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• Resources for popular domain models

  - by Songo

  I have come across many situations where I had to build a system for a library or a clinic or other popular domains. The thing is a domain model for a library was probably done 1000 times already with different level of details of course. Here is an example. Is there a popular website or community where one can find ready made domain models for popular systems? The whole purpose I'm trying to achieve is to quickly get a grasp of the domain I'm modeling and customize it to my needs. Re-inventing the wheel seems really absurd when the same system might have been modeled properly previously. Note I know Google might sound like the perfect source, but there is a repository out there that people can post there models, so that others can share them.

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• Whatchamacallit: You know how there are breadcrumbs and sliders and whatnot

  - by Richard

  What do you call it when a web site (especially corporate/retail) has a series of rows with thumbnails, each with a little caption/description beneath explaining some benefit or feature of a product or service. Is there a name for this? I'm building a theme that incorporates this kind of design and I was hoping there is some kind of shorthand for this design feature. If you don't know what I'm talking about, check out one of the links below. http://themeforest.net/item/revolution-minimalist-business-html-template/full_screen_preview/2295335 http://themes.two2twelve.com/preview?theme=freshserve

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• DDD and filtering

  - by tikhop

  I am developing an app in ddd maner. So I have a complex domain model. Suppose I have a Fare object and Airline. Each Airline should contain several or much more Fares. My UI should represent Model (only small part of complex model) as a list of Airline, when the user select the Airline, I must show the list of Fares. User can filtering the Fares (by travel time, cost, etc.). What is the appropriate place for filtering Fares and Airlines? I am assuming that I should do it in ViewModel. Like: My domain model has wrapped with Service Layer - UI works with ViewModel - ViewModel obtain data from Service Layer filtering it and create DTO objects for UI. Or I'm wrong?

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• Domain Models (PHP)

  - by Calum Bulmer

  I have been programming in PHP for several years and have, in the past, adopted methods of my own to handle data within my applications. I have built my own MVC, in the past, and have a reasonable understanding of OOP within php but I know my implementation needs some serious work. In the past I have used an is-a relationship between a model and a database table. I now know after doing some research that this is not really the best way forward. As far as I understand it I should create models that don't really care about the underlying database (or whatever storage mechanism is to be used) but only care about their actions and their data. From this I have established that I can create models of lets say for example a Person an this person object could have some Children (human children) that are also Person objects held in an array (with addPerson and removePerson methods, accepting a Person object). I could then create a PersonMapper that I could use to get a Person with a specific 'id', or to save a Person. This could then lookup the relationship data in a lookup table and create the associated child objects for the Person that has been requested (if there are any) and likewise save the data in the lookup table on the save command. This is now pushing the limits to my knowledge..... What if I wanted to model a building with different levels and different rooms within those levels? What if I wanted to place some items in those rooms? Would I create a class for building, level, room and item with the following structure. building can have 1 or many level objects held in an array level can have 1 or many room objects held in an array room can have 1 or many item objects held in an array and mappers for each class with higher level mappers using the child mappers to populate the arrays (either on request of the top level object or lazy load on request) This seems to tightly couple the different objects albeit in one direction (ie. a floor does not need to be in a building but a building can have levels) Is this the correct way to go about things? Within the view I am wanting to show a building with an option to select a level and then show the level with an option to select a room etc.. but I may also want to show a tree like structure of items in the building and what level and room they are in. I hope this makes sense. I am just struggling with the concept of nesting objects within each other when the general concept of oop seems to be to separate things. If someone can help it would be really useful. Many thanks

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• Algorithm to Solve Most of a Problem

  - by Mike G

  I need an Algorithm/Design Pattern that allows me to try to get the maximum number of rules followed. So I have a couple teams and I need to pair them with a referee and against each other into a round robin. There a rules on who can compete with who and who can judge who so I need to find the configuration that satisfies the most of these. Some rules are more important than others and are "worth more" when evaluating "what satisfies the most of them" There probably isn't a algorithm for this, but is there a design pattern that could help me maximize my chances of finding this configuration?

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• Exposing warnings\errors from data objects (that are also list returned)

  - by Oren Schwartz

  I'm exposing Data objects via service oriented assembly (which on future usages might become a WCF service). The data object is tree designed, as well as formed from allot of properties.Moreover, some services return one objects, others retrieve a list of them (thus disables throwing exceptions). I now want to expose data flow warnings and wondering what's the best way to do it having to things to consider: (1) seperation (2) ease of access. On the one hand, i want the UI team to be able to access a fields warnings (or errors) without having them mapping the field names to an external source but on the other hand, i don't want the warnings "hanged" on the object itself (as i don't see it a correct design). I tought of creating a new type of wrapper for each field, that'll expose events and they'll have to register the one's they care about (but totally not sure) I'll be happy to hear your thoughts. Could you please direct me to a respectful design pattern ? what dp will do best here ? Thank you very much!

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• How to avoid code duplication for a system which has logic that may change year wise?

  - by aravind

  What would be the way to design a system which has logic that may change year wise? There is an application which conducts online exams. There are five questions for a particular subject. The questions may (or may not) change year wise. As per my current design, the questions in database are stored year wise. There are some year specific code logic as well. In order to enable the application for another year, the year specific database records and code will be copied or duplicated. How to avoid this code duplication?

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• What should a domain object's validation cover?

  - by MarcoR88

  I'm trying to figure out how to do validation of domain objects that need external resources, such as data mappers/dao Firstly here's my code class User { const INVALID_ID = 1; const INVALID_NAME = 2; const INVALID_EMAIL = 4; int getID(); void setID(Int i); string getName(); void setName(String s); string getEmail(); void setEmail(String s); int getErrorsForInsert(); // returns a bitmask for INVALID_* constants int getErrorsForUpdate(); } My worries are about the uniqueness of the email, checking it would require the storage layer. Reading others' code seems that two solutions are equally accepted: both perform the unique validation in data mapper but some set an error state to the DO user.addError(User.INVALID_EMAIL) while others prefer to throw a totally different type of exception that covers only persistence, like: UserStorageException { const INVALID_EMAIL = 1; const INVALID_CITY = 2; } What are the pros and cons of these solutions?

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• DDD / Layers and legacy systems

  - by CSM

  I have to refactor a complex C# app (many dialogs, mixed logic and so on). There is a part managing the communication with special hardware equipments (sending commands and receive data via asynchronous c# callbacks). The code is "spaghetti" with mixed UI/Logic/Communication/etc and my task is to split the layers in a DDD sense. So, to which layer belongs a callback driver routine? The callbacks are creating "bubbles" in the system, up to the UI layer and because of this I cannot enforce the essential principle that any element of a layer depends only on other elements in the same layer or on elements of the layers "beneath" it. Thank you in advance.

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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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• Can the following Domain Entity contain logic for creating/deleting other entities?

  - by user702769

  a) As far as I understand it, in most cases Domain Model DM doesn't contain code for creating/deleting domain entities, but instead it is the job of layers ( ie service layer or UI layer ) on top of DM to create/delete domain entities? b) Domain entities are modelled after real world entities. Assuming particular real world entity being abstracted does have the functionality of creating/deleting other real world entities, then I assume the domain entity abstracting this real world entity could also contain logic for creating/deleting other entities? class RobotDestroyerCreator { ... void heavyThinking() { ... if(...) unitOfWork.registerDelete(robot); ... if(...) { var robotNew = new Robot(...); unitOfWork.registerNew(robotNew); { ... } } Thank you

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• Updating query results

  - by Francisco Garcia

  Within a DDD and CQRS context, a query result is displayed as table rows. Whenever new rows are inserted or deleted, their positions must be calculated by comparing the previous query result with the most recent one. This is needed to visualize with an animation new or deleted rows. The model of my view contains an array of the displayed query results. But I need a place to compare its contents against the latest query. Right now I consider my model view part of my application layer, but the comparison of two query result sets seems something that must be done within the domain layer. Which component should cache a query result and which one compare them? Are view models (and their cached contents) supposed to be in the application layer?

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• Where we should put validation for domain model

  - by adisembiring

  I still looking best practice for domain model validation. Is that good to put the validation in constructor of domain model ? my domain model validation example as follows: public class Order { private readonly List<OrderLine> _lineItems; public virtual Customer Customer { get; private set; } public virtual DateTime OrderDate { get; private set; } public virtual decimal OrderTotal { get; private set; } public Order (Customer customer) { if (customer == null) throw new ArgumentException("Customer name must be defined"); Customer = customer; OrderDate = DateTime.Now; _lineItems = new List<LineItem>(); } public void AddOderLine //.... public IEnumerable<OrderLine> AddOderLine { get {return _lineItems;} } } public class OrderLine { public virtual Order Order { get; set; } public virtual Product Product { get; set; } public virtual int Quantity { get; set; } public virtual decimal UnitPrice { get; set; } public OrderLine(Order order, int quantity, Product product) { if (order == null) throw new ArgumentException("Order name must be defined"); if (quantity <= 0) throw new ArgumentException("Quantity must be greater than zero"); if (product == null) throw new ArgumentException("Product name must be defined"); Order = order; Quantity = quantity; Product = product; } } Thanks for all of your suggestion.

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• Should this code/logic be included in Business Objects class or a separate class?

  - by aspdotnetuser

  I have created a small application which has a three tier architecture and I have business object classes to represent entities such as User, Orders, UserType etc. In these classes I have methods that are executed when the Constuctor method of, for example, User is called. These methods perform calculations and generate details that setup data for attributes that are part of each User object. Here is the structure for the project in Visual Studio: Here is some code from the business object class User.cs: Public Class User { public string Name { get; set; } public int RandomNumber { get; set; } etc public User { Name = GetName(); RandomNumber = GetRandomNumber(); } public string GetName() { .... return name; } public int GetRandomNumber() { ... return randomNumber; } } Should this logic be included in the Business Object classes or should it be included in a Utilities class of some kind? Or in the business rules?

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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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• Using packages (gems, eggs, etc.) to create decoupled architectures

  - by Juan Carlos Coto

  The main issue Seeing the good support most modern programming platforms have for package management (think gem, npm, pip, etc), does it make sense to design an application or system be composed of internally developed packages, so as to promote and create a loosely coupled architecture? Example An example of this would be to create packages for database access, as well as for authentication and other components of the system. These, of course, use external packages as well. Then, your system imports and uses these packages - instead of including their code within its own code base. Considerations To me, it seems that this would promote code decoupling and help maintainability, almost in a Web-based-vs.-desktop-application kind of way (updates are applied almost automatically, single code base for single functionality, etc.). Does this seem like a rational and sane design concept? Is this actually used as a standard way of structuring applications today? Thanks very much!

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• Avoiding bloated Domain Objects

  - by djcredo

  We're trying to move data from our bloated Service layer into our Domain layer using a DDD approach. We currently have a lot of business logic in our services, which is spread out all over the place and doesn't benefit from inheritance. We have a central Domain class which is the focus of most of our work - a Trade. The Trade object will know how to price itself, how to estimate risk, validate itself, etc. We can then replace conditionals with polymorphism. Eg: SimpleTrade will price itself one way, but ComplexTrade will price itself another. However, we are worried that this will bloat the Trade class(s). It really should be in charge of its own processing but the class size is going to increase exponentially as more features are added. So we have choices: Put processing logic in Trade class. Processing logic is now polymorphic based on the type of the trade, but Trade class is now has multiple responsibilites (pricing, risk, etc) and is large Put processing logic into other class such as TradePricingService. No longer polymorphic with the Trade inheritance tree, but classes are smaller and easier to test. What would be the suggested approach?

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• Domain Model and Querying

  - by Tyrsius

  I am new to DDD, having worked only in Transaction-Script apps with an anemic model, or just Big Balls of Mud, so please forgive any terminology I abuse. I am trying to understand the proper separation between the domain model and the repository. What is the proper way to construct a domain object that is coming from a database, assuming the (incredibly simplified) need to query for objects by status (returns enumerable), or by ID. Should a factory be building the objects, exposing methods for GetByStatus() and GetByID(), using a DIed repository? Should a repository be called directly, knowing how to build a domain model from the DTO? Should the domain model have a constructor for get by ID, using a DIed repoistory to load the initial state, using some other (?) method for the list? I am not really sure what the best way would be, and this question has an answer advocating each one (these are certainly mutuallu exclusive).

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• How do web-developers do web-design when freelancing?

  - by Gerald Blizz

  So I got my first job recently as junior web-developer. My company creates small/medium sites for wide variety of customers: autobusiness companies, weddign agencies, some sauna websites, etcetc, hope you get my point. They don't do big serious stuff like bank systems or really big systems, it's mostly small/medium-sized websites for startups/medium sized business. My main skills are PHP/MySQL, I also know HTML and a bit of CSS/JS/AJAX. I know that good web-developer must know some backend language (like PHP/Ruby/Python) AND HTML+CSS+JS+AJAX+JQuery combo. However, I was always wondering. In my company we have web-designer. In other serious organisations I often see the same stuff: web-developers who create business-logic and web-designers, who create design. As far as I know, after designers paint design of website they give it to developers either in PSD or sliced way, and developers put it together with logic, but design is NOT created by developers. Such separation seems very good for full-time job, but I am concerned with question how do freelance web-developers do websites? Do most of them just pay freelance designers to create design for them? Or do some people do both? Reason why I ask - I plan to start some freelancing in my free time after I get good at web-development. But I don't want to create websites with great business-logic but poor design. Neither I want to let someone else create a design for me. I like web-development very much and I am doing quite good, I like design aswell, even though I am a bit lost how to study it and get better at it. But I am scared that going in both directions won't let me become expert, it seems like two totally different jobs and getting really good in both seems very hard. But I really want to do both. What should I do? Thank you!

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• tdd is about design not verification what does it concretely mean?

  - by sigo

  I've been wondering about this. What do we exactly mean by design and verification. Should I just apply tdd to make sure my code is SOLID and not check is correct external behaviour ? Should I use Bdd for the correct behaviour part ? Where I get confused also is regarding TDD code katas, to me they looked like more about verification than design... shouldn't they be called bdd katas instead of tdd katas? I reckon that for example uncle bob bowling kata leads in the end to a simple and nice internal design but I felt that most of the process was more around vérification than design. Design seemed to be a side effect of testing incrementally the external behaviour. I didnt feel so much that we were focusing most of our efforts on design but more on vérification. While normally we are told the contrary, that in TDD, verification is a side effect, design is the main purpose. So my question is what should i focus exactly on when i do tdd: SOLID, external Api usability, what else...? And how can I do that without being focused on verification ? What do you guys focus your energy on when you are practicing TDD ?

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• "TDD is about design, not verification"; concretely, what does that mean?

  - by sigo

  I've been wondering about this. What do we exactly mean by design and verification. Should I just apply TDD to make sure my code is SOLID and not check if it's external behaviour is correct? Should I use BDD for verifying the behaviour is correct? Where I get confused also is regarding TDD code Katas, to me they looked like more about verification than design; shouldn't they be called BDD Katas instead of TDD Katas? I reckon that for example the Uncle Bob bowling Kata leads in the end to a simple and nice internal design but I felt that most of the process was centred more around verification than design. Design seemed to be a side effect of testing the external behaviour incrementally. I didn't feel so much that we were focusing most of our efforts on design but more on verification. While normally we are told the contrary, that in TDD, verification is a side effect, design is the main purpose. So my question is what should I focus on exactly, when I do TDD: SOLID, external API usability, or something else? And how can I do that without being focused on verification? What do you guys focus your energy on when you are practising TDD?

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• How to sketch out an event-driven system?

  - by Jordan

  I'm trying to design a system in Node.js (an attempt at solving one of my earlier problems, using Node's concurrency) but I'm running into trouble figuring out how to draw a plan of how the thing should operate. I'm getting very tripped up thinking in terms of callbacks instead of returned values. The flow isn't linear, and it's really boggling my ability to draft it. How does one draw out an operational flow for an event-driven system? I need something I can look at and say "Ok, yes, that's how it will work. I'll start it over here, and it will give me back these results over here." Pictures would be very helpful for this one. Thanks. Edit: I'm looking for something more granular than UML, specifically, something that will help me transition from a blocking and object-oriented programming structure, where I'm comfortable, to a non-blocking and event driven structure, where I'm unfamiliar.

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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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• How to design database for tests in online test application

  - by Kien Thanh

  I'm building an online test application, the purpose of app is, it can allow teacher create courses, topics of course, and questions (every question has mark), and they can create tests for students and students can do tests online. To create tests of any courses for students, first teacher need to create a test pattern for that course, test pattern actually is a general test includes the number of questions teacher want it has, then from that test pattern, teacher will generate number of tests corresponding with number of students will take tests of that course, and every test for student will has different number of questions, although the max mark of test in every test are the same. Example if teacher generate tests for two students, the max mark of test will be 20, like this: Student A take test with 20 questions, student B take test only has 10 questions, it means maybe every question in test of student A only has mark is 1, but questions in student B has mark is 2. So 20 = 10 x 2, sorry for my bad English but I don't know how to explain it better. I have designed tables for: - User (include students and teachers account) - Course - Topic - Question - Answer But I don't know how to define associations between user and test pattern, test, question. Currently I only can think these: Test pattern table: name, description, dateStart, dateFinish, numberOfMinutes, maxMarkOfTest Test table: test_pattern_id And when user (is Student) take tests, I think i will have one more table: Result: user_id, test_id, mark but I can't set up associations among test pattern and test and question. How to define associations?

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• Photoshop Retro Vintage Design Tutorials

  - by Aditi

  Gone are the days when designers only wanted to create high glossy web2.0 gradient rich website designs. Now a days designers are coming up with rugged, retro & vintage themes for their website designs. Colorful or subtle with that worn out look the website seems like a masterpiece. It is not hard to pick up on such Photoshop techniques to master the art of making themes that are retro & vibrant. We have complied a list of tutorials you would like to learn from..rest is in your hands & creativity. Photochrom Vintage Postcard effect Turn your high definition photos into vintage postcards and use them in your website concepts. Learn More Add Retro Look to your Images Give that 1970’s retro look to your images and web concepts. It’s a very easy process using either patterns, brushes, colors or gradients, layer modes and variable opacity. Learn More Brushed metal effect, Just like World War Airplanes texture This is one of a kind photoshop tutorial that teaches how to use  noise and blur filters to create a brushed metal effect unlike other gradient based effects, Also it covers a few layer styles to create airplane graphic. Learn More Transform a New Image into Illustration, Retro Poster Style With the help of this tutorial you can create brilliant poster style or illustrative images and concepts for your new website. This tutorial is superb example of image enhancement & creative use of blending options in photoshop. Learn More Retro Neon Style Text Tutorial Just like the old days, the rainbow neon curvy text format that can be seen on many posters etc, can now be made for your use on website. This tutorial gives you a easy step by step procedure. Learn More Retro Dotted Photo Tutorial Find how to make a dotted poster of your image, pure retro feel. Learn More

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