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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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  • Handling player logoff and logon in a persistent world without breaking immersion

    - by Boreal
    One problem I've never seen fixed in any persistent online game is how to handle player logon and logoff without the characters just popping in and out of the world. My first thought is to simply make a player's offline state as their character being asleep, but that doesn't make sense in the event of a disconnect and not an intentional logoff. How would you fix this, if you would even bother fixing it at all?

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  • Is there a language where collections can be used as objects without altering the behavior?

    - by Dokkat
    Is there a language where collections can be used as objects without altering the behavior? As an example, first, imagine those functions work: function capitalize(str) //suppose this *modifies* a string object capitalizing it function greet(person): print("Hello, " + person) capitalize("pedro") >> "Pedro" greet("Pedro") >> "Hello, Pedro" Now, suppose we define a standard collection with some strings: people = ["ed","steve","john"] Then, this will call toUpper() on each object on that list people.toUpper() >> ["Ed","Steve","John"] And this will call greet once for EACH people on the list, instead of sending the list as argument greet(people) >> "Hello, Ed" >> "Hello, Steve" >> "Hello, John"

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  • Designing javascript chart library

    - by coolscitist
    I started coding a chart library on top of d3js: My chart library. I read Javascript API reusability and Towards reusable charts. However, I am NOT really following the suggestions because I am not really convinced about them. This is how my library can be used to create a bubble chart: var chart = new XYBubbleChart(); chart.data = [{"xValue":200,"yValue":300},{"xValue":400,"yValue":200},{"xValue":100,"yValue":310}]; //set data chart.dataKey.x = "xValue"; chart.dataKey.y = "yValue"; chart.elementId = "#chart"; chart.createChart(); Here are my questions: It does not use chaining. Is it a big issue? Every property and function is exposed publicly. (Example: width, height are exposed in Chart.js). OOP is all about abstraction and hiding, but I don't really see the point right now. I think exposing everything gives flexibility to change property and functionality inside subclasses and objects without writing a lot of code. What could be pitfalls of such exposure? I have implemented functions like: zooming, "showing info boxes when data point is clicked" as "abilities". (example: XYZoomingAbility.js). Basically, such "abilities" accept "chart" object, play around with public variables of "chart" to add functionality. What this allows me to do is to add an ability by writing: activateZoomAbility(chartObject); My goal is to separate "visualization" from "interactivity". I want "interactivity" like: zooming to be plugged into the chart rather than built inside the chart. Like, I don't want my bubble chart to know anything about "zooming". However, I do want zoomable bubble chart. What is the best way to do this? How to test and what to test? I have written mixed tests: jasmine and actual html files so that I can test manually on browser.

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  • Callback Contract in WCF

    Callback contracts are a very powerful concept that is easily implemented in WCF. Using this, it is very easy to achieve event-like behavior between a service and client (duplex operations).

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  • Securing Back End API for Mobile Applications

    - by El Guapo
    I have an application that I am writing for both iOS and Android; this application will be served by a ReSTFUL API running on a cluster of servers on "the internets". I am curious how the rest of the world is going about securing their APIs so only specific applications running on iOS or Android can use these APIs. I could go the same route as other OAuth providers by providing a key/secret combination (2-legged OAuth), however, what do I do if I ever have to change these keys??? Do I create a new key/secret for every person that downloads the app??? The application is a social-based game that will allow the user to interact with other "participants" in the game based on location, achievements, etc. The API will provide the following functions: -Questions, Quests, etc -Profile Management -User Interaction -Possible Social Interaction Once the app gains traction I plan on opening up the API ala Facebook, Twitter, etc. Which is easy enough, I plan on implementing an OAuth Server and whatnot. However, I want to make sure, during this phase, that only people who are using the application can access and use the API.

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  • Monitoring your WCF Web Apis with AppFabric

    - by cibrax
    The other day, Ron Jacobs made public a template in the Visual Studio Gallery for enabling monitoring capabilities to any existing WCF Http service hosted in Windows AppFabric. I thought it would be a cool idea to reuse some of that for doing the same thing on the new WCF Web Http stack. Windows AppFabric provides a dashboard that you can use to dig into some metrics about the services usage, such as number of calls, errors or information about different events during a service call. Those events not only include information about the WCF pipeline, but also custom events that any developer can inject and make sense for troubleshooting issues.      This monitoring capabilities can be enabled on any specific IIS virtual directory by using the AppFabric configuration tool or adding the following configuration sections to your existing web app, <system.serviceModel> <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" /> <diagnostics etwProviderId="3e99c707-3503-4f33-a62d-2289dfa40d41"> <endToEndTracing propagateActivity="true" messageFlowTracing="true" /> </diagnostics> <behaviors> <serviceBehaviors> <behavior name=""> <etwTracking profileName="EndToEndMonitoring Tracking Profile" /> </behavior> </serviceBehaviors> </behaviors> </system.serviceModel>   <microsoft.applicationServer> <monitoring> <default enabled="true" connectionStringName="ApplicationServerMonitoringConnectionString" monitoringLevel="EndToEndMonitoring" /> </monitoring> </microsoft.applicationServer> Bad news is that none of the configuration above can be easily set on code by using the new configuration model for WCF Web stack.  A good thing is that you easily disable it in the configuration when you no longer need it, and also uses ETW, a general-purpose and high-speed tracing facility provided by the operating system (it’s part of the windows kernel). By adding that configuration section, AppFabric will start monitoring your service automatically and providing some basic event information about the service calls. You need some custom code for injecting custom events in the monitoring data. What I did here is to copy and refactor the “WCFUserEventProvider” class provided as sample in the Ron’s template to make it more TDD friendly when using IoC. I created a simple interface “ILogger” that any service (or resource) can use to inject custom events or monitoring information in the AppFabric database. public interface ILogger { bool WriteError(string name, string format, params object[] args); bool WriteWarning(string name, string format, params object[] args); bool WriteInformation(string name, string format, params object[] args); } The “WCFUserEventProvider” class implements this interface by making possible to send the events to the AppFabric monitoring database. The service or resource implementation can receive an “ILogger” as part of the constructor. [ServiceContract] [Export] public class OrderResource { IOrderRepository repository; ILogger logger;   [ImportingConstructor] public OrderResource(IOrderRepository repository, ILogger logger) { this.repository = repository; this.logger = logger; }   [WebGet(UriTemplate = "{id}")] public Order Get(string id, HttpResponseMessage response) { var order = this.repository.All.FirstOrDefault(o => o.OrderId == int.Parse(id, CultureInfo.InvariantCulture)); if (order == null) { response.StatusCode = HttpStatusCode.NotFound; response.Content = new StringContent("Order not found"); }   this.logger.WriteInformation("Order Requested", "Order Id {0}", id);   return order; } } The example above uses “MEF” as IoC for injecting a repository and the logger implementation into the service. You can also see how the logger is used to write an information event in the monitoring database. The following image illustrates how the custom event is injected and the information becomes available for any user in the dashboard. An issue that you might run into and I hope the WCF and AppFabric teams fixed soon is that any WCF service that uses friendly URLs with ASP.NET routing does not get listed as a available service in the WCF services tab in the AppFabric console. The complete example is available to download from here.

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  • Low coupling processing big quantities of data

    - by vitalik
    Usually I achieve low coupling by creating classes that exchange lists, sets, and maps between them. Now I am developing a batch application and I can't put all the data inside a data structure because there isn't enough memory. I have to read and process one chunk of data and then going to the next one. So having low coupling is much more difficult because I have to check somewhere if there is still data to read, etc. What I am using now is: Source - Process - Persist The classes that process have to ask to the Source classes if there are more rows to read. What are the best practices and or useful patterns in such situations? I hope I am explaining myself, if not tell me.

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  • Generic and type safe I/O model in any language

    - by Eduardo León
    I am looking for an I/O model, in any programming language, that is generic and type safe. By genericity, I mean there should not be separate functions for performing the same operations on different devices (read_file, read_socket, read_terminal). Instead, a single read operation works on all read-able devices, a single write operation works on all write-able devices, and so on. By type safety, I mean operations that do not make sense should not even be expressible in first place. Using the read operation on a non-read-able device ought to cause a type error at compile time, similarly for using the write operation on a non-write-able device, and so on. Is there any generic and type safe I/O model?

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  • Practical Meta Programming System (MPS)

    - by INTPnerd
    This is in regards to Meta Programming System or MPS by JetBrains. Thus far, from my efforts to learn how to use MPS, I have only learned its basic purpose and that it is very complex. Is MPS worth learning? Is there anyone who already effectively uses MPS to create their own languages and editors for those languages and uses these created editors as their primary way of programming? If so, what types of programs have they made with this? What are the advantages and disadvantages of working with MPS? What is the best way to learn MPS?

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  • Representation of data in application versus database

    - by user1815201
    I'm going to make an application that will be given data to put in a database. The data will for the most part be the same, but the way it is formatted will vary a lot (could be in anything from text files to .xls to .doc). I'm not a very experienced developer, but I can see some potential issues and I want to minimize them. First off I have decided to use the DAO pattern, so that I can easily support new file formats or file suddenly formatted in different ways. What I really wonder about though, is how I should manage the data itself within my application. I'm thinking that the database DAO should have models representing each table of the database with the same relations between them, to make the uploading process easy. But should the filesystem DAO's have to use the same models? I can imaging that when the database changes, the change will suddenly propagate throughout the entire system, all DAOs and models alike. And that is obviously a bad thing. I'm a little bit tired and out of time. Will update with what ever questions you have. Thanks!

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  • Responsive website VS mobile website

    - by Saif Bechan
    I am creating a new blog. Nowadays, especially for a blog, it's important that the websites are accessible for all devices. Now I have to make a choice on what to do. I have seen 2 options. Option 1 is to go with a normal fixed website, for example 960px wide (grid960). And for mobile users have a mobile version. This takes some more time, but then there are 2 good versions of the website. Option 2 I haven't seen a lot yet, creating a adaptive website, or also called responsive website. I am now looking into the LESS framework, where the website automatically switches to to required width. Only downside is that when the normal browser is re-sized, everything re-sizes. Another problem I found is that pinch-to-zoom on devices does not work. Now the question is, which one would you prefer for a blog. One that constantly changes layout when you move your device, or one where you have the choice to view mobile and normal. If there are any other options, please let me know.

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  • Presenting Designing an SSIS Execution Framework to Steel City SQL 18 Jan 2011!

    - by andyleonard
    I'm honored to present Designing an SSIS Execution Framework (Level 300) to Steel City SQL - the Birmingham Alabama chapter of PASS - on 18 Jan 2011! The meeting starts at 6:00 PM 18 Jan 2011 and will be held at: New Horizons Computer Learning Center 601 Beacon Pkwy. West Suite 106 Birmingham, Alabama, 35209 ( Map for directions ) Abstract In this “demo-tastic” presentation, SSIS trainer, author, and consultant Andy Leonard explains the what, why, and how of an SSIS framework that delivers metadata-driven...(read more)

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  • A talk about observer pattern

    - by Martin
    As part of a university course I'm taking, I have to hold a 10 minute talk about the observer pattern. So far these are my points: What is it? (defenition) Polling is an alternative Polling VS Observer When Observer is better When Polling is better (taken from here) A statement that Mediator pattern is worth checking out. (I won't have time to cover it in 10 minutes) I would be happy to hear about: Any suggestions to add something? Another alternative (if exists)

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  • genetic algorithm for leveling/build test

    - by Renan Malke Stigliani
    I'm starting o build a online PVP (duel like, one-to-one) game, where there is leveling, skill points, special attacks and all the common stuff. Since I never did anything like that, I'm still thinking about the maths behind the level/skill/special balances. So I thought good way of testing the best/combo builds would implement a Genetic Algorith. It'd be like that: Generate a big portion of random characters Make them fight, level them up accordingly to the victories(more XP)/losses(less XP) Mate the winners, crossing their builds, to try to make even best characters Add some more random chars, emulating new players Repeat the process for some time, or util find some chars who can beat everyone butts So I could play with the math and try to find the balance where the top x% chars would be a mix of various build types. So, is it a good idea, or there are some other easier method to do the balance? PS: I like this also, because it sounds funny

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  • Databinding to an Entity Framework in WPF

    - by King Chan
    Is it good to use databinding to Entity Framework's Entity in WPF? I created a singleton entity framework context: To have only one connection and it won't open and close all the time. So I can pass the Entity around to any class, and can modify the Entity and make changes to the database. All ViewModels getting the entity out from the same Context and databinding to the View saves me time from mapping new object, but now I imagine there is problem in not using the newest Context: A ViewModel databinding to a Entity, then someone else updated the data. The ViewModel will still display the old data, because the Context is never being dispose to refresh. I always create new Context and then dispose of it. If I want to pass the Entity around, then there will be conflicts between Context and Entity. What is the suggested way of doing this ?

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  • Procedural landscape generation but not just fractals

    - by Richard Fabian
    In large procedural landscape games, the land seems dull, but that's probably because the real world is largely dull, with only limited places where the scenery is dramatic or tactical. Looking at world generation from this point of view, a landscape generator for a game needs to not follow the rules of landscaping, but instead some rules married to the expectations of the gamer. For example, there could be a choke point / route generator that creates hills ravines, rivers and mountains between cities, rather than cities plotted on the land based on the resources or conditions generated by the mountains and rainfall patterns. Is there any existing work being done like this? Start with cities or population centres and then add in terrain afterwards?

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  • Models, controllers, and code reuse

    - by user11715
    I have a blog where users can post comments. When creating a comment, various things happen: creating the comment object, associations, persisting sending notification emails to post's author given his preferences sending notification to moderators given their preferences updating a fulltext database for search ... I could put all this in the controller, but what if I want to reuse this code ? e.g. I would like to provide an API for posting comments. I could also put this in the model, but I wonder if I won't lose flexibility by doing so. And would it be acceptable to do all of this from the model layer ? What would you do ?

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  • Multithreaded UI desktop application issues

    - by igor
    I am involved into development a rich UI project: desktop windows application. Application uses asynchronous invocations and in its turn it should be ready to process external messages (events). The problem is clear: at first time it was built as a simple prototype and it was not stress tested and all was fine. Then application was grown: the number of calls to server and number of events from server are high and performance is low. What is more users noticed that sometimes performance is extremal low. Asynchronous invocations based on thread pool (BeginInvoke, EndInvoke), external events are going from WCF service (.NET 3.5). My goal is synchronization of all tasks and putting priorities to every executions in desktop application. My question is: is there any practice how to reach my goal: patterns, task priority list, others? What should I do at first, second and next times? Thanks

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  • In retrospect, has it been a good idea to use three-valued logic for SQL NULL comparisons?

    - by Heinzi
    In SQL, NULL means "unknown value". Thus, every comparison with NULL yields NULL (unknown) rather than TRUE or FALSE. From a conceptional point of view, this three-valued logic makes sense. From a practical point of view, every learner of SQL has, one time or another, made the classic WHERE myField = NULL mistake or learned the hard way that NOT IN does not do what one would expect when NULL values are present. It is my impression (please correct me if I am wrong) that the cases where this three-valued logic helps (e.g. WHERE myField IS NOT NULL AND myField <> 2 can be shortened to WHERE myField <> 2) are rare and, in those cases, people tend to use the longer version anyway for clarity, just like you would add a comment when using a clever, non-obvious hack. Is there some obvious advantage that I am missing? Or is there a general consensus among the development community that this has been a mistake?

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  • Cluster Nodes as RAID Drives

    - by BuckWoody
    I'm unable to sleep tonight so I thought I would push this post out VERY early. When you don't sleep your mind takes interesting turns, which can be a good thing. I was watching a briefing today by a couple of friends as they were talking about various ways to arrange a Windows Server Cluster for SQL Server. I often see an "active" node of a cluster with a "passive" node backing it up. That means one node is working and accepting transactions, and the other is not doing any work but simply "standing by" waiting for the first to fail over. The configuration in the demonstration I saw was a bit different. In this example, there were three nodes that were actively working, and a fourth standing by for all three. I've put configurations like this one into place before, but as I was looking at their architecture diagram, it looked familar - it looked like a RAID drive setup! And that's not a bad way to think about your cluster arrangements. The same concerns you might think about for a particular RAID configuration provides a good way to think about protecting your systems in general. So even if you're not staying awake all night thinking about SQL Server clusters, take this post as an opportunity for "lateral thinking" - a way of combining in your mind the concepts from one piece of knowledge to another. You might find a new way of making your technical environment a little better. Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • Is it a "pattern smell" to put getters like "FullName" or "FormattedPhoneNumber" in your model?

    - by DanM
    I'm working on an ASP.NET MVC app, and I've been getting into the habit of putting what seem like helpful and convenient getters into my model/entity classes. For example: public class Member { public int Id { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public string PhoneNumber { get; set; } public string FullName { get { return FirstName + " " + LastName; } } public string FormattedPhoneNumber { get { return "(" + PhoneNumber.Substring(0, 3) + ") " + PhoneNumber.Substring(3, 3) + "-" + PhoneNumber.Substring(6); } } } I'm wondering people think about the FullName and FormattedPhoneNumber getters. They make it very easy to create standardized data formats throughout the app, and they seem to save a lot of repeated code, but it could definitely be argued that data format is something that should be handled in mapping from model to view-model. In fact, I was originally applying these data formats in my service layer where I do my mapping, but it was becoming a burden to constantly have to write formatters then apply them in many different places. E.g., I use "Full Name" in most views, and having to type something like model.FullName = MappingUtilities.GetFullName(entity.FirstName, entity.LastName); all over the place seemed a lot less elegant than just typing model.FullName = entity.FullName (or, if you use something like AutoMapper, potentially not typing anything at all). So, where do you draw the line when it comes to data formatting. Is it "okay" to do data formatting in your model or is that a "pattern smell"? Note: I definitely do not have any html in my model. I use html helpers for that. I'm strictly talking about formatting or combining data (and especially data that is frequently used).

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  • Adventures in the Land of CloudDB/NoSQL/NoAcid

    - by KKline
    Cloud, Bunny, or CloudBunny? Last year, some of my friends from Quest Software attended Hadoop World in New York. In 2009, I never would've guessed that Quest would be there with products, community initiatives, as a major sponsor and with presenters? There were just under 1,000 attendees who weren’t the typical devheads and geekasaurs you'd normally see at very techie events like Code Camps, SQL Saturdays, Cloud Camps and or even other NoSQL events such as the Cassandra Summit. We're talkin' enterprise...(read more)

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  • Configuration data: single-row table vs. name-value-pair table

    - by Heinzi
    Let's say you write an application that can be configured by the user. For storing this "configuration data" into a database, two patterns are commonly used. The single-row table CompanyName | StartFullScreen | RefreshSeconds | ... ---------------+-------------------+------------------+-------- ACME Inc. | true | 20 | ... The name-value-pair table ConfigOption | Value -----------------+------------- CompanyName | ACME Inc. StartFullScreen | true (or 1, or Y, ...) RefreshSeconds | 20 ... | ... I've seen both options in the wild, and both have obvious advantages and disadvantages, for example: The single-row tables limits the number of configuration options you can have (since the number of columns in a row is usually limited). Every additional configuration option requires a DB schema change. In a name-value-pair table everything is "stringly typed" (you have to encode/decode your Boolean/Date/etc. parameters). (many more) Is there some consensus within the development community about which option is preferable?

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  • How to ...set up new Java environment - largely interfaces...

    - by Chris Kimpton
    Hi, Looks like I need to setup a new Java environment for some interfaces we need to build. Say our system is X and we need to interfaces to systems A, B and C. Then we will be writing interfaces X-A, X-B, X-C. Our system has a bus within it, so the publishing on our side will be to the bus and the interface processes will be taking from the bus and mapping to the destination system. Its for a vendor based system - so most of the core code we can't touch. Currently thinking we will have several processes, one per interface we need to do. The question is how to structure things. Several of the APIs we need to work with are Java based. We could go EJB, but prefer to keep it simple, one process per interface, so that we can restart them individually. Similarly SOA seems overkill, although I am probably mixing my thoughts about implementations of it compared to the concepts behind it... Currently thinking that something Spring based is the way to go. In true, "leverage a new tech if possible"-style, I am thinking maybe we can shoe horn some jruby into this, perhaps to make the APIs more readable, perhaps event-machine-like and to make the interface code more business-friendly, perhaps even storing the mapping code in the DB, as ruby snippets that get mixed in... but thats an aside... So, any comments/thoughts on the Spring approach - anything more up-to-date/relevant these days. EDIT: Looking a JRuby further, I am tempted to write it fully in JRuby... in which case do we need any frameworks at all, perhaps some gems to make things clearer... Thanks in advance, Chris

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