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• Motivation for a service layer (instead of just copying dlls)?

  - by BornToCode

  I'm creating an application which has 2 different UIs so I'm making it with a service layer which I understood is appropriate for such scenario. However I found myself just creating web methods for every single method I have in the BL layer, so the services basically built from methods that looks like this: return customers_bl.Get_Customer_Prices(customer_id); I understood that a main point of the service layer is to prevent duplication of code so I asked myself - why not just import the BL.DLL (and the dal.dll) to the other UI, and whenever making a change re-copy the dlls, it might not be so 'neat', but still less hassle than one more layer? {I know something is wrong in my approach, I'm probably missing the importance of service layer, I'd like to get more motivation to create another layer, especially because as it is I found that many of my BL functions ALREADY looks like: return customers_dal.Get_Customer_Prices(cust_id) which led me to ask: was it really necessary to create the BL just because on several functions I actually have LOGIC inside the BL?} so I'm looking for more motivation to creating ONE MORE layer, I'm sure it's not just to make it more convenient that I won't have to re-copy the dlls on changes? Am I grasping it wrong? Any simple guidelines on how to design service layer (corresponding to all the BL layer functions or not? any simple example?) any enlightenment on the subject?

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• Writing generic code when your target is a C compiler

  - by enobayram

  I need to write some algorithms for a PIC micro controller. AFAIK, the official tools support either assembler or a subset of C. My goal is to write the algorithms in a generic and reusable way without losing any runtime or memory performance. And if possible, I would like to do this without increasing the development time much and compromising the readability and maintainability much either. What I mean by generic and reusable is that I don't want to commit to types, array sizes, number of bits in a bit field etc. All these specifications, IMHO, point to C++ templates, but there's no compiler for it for my target. C macro metaprogramming is another option, but, again my opinion, that greatly reduces readability and increases development time. I believe what I'm looking for is a decent C++ to C translator, but I'd like to hear anything else that satisfies the above requirements. Maybe a translator from another high-level language to C that produces very efficient code, maybe something else. Please note that I have nothing against C, I just wish templates were available in it.

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• What is the good way of sharing specific data between ViewModels

  - by voroninp

  We have IAppContext which is injected into ViewModel. This service contains shared data: global filters and other application wide properties. But there are cases when data is very specific. For example one VM implements Master and the second one - Details of selected tree item. Thus DetailsVm must know about the selected item and its changes. We can store this information either in IAppContext or inside each concerned VM. In both cases update notifications are sent via Messenger. I see pros and cons for any of the approaches and can not decide which one is better. 1st: + explicitly exposed shared proerties, easy to follow dependencies - IAppContxt becomes cluttered with very specific data. 2nd: the exact opposite of the first and more memory load due to data duplication. May be someone can offer design alternatives or tell that one of the variants is objectively superior to the other cause I miss something important?

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• Implenting ActiveRecord with inheritance?

  - by King

  I recently converted an old application that was using XML files as the data store to use SQL instead. To avoid a lot of changes I basically created ActiveRecord style classes that inherited from the original business objects. For example SomeClassRecord :SomeClass //ID Property //Save method I then used this new class in place of the other one, because of polymorphism I didn't need to change any methods that took SomeClass as a parameter. Would this be considered 'Bad'? What would be a better alternative?

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• Is "convention over configuration" not violating basic programming principles?

  - by Geerten

  I was looking at the WPF MVVM framework Caliburn.Micro and read that a lot of standard things are based on naming conventions. For example, automatic binding of properties in the View to properties in the ViewModel. Although this seems to be convenient (removes some boilerplate code), my first instinct reaction is that it isn't completely obvious to a new programmer that will read this code. In other words, the functionality of the application is not completely explained by its own code, but also by the documentation of the framework. EDIT: So this approach is called convention over configuration. Since I could not find any questions concerning this, I altered my question: My question is: Is convention over configuration a correct way of simplifying things, or is it violating some programming principles (and if so, which ones)?

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• Writing a spell checker similar to "did you mean"

  - by user888734

  I'm hoping to write a spellchecker for search queries in a web application - not unlike Google's "Did you mean?" The algorithm will be loosely based on this: http://catalog.ldc.upenn.edu/LDC2006T13 In short, it generates correction candidates and scores them on how often they appear (along with adjacent words in the search query) in an enormous dataset of known n-grams - Google Web 1T - which contains well over 1 billion 5-grams. I'm not using the Web 1T dataset, but building my n-gram sets from my own documents - about 200k docs, and I'm estimating tens or hundreds of millions of n-grams will be generated. This kind of process is pushing the limits of my understanding of basic computing performance - can I simply load my n-grams into memory in a hashtable or dictionary when the app starts? Is the only limiting factor the amount of memory on the machine? Or am I barking up the wrong tree? Perhaps putting all my n-grams in a graph database with some sort of tree query optimisation? Could that ever be fast enough?

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• Help with MVC design pattern?

  - by user3681240

  I am trying to build a java program for user login but I am not sure if my MVC design is accurate. I have the following classes: LoginControl - servlet LoginBean - data holder java class with private variables getters and setters LoginDAO - concrete java class where I am running my SQL queries and doing rest of the logical work. Connection class - java class just to connect to the database view - jsp to display the results html - used for form Is this how you design a java program based on MVC design pattern? Please provide some suggestions?

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• Guidelines or Design pattern to develop configurable software

  - by Rumit Parakhiya

  I want to develop an application which would have it's own framework, using which developer can implement functionality very easily. Developer shouldn't have to code for each and every page or report. But, he can do it very easily by just configuring it using the framework provided. Some nice examples of it is SAP and Tally. They have got their own framework, using which anybody having knowledge of it can customize or extend functionality of the product. But, as I am beginner in this direction, I don't have any idea about where to start. Can anybody point me to some design pattern which I can follow or some similar open source software which I can refer?

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• Structuring Access Control In Hierarchical Object Graph

  - by SB2055

  I have a Folder entity that can be Moderated by users. Folders can contain other folders. So I may have a structure like this: Folder 1 Folder 2 Folder 3 Folder 4 I have to decide how to implement Moderation for this entity. I've come up with two options: Option 1 When the user is given moderation privileges to Folder 1, define a moderator relationship between Folder 1 and User 1. No other relationships are added to the db. To determine if the user can moderate Folder 3, I check and see if User 1 is the moderator of any parent folders. This seems to alleviate some of the complexity of handling updates / moved entities / additions under Folder 1 after the relationship has been defined, and reverting the relationship means I only have to deal with one entity. Option 2 When the user is given moderation privileges to Folder 1, define a new relationship between User 1 and Folder 1, and all child entities down to the grandest of grandchildren when the relationship is created, and if it's ever removed, iterate back down the graph to remove the relationship. If I add something under Folder 2 after this relationship has been made, I just copy all Moderators into the new Entity. But when I need to show only the top-level Folders that a user is Moderating, I need to query all folders that have a parent folder that the user does not moderate, as opposed to option 1, where I just query any items that the user is moderating. Thoughts I think it comes down to determining if users will be querying for all parent items more than they'll be querying child items... if so, then option 1 seems better. But I'm not sure. Is either approach better than the other? Why? Or is there another approach that's better than both? I'm using Entity Framework in case it matters.

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• writing an autopilot for a 2d game with newtonian physics

  - by Jargo

  The subject says it all. I am making a 2d space game with newtonian physics and I need pointers on how to write an autopilot for it. The requirements are best explained by an example. There is a target object which has speed- and position-vectors and there a spaceship that is controlled by the autopilot. This spaceship also have speed, position and maximum acceleration. The autopilot needs to control the ship that it either collides with the target, Or intercepts the target so that the ship has matching speed and position with the target. Could someone give me some pointers how to achieve this behavior or perhaps even an ready implementation? I am sure someone has written something like this before and there is no point in reinventing the wheel.

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• Pattern for loading and handling resources

  - by Enoon

  Many times there is the need to load external resources into the program, may they be graphics, audio samples or text strings. Is there a patten for handling the loading and the handling of such resources? For example: should I have a class that loads all the data and then call it everytime I need the data? As in: GraphicsHandler.instance().loadAllData() ...//and then later: draw(x,y, GraphicsHandler.instance().getData(WATER_IMAGE)) //or maybe draw(x,y, GraphicsHandler.instance().WATER_IMAGE) Or should I assign each resource to the class where it belongs? As in (for example, in a game): Graphics g = GraphicsLoader.load(CHAR01); Character c = new Character(..., g); ... c.draw(); Generally speaking which of these two is the more robust solution? GraphicsHandler.instance().getData(WATER_IMAGE) //or GraphicsHandler.instance().WATER_IMAGE //a constant reference

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• What Design Pattern is separating transform converters

  - by RevMoon

  For converting a Java object model into XML I am using the following design: For different types of objects (e.g. primitive types, collections, null, etc.) I define each its own converter, which acts appropriate with respect to the given type. This way it can easily extended without adding code to a huge if-else-then construct. The converters are chosen by a method which tests whether the object is convertable at all and by using a priority ordering. The priority ordering is important so let's say a List is not converted by the POJO converter, even though it is convertable as such it would be more appropriate to use the collection converter. What design pattern is that? I can only think of a similarity to the command pattern.

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• Layering Design Pattern in Java clean code style

  - by zeraDev

  As a Java developer, I am developing trying to use the clean code rules. But in my team we are facing a concrete problem: We have a business layer offering a service called "createObject", this service makes a lot of operation which can result to problem. E.g: parentObjectDontExist, objectAlreadyExist, dontHaveAuthorizationToCreate, operationFailed... and we want the UI using this service to display different information messages depending which error occurred. In old java dev, we should have create all signed exception type and throw it in createObject. As Clean code says, it is forbidden to use Exception for business logic AND signed exceptions are evil... Why not...But i don't know how to solved this problem and i don't want to use return code. How do you do? Thanks for youre experience return.

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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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• Dynamic Components

  - by Alex

  I am attempting to design a component-based architecture that allows Components to be dynamically enabled and disabled, much like the system employed by Unity3D. For example, all Components are implicitly enabled by default; however, if one desires to halt execution of code for a particular Component, one can disable it. Naively, I want to have a boolean flag in Component (which is an abstract class), and somehow serialize all method calls into strings, so that some sort of ComponentManager can check if a given Component is enabled/disabled before processing a method call on it. However, this is a pretty bad solution. I feel like I should employ some variation of the state paradigm, but I have yet to make progress. Any help would be greatly appreciated,

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• Entity and pattern validation vs DB constraint

  - by Joerg

  When it comes to performance: What is the better way to validate the user input? If you think about a phone number and you only want numbers in the database, but it could begin with a 0, so you will use varchar: Is it better to check it via the entity model like this: @Size(min = 10, max = 12) @Digits(fraction = 0, integer = 12) @Column(name = "phone_number") private String phoneNumber; Or is it better to use on the database side a CHECK (and no checking in the entity model) for the same feature?

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• Android design advice - services & broadcast receivers

  - by basudz

  I'm in the process of learning the Android SDK and creating some projects to get a grasp on the system. The current project I'm working with works just fine but I'd like to get some advice about other ways I can go about designing it. Here's what it needs to do. When a text message is received from a specific number, it should fire off a toast message that repeats at a certain interval for a specific duration. To make this work, I created an SMS BroadcastReceiver and checked the incoming messages for the number I'm looking for. If found, an IntentService would be started that would pull out the interval and duration from saved shared prefs. The IntentService would then fire off a broadcast. The BroadcastReceiver for this would catch it and use the AlarmManager to handle the toast message repetitions. This all works just fine, but I'm wondering if there's a cleaner or more efficient way of going about doing this? Any suggestions or advice?

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• How should I implement the repository pattern for complex object models?

  - by Eric Falsken

  Our data model has almost 200 classes that can be separated out into about a dozen functional areas. It would have been nice to use domains, but the separation isn't that clean and we can't change it. We're redesigning our DAL to use Entity Framework and most of the recommendations that I've seen suggest using a Repository pattern. However, none of the samples really deal with complex object models. Some implementations that I've found suggest the use of a repository-per-entity. This seems ridiculous and un-maintainable for large, complex models. Is it really necessary to create a UnitOfWork for each operation, and a Repository for each entity? I could end up with thousands of classes. I know this is unreasonable, but I've found very little guidance implementing Repository, Unit Of Work, and Entity Framework over complex models and realistic business applications.

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• What OO Design to use ( is there a Design Pattern )?

  - by Blundell

  I have two objects that represent a 'Bar/Club' ( a place where you drink/socialise). In one scenario I need the bar name, address, distance, slogon In another scenario I need the bar name, address, website url, logo So I've got two objects representing the same thing but with different fields. I like to use immutable objects, so all the fields are set from the constructor. One option is to have two constructors and null the other fields i.e: class Bar { private final String name; private final Distance distance; private final Url url; public Bar(String name, Distance distance){ this.name = name; this.distance = distance; this.url = null; } public Bar(String name, Url url){ this.name = name; this.distance = null; this.url = url; } // getters } I don't like this as you would have to null check when you use the getters In my real example the first scenario has 3 fields and the second scenario has about 10, so it would be a real pain having two constructors, the amount of fields I would have to declare null and then when the object are in use you wouldn't know which Bar you where using and so what fields would be null and what wouldn't. What other options do I have? Two classes called BarPreview and Bar? Some type of inheritance / interface? Something else that is awesome?

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• Moving from mock to real objects?

  - by jjchiw

  I'm like doing TDD so I started everything mocking objects, creating interface, stubbing, great. The design seems to work, now I'll implement the stuff, a lot of the code used in the stubs are going to be reused in my real implementation yay! Now should I duplicate the tests to use the real object implementation (but keeping the mocks object of the sensitive stuff like Database and "services" that are out of my context (http calls, etc...)) Or just change the mocks and stubs of the actual tests to use the real objects....... So the question is that, keep two tests or replace the stubs, mocks? And after that, I should keep designing with the mocks, stubs or just go with real objects? (Just making myself clear I'll keep the mock object of the sensitive stuff like database and services that are out of my context, in both situations.)

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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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• Writing and Understanding code

  - by Kitex

  I can write code. I can read code but I can't implement good code. How to develop deep understanding of any framework or stuff that we are working on? Is it looking into documentation and working on it? I have seen in this form that people that have great understanding of things they are working on. How is this possible? How to not scrape on the surface only? How to manage time vs learning vs productivity?

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• What are the best practices to use NHiberante sessions in asp.net (mvc/web api) ?

  - by mrt181

  I have the following setup in my project: public class WebApiApplication : System.Web.HttpApplication { public static ISessionFactory SessionFactory { get; private set; } public WebApiApplication() { this.BeginRequest += delegate { var session = SessionFactory.OpenSession(); CurrentSessionContext.Bind(session); }; this.EndRequest += delegate { var session = SessionFactory.GetCurrentSession(); if (session == null) { return; } session = CurrentSessionContext.Unbind(SessionFactory); session.Dispose(); }; } protected void Application_Start() { AreaRegistration.RegisterAllAreas(); FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters); RouteConfig.RegisterRoutes(RouteTable.Routes); BundleConfig.RegisterBundles(BundleTable.Bundles); var assembly = Assembly.GetCallingAssembly(); SessionFactory = new NHibernateHelper(assembly, Server.MapPath("/")).SessionFactory; } } public class PositionsController : ApiController { private readonly ISession session; public PositionsController() { this.session = WebApiApplication.SessionFactory.GetCurrentSession(); } public IEnumerable<Position> Get() { var result = this.session.Query<Position>().Cacheable().ToList(); if (!result.Any()) { throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.NotFound)); } return result; } public HttpResponseMessage Post(PositionDataTransfer dto) { //TODO: Map dto to model IEnumerable<Position> positions = null; using (var transaction = this.session.BeginTransaction()) { this.session.SaveOrUpdate(positions); try { transaction.Commit(); } catch (StaleObjectStateException) { if (transaction != null && transaction.IsActive) { transaction.Rollback(); } } } var response = this.Request.CreateResponse(HttpStatusCode.Created, dto); response.Headers.Location = new Uri(this.Request.RequestUri.AbsoluteUri + "/" + dto.Name); return response; } public void Put(int id, string value) { //TODO: Implement PUT throw new NotImplementedException(); } public void Delete(int id) { //TODO: Implement DELETE throw new NotImplementedException(); } } I am not sure if this is the recommended way to insert the session into the controller. I was thinking about using DI but i am not sure how to inject the session that is opened and binded in the BeginRequest delegate into the Controllers constructor to get this public PositionsController(ISession session) { this.session = session; } Question: What is the recommended way to use NHiberante sessions in asp.net mvc/web api ?

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• How should I structure the implementation of turn-based board game rules?

  - by Setzer22

  I'm trying to create a turn-based strategy game on a tilemap. I'm using design by component so far, but I can't find a nice way to fit components into the part I want to ask. I'm struggling with the "game rules" logic. That is, the code that displays the menu, allows the player to select units, and command them, then tells the unit game objects what to do given the player input. The best way I could thing of handling this was using a big state machine, so everything that could be done in a "turn" is handled by this state machine, and the update code of this state machine does different things depending on the state. However, this approach leads to a large amount of code (anything not model-related) going into a big class. Of course I can subdivide this big class into more classes, but it doesn't feel modular and upgradable enough. I'd like to know of better systems to handle this in order to be able to upgrade the game with new rules without having a monstruous if/else chain (or switch / case, for that matter). Any ideas? What specific design pattern other than MVC should I be using?

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• Web programming, standard way to deal with a response that takes time to complete

  - by wobbily_col

  With normal form submission I use the pattern Post / Redirect / Get, when processing the forms. I have a database application built with Django. I want to allow the users to select a number of items from the database, then launch a computationally intensive task based on those items. I expect the task to take between 10 minutes and 2 hours to complete. Is there a standard approach to dealing with requests like this (i.e. that don't return immediately)? Ideally there would be some way to display the progress.

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