uses only its database, and any updates to one system are propagated to all the others using messaging. I thought this was one of the ways of enforcing the boundaries in SOA - each service should have its own database, but then I read this: http://stackoverflow.com/questions/4019902/soa-joining-data-across-multiple-services and it suggests this is the wrong thing to do. Segregating the databases does seem like a good way of decoupling systems, but now I'm a bit confused. Is this a good route to take? Is it ever recommended that you should segregate a database on, say an SOA service, an DDD Bounded context, an application, etc?

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• Learning project Custom c# Cms [closed]

  - by user313378

  I want to start new project customCms, cause I think it's a good starting point to implement my collected knowledge from c#, ddd, nhibernate, mvc3, js. It will be great if I hear some guidlines from expirienced users here. I will use C# ASP.NET MVC3 razor view engine. Also I was thinking of NHibernate ORM, I dont know if using Nhibernate will cause performanse down. Initially MSSQL 2008 will be used, but using ORM layer cause that I can switch to some other db with no pain. I was thinking to create News entity which will have properties Id Name Created Updated IntroText Content Title Author ListPhotos Every input will be validated with untroub. java script on the view, and it will be validated on db level as well. Maybe it is best approach to create some interface which will be implemented by my cmsClient entity like NewsEntity. In this interface will be included everything it should be requested from my client in future. At least some stuff which are not included in entity right now, consumed data by rss feed, wcf, etc. So basically everything you think its good idea from documentating project, to coding. Everyone is welcomed to brainstorm for custom cms.

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• C# Domain-Driven Design Sample Released

  - by Artur Trosin

  In the post I want to declare that NDDD Sample application(s) is released and share the work with you. You can access it here: http://code.google.com/p/ndddsample. NDDDSample from functionality perspective matches DDDSample 1.1.0 which is based Java and on joint effort by Eric Evans' company Domain Language and the Swedish software consulting company Citerus. But because NDDDSample is based on .NET technologies those two implementations could not be matched directly. However concepts, practices, values, patterns, especially DDD, are cross-language and cross-platform :). Implementation of .NET version of the application was an interesting journey because now as .NET developer I better understand the differences positive and negative between these two platforms. Even there are those differences they can be overtaken, in many cases it was not so hard to match a java libs\framework with .NET during the implementation. Here is a list of technology stack: 1. .net 3.5 - framework 2. VS.NET 2008 - IDE 3. ASP.NET MVC2.0 - for administration and tracking UI 4. WCF - communication mechanism 5. NHibernate - ORM 6. Rhino Commons - Nhibernate session management, base classes for in memory unit tests 7. SqlLite - database 8. Windsor - inversion of control container 9. Windsor WCF facility - for better integration with NHibernate 10. MvcContrib - and in particular its Castle WindsorControllerFactory in order to enable IoC for controllers 11. WPF - for incident logging application 12. Moq - mocking lib used for unit tests 13. NUnit - unit testing framework 14. Log4net - logging framework 15. Cloud based on Azure SDK These are not the latest technologies, tools and libs for the moment but if there are someone thinks that it would be useful to migrate the sample to latest current technologies and versions please comment. Cloud version of the application is based on Azure emulated environment provided by the SDK, so it hasn't been tested on ‘real' Azure scenario (we just do not have access to it). Thanks to participants, Eugen Gorgan who was involved directly in development, Ruslan Rusu and Victor Lungu spend their free time to discuss .NET specific decisions, Eugen Navitaniuc helped with Java related questions. Also, big thank to Cornel Cretu, he designed a nice logo and helped with some browser incompatibility issues. Any review and feedback are welcome! Thank you, Artur Trosin

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• How can Domain driven design be combined with aspect oriented programming?

  - by anthares

  I'm doing research and one point I want to cover is "What is the relationship between Domain-driven Design and Aspect oriented programming?" I know that a main principle in DDD is separation of concerns and I understand that. What I'm not really certain is, whether aspects in AOP acts like "sub domains" in our domain in DDD. Are these two concepts, basically the same thing. I mean, If I develop an application following AOP and DDD, at the end of the day will it be true that "a sub domain" == "an aspect". I will also appreciate any other opinions what is the common between AOP and DDD.

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• How to split a string by ',' or '[|]' unless the ',' is in '{}'

  - by floyddotnet

  i search for a regex to split the following string: aaa[bbb,ccc[ddd,{eee:1,mmm:999}],nnn[0,3]] aaa[bbb,ccc[ddd,{eee:1, mmm:[123,555]}],nnn[0,3]] aaa[bbb, ccc[ddd, ddd],nnn[0,3]] aaa[bbb,ddd[0,3]] by '[' or ']' or ',' unless the ',' is in '{}'. As example: split 'aaa[bbb,ccc[ddd,' to aaa, bbb, ccc, ddd is allow but not {eee:1,mmm:999}. the result: aaa, bbb, ccc, ddd, {eee:1,mmm:999}, nnn, 0, 3 aaa, bbb, ccc, ddd, {eee:1, mmm:[123,555]}], nnn, 0, 3 aaa, bbb, ccc, ddd, ddd, nnn, 0, 3 aaa, bbb, ddd, 0, 3 i have read meany other questions but i cant modifie the regex's there are post to do this what i want. the target language for the expression is javascript.

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• Chester Devs Presentation and source code &ndash; &lsquo;Event Store - an introduction to a DSD for event sourcing and notifications&rsquo;

  - by Liam Westley

  Originally posted on: http://geekswithblogs.net/twickers/archive/2013/11/11/chester-devs-presentation-and-source-code-ndash-lsquoevent-store.aspxThank you everyone at Chester Devs Thanks to Fran Hoey and all the people from Chester Devs. It was a hard drive up and back but the enthusiasm of the audience, with some great questions does make it worthwhile. Presentation and source code My presentation, source code, Event Store runners and text files containing the various command line parameters used for curl is now available on GitHub; https://github.com/westleyl/ChesterDevs-EventStore. Don’t worry if you don’t have a GitHub account, you don’t need one, you can just click on the Download Zip button on the right hand menu to download all the files as a single ZIP file.  If all you want is the PowerPoint presentation, go to https://github.com/westleyl/ChesterDevs-EventStore/blob/master/Powerpoint/Huddle-EventStore.pptx, and click on the View Raw button. Downloading and installing Event Store and Tools Download Event Store http://download.geteventstore.com – I unzipped these files into C:\EventStore\v2.0.1 Download Curl from http://curl.haxx.se/download.html – I downloaded Win64 Generic (with SSL) and unzipped these files into C:\curl version 7.31.0 Running the tools I used in my presentation Demonstration 1 (running Event Store) You can use one of my Event Store runner command files to run the single node version of Event Store, using default ports of 2213 for HTTP and 1113  for TCP, and with a wildcard HTTP pattern.  Both take a single command line parameter to specify the location of the data and log files.  The runners assume the single node executable is located in C:\EventStore\v2.0.1, and will placed data files and logs beneath C:\EventStore\Data, i.e. RunEventStore.cmd TestData1 This will create data files in C:\EventStore\Data\TestData1\Data and log files in C:\EventStore\Data\TestData1\logs. If, when running Event Store you may see the following message, [03288,15,06:23:00.622] Failed to start http server Access is denied You will either need to run Event Store in an administrator console window, or you can use the netsh command to create a firewall permission to allow HTTP listening (this will need to be run, once, in an administrator console window), netsh http add urlacl url=http://*:2213/ user=liam You can always delete this later by running the delete; netsh http delete urlacl url=http://*:2213/ If you want to confirm that everything is running OK, open the management console in a browser by navigating to http://127.0.0.1:2213. If at any point you are asked for a user name and password use the default of ‘admin’/‘changeit’. Demonstration 2 (reading and adding data, curl) In my second demonstration I used curl directly from the console to read streams, write events and then read back those events. On GitHub I have included is a set of curl commands, CurlCommandLine.txt, and a sample data file, SampleData.json, to load an event into a DDDNorth3 stream. As there is not much data in the Event Store at this point I used the $stats-127.0.0.1:2113 which is a stream containing performance statistics for Event Store and is updated every 30 seconds (default). Demonstration 3 (projections) On GitHub I have included a sample projection, Projection-ByRoom.txt, which will create streams based on the room on which a session was held on the DDDNorth3 agenda. Browse to the management console, http://127.0.0.1:2213.  Click on Projections, New Projection, give it a name, Sessions-ByRoom, and copy in the JavaScript in the Projection-ByRoom.txt file.  Select Continuous, tick Emit Enabled and then click on Post. It should run immediately. You may by challenged for the administration login for the management console, if so use the default user name and password; 'admin'/'changeit'. Demonstration 4 (C# client) The final demonstration was the Visual Studio 2012 project using the Event Store client – referenced directly as C:\EventStore\v2.0.1\EventStore.ClientAPI.dll, although you can switch this to the latest Event Store client NuGet package. The source code provides a console app for viewing projections with the projection manager (HTTP connection), as well as containing a full set of data for the entire DDDNorth3 agenda.  It also deals with the strategy for reading newest events backwards to older events and ignoring older events that have been superseded. Resources Event Store home page: http://www.geteventstore.com/ Event Store source code on GitHub: https://github.com/eventstore/eventstore Event Store documentation on GitHub: https://github.com/eventstore/eventstore/wiki (includes index to @RobAshton’s blog series on Event Store at https://github.com/eventstore/eventstore/wiki#rob-ashton---projections-series) Event Store forum in Google Groups: https://groups.google.com/forum/?fromgroups#!forum/event-store TopShelf Windows service wrapper is available on github: https://gist.github.com/trbngr/5083266

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• Application layer vs domain layer?

  - by Louis Rhys

  I am reading Domain-Driven Design by Evans and I am at the part discussing the layered architecture. I just realized that application and domain layers are different and should be separate. In the project I am working on, they are kind of blended and I can't tell the difference until I read the book (and I can't say it's very clear to me now), really. My questions, since both of them concerns the logic of the application and are supposed to be clean of technical and presentation aspects, what are the advantages of drawing a boundary these two?

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• Running Objects – Associations and Relationships

  - by edurdias

  After the introduction to the Running Objects with the tutorial Movie Database in 2 Minutes (available here), I would like to demonstrate how Running Objects interprets the Associations where we will cover: Direct Association – A reference to another complex object. Aggregation – A collection of another complex object. For those coming with a database perspective, by demonstrating these associations we will also exemplify the underline relationships such as 1 to Many and Many to Many relationships...(read more)

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• Do ORMs enable the creation of rich domain models?

  - by Augusto

  After using Hibernate on most of my projects for about 8 years, I've landed on a company that discourages its use and wants applications to only interact with the DB through stored procedures. After doing this for a couple of weeks, I haven't been able to create a rich domain model of the application I'm starting to build, and the application just looks like a (horrible) transactional script. Some of the issues I've found are: Cannot navigate object graph as the stored procedures just load the minimum amount of data, which means that sometimes we have similar objects with different fields. One example is: we have a stored procedure to retrieve all the data from a customer, and another to retrieve account information plus a few fields from the customer. Lots of the logic ends up in helper classes, so the code becomes more structured (with entities used as old C structs). More boring scaffolding code, as there's no framework that extracts result sets from a stored procedure and puts it in an entity. My questions are: has anyone been in a similar situation and didn't agree with the store procedure approch? what did you do? Is there an actual benefit of using stored procedures? appart from the silly point of "no one can issue a drop table". Is there a way to create a rich domain using stored procedures? I know that there's the posibility of using AOP to inject DAOs/Repositories into entities to be able to navigate the object graph. I don't like this option as it's very close to voodoo.

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• Creating Multiple Queries for Running Objects

  - by edurdias

  Running Objects combines the power of LINQ with Metadata definition to let you leverage multiples perspectives of your queries of objects. By default, RO brings all the objects in natural order of insertion and including all the visible properties of your class. In this post, we will understand how the QueryAttribute class is structured and how to make use of it. The QueryAttribute class This class is the responsible to specify all the possible perspectives of a list of objects. In other words, is...(read more)

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• How to choose between using a Domain Event, or letting the application layer orchestrate everything

  - by Mr Happy

  I'm setting my first steps into domain driven design, bought the blue book and all, and I find myself seeing three ways to implement a certain solution. For the record: I'm not using CQRS or Event Sourcing. Let's say a user request comes into the application service layer. The business logic for that request is (for whatever reason) separated into a method on an entity, and a method on a domain service. How should I go about calling those methods? The options I have gathered so far are: Let the application service call both methods Use method injection/double dispatch to inject the domain service into the entity, letting the entity do it's thing and then let it call the method of the domain service (or the other way around, letting the domain service call the method on the entity) Raise a domain event in the entity method, a handler of which calls the domain service. (The kind of domain events I'm talking about are: http://www.udidahan.com/2009/06/14/domain-events-salvation/) I think these are all viable, but I'm unable to choose between them. I've been thinking about this a long time and I've come to a point where I no longer see the semantic differences between the three. Do you know of some guidelines when to use what?

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• Should an image be able to resize itself in OOP?

  - by ChocoDeveloper

  I'm writing an app that will have an Image entity, and I'm already having trouble deciding whose responsibility each task should be. First I have the Image class. It has a path, width, and other attributes. Then I created an ImageRepository class, for retrieving images with a single and tested method, eg: findAllImagesWithoutThumbnail(). But now I also need to be able to createThumbnail(). Who should deal with that? I was thinking about having an ImageManager class, which would be an app-specific class (there would also be a third party image manipulation reusable component of choice, I'm not reinventing the wheel). Or maybe it would be 0K to let the Image resize itself? Or let the ImageRepository and ImageManager be the same class? What do you think?

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• Designing a hierarchical structure with lots of reads and writes?

  - by JD01

  I am in the process of working on a video on demand system part of it involves the management of a hierarchical tree structure (think windows explorer) which allows users to upload videos, move folders around, create new folders etc. User action will be allowed depending on which permissions they have. In addition to managing the structure (creating folders and uploading videos), subscribers will be viewing content (read access). The number of reads will be significantly more than the writes. My question (and it is big one) is should I store the data in a database (for the writes) and also have some sort of cache which will be used for the reads? or do I use two databases? or is there a better solution? Also I will have to resolve concurrency issues which I think optimistic locking on the database will resolve. I have a fair bit about CQRS over the last few months but not sure if this is the way to go. Any ideas?

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• Domain Specific Languages (DSL) and Domain Driven Design (DDD)

  - by bovium

  What is the differences and similarities between Domain Specific Languages (DSL) and Domain Driven Design (DDD)?

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