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• Sorting out POCO, Repository Pattern, Unit of Work, and ORM

  - by CoffeeAddict

  I'm reading a crapload on all these subjects: POCO Repository Pattern Unit of work Using an ORM mapper ok I see the basic definitions of each in books, etc. but I can't visualize this all together. Meaning an example structure (DL, BL, PL). So what, you have your DL objects that contain your CRUD methods, then your BL objects which are "mapped" using an ORM back to your DL objects? What about DTOs...they're your DL objects right? I'm confused. Can anyone really explain all this together or send me example code? I'm just trying to put this together. I am determining whether to go LINQ to SQL or EF 4 (not sure about NHibrernate yet). Just not getting the concepts as in physical layers and code layers here and what each type of object contains (just properties for DTOs, and CRUDs for your core DL classes that match the table fields???). I just need some guidance here. I'm reading Fowler's books and starting to read Evans but just not all there yet.

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• Where should configuration be placed?

  - by James P.

  I have an application structured as follows: dao domain main services utils I've made a class that reads the application configuration from an XML file. The question is where should it be placed? In the utilities package?

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• Comet with ASP.NET AsyncHttpHandlers

  - by Sumit

  I am implementing a comet using AsyncHttpHandlers in my current asp.net application. According to my implementation client initially sends Notification Hook request to server (with its user id) on AsyncHttpHandler, and on server side I maintain a Global (Application level) dictionary of userid(key) and IAynsResult (value). So when ever a request is received to send notification to a user I just pick the matching IAsyncResult from the Global Dictionary and send response to the client user. My concern is, is maintaing a Dictionary of Userid and IAsyncResult at Application level a good design? I feel it will put a lot of load on the server, at the time of high traffic. Is there any other way I can achieve the comet. or what will be the good design to achieve comet for high traffic scenarios.

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• Some good websites to learn about JavaScript and programming architecture?

  - by Jack Roscoe

  I'm not sure if 'architecture' is the correct term, but I've been looking for some articles online which talk about programming design and more about how best to use languages such as JavaScript in a code design sense rather than the actual syntax itself. I have found many websites but a lot seem to be very out dated, and I'm not sure what developments have taken place with JavaScript over the years so do not know how old is too old. If anybody could suggest some great websites, or maybe specific articles you think would be useful, that would be highly appreciated. I am a beginner programmer currently using JavaScript with XML and of course HTML & CSS, and I'm currently trying to get further into and learn more about web development.

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• What is the best practice in regards to building composite dtos off of an aggregate root with domain

  - by Chance

  I'm trying to figure out the best approach/practice for assembling a composite data transfer object off of an aggregate root and would love to hear people's thoughts on this. For example, lets say I have a root that has a few domain objects as children. I want to assemble a specific view dto, based on some business logic, that either has attributes or full dto's of it's objects. What I'm struggling with is trying to figure out where that assembly should happen. I can see it going on the domain object of the aggregate root as there is some business logic associated with it. The benefits of this approach from what I've deduced thus far is that it should reduce the inevitable business logic from bleeding outisde of the domain object. It also allows for private methods that take care of tasks that could become more complex from an external builder. The downsides being that the domain object becomes much more entrenched in the application's workflow and represents much more than just the domain object. It also could become very large in the scenario where you need multiple composite Dtos. Alternatively, I could also see it belonging to some form of transfer object assembler where there is a builder for each domain object. The domain objects would still be responsible for GetDto() and UpdateFromDto(dto). Outside of that, the builder would handle the construction and deconstruction of composite dtos. The downside is kind of mentioned above, where I fear this will easily lead to developers unfamiliar with DDD bleeding a ton of business logic into the assembler which is what I want to desperately avoid. Any thoughts would be greatly apperciated.

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• Where to handle fatal exceptions

  - by Stephen Swensen

  I am considering a design where all fatal exceptions will be handled using a custom UncaughtExceptionHandler in a Swing application. This will include unanticipated RuntimeExceptions but also custom exceptions which are thrown when critical resources are unavailable or otherwise fail (e.g. a settings file not found, or a server communication error). The UncaughtExceptionHandler will do different things depending on the specific custom exception (and one thing for all the unanticipated), but in all cases the application will show the user an error message and exit. The alternative would be to keep the UncaughtExceptionHandler for all unanticipated exceptions, but handle all other fatal scenarios close to their origin. Is the design I'm considering sound, or should I use the alternative?

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• ASP.Net 4.0 Database Created Pages

  - by Tyler

  I want to create asp.net 4.0 dynamic pages loaded from my MS SQL server. Basically, its a list of locations with informations. For example: Location1 would have the page www.site.com/location/location1.aspx Location44 would have the page www.site.com/location/location44.aspx I dont even know where to start with this, url writting maybe?

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• Database Abstraction & Factory Methods

  - by pws5068

  I'm interested in learning more about design practices in PHP for Database Abstraction & Factory methods. For background, my site is a common-interest social networking community currently in beta mode. Currently, I've started moving my old code for object retrieval to factory methods. However, I do feel like I'm limiting myself by keeping a lot of SQL table names and structure separated in each function/method. Questions: Is there a reason to use PEAR (or similar) if I dont anticipate switching databases? Can PEAR interface with the MySqli prepared statements I currently use? Will it help me separate table names from each method? (If no, what other design patterns might I want to research?) Will it slow down my site once I have a significantly large member base?

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• How should rules for Aggregate Roots be enforced?

  - by MylesRip

  While searching the web, I came across a list of rules from Eric Evans' book that should be enforced for aggregates: The root Entity has global identity and is ultimately responsible for checking invariants Root Entities have global identity. Entities inside the boundary have local identity, unique only within the Aggregate. Nothing outside the Aggregate boundary can hold a reference to anything inside, except to the root Entity. The root Entity can hand references to the internal Entities to other objects, but they can only use them transiently (within a single method or block). Only Aggregate Roots can be obtained directly with database queries. Everything else must be done through traversal. Objects within the Aggregate can hold references to other Aggregate roots. A delete operation must remove everything within the Aggregate boundary all at once When a change to any object within the Aggregate boundary is committed, all invariants of the whole Aggregate must be satisfied. This all seems fine in theory, but I don't see how these rules would be enforced in the real world. Take rule 3 for example. Once the root entity has given an exteral object a reference to an internal entity, what's to keep that external object from holding on to the reference beyond the single method or block? (If the enforcement of this is platform-specific, I would be interested in knowing how this would be enforced within a C#/.NET/NHibernate environment.)

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• Why should anonymous types cannot be passed around methods ?

  - by Vadi

  What is the design decision to lean towards not returning an anonymous types from a method?

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• Pagination in a Rich Domain Model

  - by user246790

  I use rich domain model in my app. The basic ideas were taken there. For example I have User and Comment entities. They are defined as following: <?php class Model_User extends Model_Abstract { public function getComments() { /** * @var Model_Mapper_Db_Comment */ $mapper = $this->getMapper(); $commentsBlob = $mapper->getUserComments($this->getId()); return new Model_Collection_Comments($commentsBlob); } } class Model_Mapper_Db_Comment extends Model_Mapper_Db_Abstract { const TABLE_NAME = 'comments'; protected $_mapperTableName = self::TABLE_NAME; public function getUserComments($user_id) { $commentsBlob = $this->_getTable()->fetchAllByUserId((int)$user_id); return $commentsBlob->toArray(); } } class Model_Comment extends Model_Abstract { } ?> Mapper's getUserComments function simply returns something like: return $this->getTable->fetchAllByUserId($user_id) which is array. fetchAllByUserId accepts $count and $offset params, but I don't know to pass them from my Controller to this function through model without rewriting all the model code. So the question is how can I organize pagination through model data (getComments). Is there a "beatiful" method to get comments from 5 to 10, not all, as getComments returns by default.

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• What question(s) does an object's behavior answer?

  - by Corwin

  Reading a book I have found the following statement: (Object) Behaviors answer either of two questions: What does this object do (for me)? or What can I do to this object? In the case of an orange, it doesn’t do a whole lot, but we can do things to it. One behavior is that it can be eaten. In my understanding of object behaviour the statement above is correct regarding the first question and is incorrect in case of the second. However, I often see classes with methods like Orange::eat(), and this makes me uncertain about my design skills. So I would like to ask is it a design mistake to give oranges a behaviour eat? (oranges and eat are used just for example)

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• Protecting sensitive entity data

  - by Andreas

  Hi, I'm looking for some advice on architecture for a client/server solution with some peculiarities. The client is a fairly thick one, leaving the server mostly to peristence, concurrency and infrastructure concerns. The server contains a number of entities which contain both sensitive and public information. Think for example that the entities are persons, assume that social security number and name are sensitive and age is publicly viewable. When starting the client, the user is presented with a number of entities, not disclosing any sensitive information. At any time the user can choose to log in and authenticate against the server, given the authentication is successful the user is granted access to the sensitive information. The client is hosting a domain model and I was thinking of implementing this as some kind of "lazy loading", making the first request instantiating the entities and later refreshing them with sensitive data. The entity getters would throw exceptions on sensitive information when they've not been disclosed, f.e.: class PersonImpl : PersonEntity { private bool undisclosed; public override string SocialSecurityNumber { get { if (undisclosed) throw new UndisclosedDataException(); return base.SocialSecurityNumber; } } } Another more friendly approach could be to have a value object indicating that the value is undisclosed. get { if (undisclosed) return undisclosedValue; return base.SocialSecurityNumber; } Some concerns: What if the user logs in and then out, the sensitive data has been loaded but must be disclosed once again. One could argue that this type of functionality belongs within the domain and not some infrastructural implementation(i.e. repository implementations). As always when dealing with a larger number of properties there's a risk that this type of functionality clutters the code Any insights or discussion is appreciated!

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• Is there a linear-time performance guarantee with using an Iterator?

  - by polygenelubricants

  If all that you're doing is a simple one-pass iteration (i.e. only hasNext() and next(), no remove()), are you guaranteed linear time performance and/or amortized constant cost per operation? Is this specified in the Iterator contract anywhere? Are there data structures/Java Collection which cannot be iterated in linear time? java.util.Scanner implements Iterator<String>. A Scanner is hardly a data structure (e.g. remove() makes absolutely no sense). Is this considered a design blunder? Is something like PrimeGenerator implements Iterator<Integer> considered bad design, or is this exactly what Iterator is for? (hasNext() always returns true, next() computes the next number on demand, remove() makes no sense). Similarly, would it have made sense for java.util.Random implements Iterator<Double>?

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• How would you organize this in asp.net mvc?

  - by chobo

  I have an asp.net mvc 2.0 application that contains Areas/Modules like calendar, admin, etc... There may be cases where more than one area needs to access the same Repo, so I am not sure where to put the Data Access Layers and Repositories. First Option: Should I create Data Access Layer files (Linq to SQL in my case) with their accompanying Repositories for each area, so each area only contains the Tables, and Repositories needed by those areas. The benefit is that everything needed to run that module is one place, so it is more encapsulated (in my mind anyway). The downside is that I may have duplicate queries, because other modules may use the same query. Second Option Or, would it be better to place the DAL and Repositories outside the Area's and treat them as Global? The advantage is I won't have any duplicate queries, but I may be loading a lot of unnecessary queries and DAL tables up for certain modules. It is also more work to reuse or modify these modules for future projects (though the chance of reusing them is slim to none :)) Which option makes more sense? If someone has a better way I'd love to hear it. Thanks!

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• Question about domain models & their visibility...

  - by Another SO User

  I was involved in an interesting debate about the visibility of domain models & was wondering if people here have any good guidance. Per my understanding of MDA, we need not expose the domain model throughout the application layers & tiers The reason being that any change to the domain model has an impact in the overall application The wise thing to do would be to expose light-weight object (DTO's) which are a small sub-set of the domain model to abstract the actual model On the flip side, any change to the domain model would mean changing various DTO's throughout the application for the change to be visible, while if we do expose the domain model, then the change is in a single location Hope to see some comments & thoughts about this. Appreciate all the help!

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• Multiple Rails forks with separate designs and layouts

  - by mettadore

  I have a Rails project that is basically a simple web app for a membership-based organization. We've open sourced the code on Github for the web app so that others can use it, but have a licensed design/layout that the original organization is going to use. This layout cannot be open sourced. I was wondering if others have run into the situation where you have an open-source Rails app with a non-OS design. My initial thought is to put app/views in .gitignore, and to have anyone forking the code add their own views directory, perhaps including an app/views_default directory with a web-app-theme layout or something else to get people running. Is this the best option (realizing that there are other files such as JavaScript, CSS, etc that come with the layout that must also be ignored). Does anyone have some good thoughts or pointers on this?

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• How have your coding values changed since graduating?

  - by Matt

  We all walked out of school with the stars in our eyes and little experience in "real-world" programming. How have your opinions on programming as a craft changed since you've gained more experience away from academia? I've become more and more about design a la McConnell : wide use of encapsulation, quality code that gives you warm fuzzy feelings when you read it, maintainability over execution performance, etc..., whereas many of my co-workers have followed a different path of fewer middlemen layers getting in the way, code that is right out in the open and easier to locate, even if harder to read, and performance-centric designs. What have you learned about the craft of software design which has changed the way you approach coding since leaving the academic world?

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• Define "Validation in the Model"

  - by sunwukung

  There have been a couple of discussions regarding the location of user input validation: http://stackoverflow.com/questions/659950/should-validation-be-done-in-form-objects-or-the-model http://stackoverflow.com/questions/134388/where-do-you-do-your-validation-model-controller-or-view These discussions were quite old, so I wanted to ask the question again to see if anyone had any fresh input. If not, I apologise in advance. If you come from the Validation in the Model camp - does Model mean OOP representation of data (i.e. Active Record/Data Mapper) as "Entity" (to borrow the DDD terminology) - in which case you would, I assume, want all Model classes to inherit common validation constraints. Or can these rules simply be part of a Service in the Model - i.e. a Validation service? For example, could you consider Zend_Form and it's validation classes part of the Model? The concept of a Domain Model does not appear to be limited to Entities, and so validation may not necessarily need to be confined to this Entities. It seems that you would require a lot of potentially superfluous handing of values and responses back and forth between forms and "Entities" - and in some instances you may not persist the data recieved from user input, or recieve it from user input at all.

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• How to face observable object containing an observable field

  - by iseek

  Hello, I need a hint concerning MVC and Observer-Pattern. For example a model contains the classes "Address" and "Person". The Address class contains the fields street:String, zipcode:String, location:String. Whereas the Person class contains the fields name:String, firstName:String, address:Address. My approach so far looks something like this: Both, Address and Person are observable. If one of their setters is being called, I validate whether the current value and new value differ. Only in this case an update event is fired. The event contains the source, the name of the changed field, the old and the new value. The class for the view contains text fields to display and edit the information of a person: name, firstname, street, zipcode, location. It knows the Person model and is an subscribed observer for the person. So it gets the update events from the person object. My questions concerns the address field from type Address in the person class, since an address is observable on its own. If the view gets an update event from person when a new address has been set, I can update all of the address related fields in the view. But what if a field of the address changes? Should the view also register for update events from the address? Any hints about common design approaches would be appreciated. Greetings.

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• How to handle injecting dependencies into rich domain models?

  - by Arne

  In a web server project with a rich domain model (application logic is in the model, not in the services) how do you handle injecting the dependencies into the model objects? What are your experiences? Do you use some form of AOP? Like Springs @Configurable annotation? Load time or build time weawing? Problems you encountered? Do you use manual injection? Then how do you handle different instantiation scenarios (creating of the objects through an library [like Hibernate], creating objects with "new" ...)? Or do you use some other way of injecting the dependencies?

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• How to add user customized data to database?

  - by CSharperWithJava

  I am trying to design a sqlite database that will store notes. Each of these notes will have common fields like title, due date, details, priority, and completed. In addition though, I would like to add data for more specialized notes like price for shopping list items and author/publisher data for books. I also want to have a few general purpose fields that users can fill with whatever text data they want. How can I design my database table in this case? I could just have a field for each piece of data for every note, but that would waste a lot of fields and I'd like to have other options and suggestions.

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• How can I handle all my errors/messages in one place on an Asp.Net page?

  - by Atomiton

  Hi all, I'm looking for some guidance here. On my site I put things in Web user controls. For example, I will have a NewsItem Control, an Article Control, a ContactForm control. These will appear in various places on my site. What I'm looking for is a way for these controls to pass messages up to the Page that they exist on. I don't want to tightly couple them, so I think I will have to do this with Events/Delegates. I'm a little unclear as to how I would implement this, though. A couple of examples: 1 A contact form is submitted. After it's submitted, instead of replacing itself with a "Your mail has been sent" which limits the placement of that message, I'd like to just notify the page that the control is on with a Status message and perhaps a suggested behaviour. So, a message would include the text to render as well as an enum like DisplayAs.Popup or DisplayAs.Success 2 An Article Control queries the database for an Article object. Database returns an Exception. Custom Exception is passed to the page along with the DisplayAs.Error enum. The page handles this error and displays it wherever the errors go. I'm trying to accomplish something similar to the ValidationSummary Control, except that I want the page to be able to display the messages as the enum feels fit. Again, I don't want to tightly bind or rely a control existing on the Page. I want the controls to raise these events, but the page can ignore them if it wants. Am I going about this the right way? I'd love a code sample just to get me started. I know this is a more involved question, so I'll wait longer before voting/choosing the answers.

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• conceptually different entities with a few similar properties should be stored in one table or more?

  - by Haghpanah

  Assume A and B are conceptually different entities that have a few similar properties and of course their own specific properties. In database design, should I put those two entities in one big aggregated table or two respectively designed tables. For instance, I have two types of payment; Online-payment and Manual-payment with following definition, TABLE [OnlinePayments] ( [ID] [uniqueidentifier], [UserID] [uniqueidentifier], [TrackingCode] [nvarchar](32), [ReferingCode] [nvarchar](32), [BankingAccID] [uniqueidentifier], [Status] [int], [Amount] [money], [Comments] [nvarchar](768), [CreatedAt] [datetime], [ShopingCartID] [uniqueidentifier], ) And TABLE [ManualPayments] ( [ID] [uniqueidentifier], [UserID] [uniqueidentifier], [BankingAccID] [uniqueidentifier], [BankingOrgID] [uniqueidentifier], [BranchName] [nvarchar](64), [BranchCode] [nvarchar](16), [Amount] [money], [SlipNumber] [nvarchar](64), [SlipImage] [image], [PaidAt] [datetime], [Comments] [nvarchar](768), [CreatedAt] [datetime], [IsApproved] [bit], [ApprovedByID] [uniqueidentifier], ) One of my friends told me that creating two distinct tables for such similar entities is not a well design method and they should be put in one single table for the sake of performance and ease of data manipulations. I’m now wondering what to do? What is the best practice in such a case?

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• Which entities should be Aggregate Roots?

  - by MylesRip

  If Book aggregates Chapter which in turn aggregates Page, then what should be the aggregate root? One possibility might be: Book is an aggregate root with Chapter as a leaf and Chapter is an aggregate with Page as a leaf. In this scenario, Chapter is a leaf in one aggregate and a root in another. Is this okay? Would it make sense in this scenario to have two repositories, one for Book and another for Chapter? If so, then couldn't the Chapter repository be used to circumvent the fact that access to Chapter should only happen via Book? What would be the best way to handle a situation like this?

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