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• How can I find the shortest path between two subgraphs of a larger graph?

  - by Pops

  I'm working with a weighted, undirected multigraph (loops not permitted; most node connections have multiplicity 1; a few node connections have multiplicity 2). I need to find the shortest path between two subgraphs of this graph that do not overlap with each other. There are no other restrictions on which nodes should be used as start/end points. Edges can be selectively removed from the graph at certain times (as explained in my previous question) so it's possible that for two given subgraphs, there might not be any way to connect them. I'm pretty sure I've heard of an algorithm for this before, but I can't remember what it's called, and my Google searches for strings like "shortest path between subgraphs" haven't helped. Can someone suggest a more efficient way to do this than comparing shortest paths between all nodes in one subgraph with all nodes in the other subgraph? Or at least tell me the name of the algorithm so I can look it up myself? For example, if I have the graph below, the nodes circled in red might be one subgraph and the nodes circled in blue might be another. The edges would all have positive integer weights, although they're not shown in the image. I'd want to find whatever path has the shortest total cost as long as it starts at a red node and ends at a blue node. I believe this means the specific node positions and edge weights cannot be ignored. (This is just an example graph I grabbed off Wikimedia and drew on, not my actual problem.)

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• Spring MVC vs raw servlets and template engine?

  - by Gigatron

  I've read numerous articles about the Spring MVC framework, and I still can't see the benefits of using it. It looks like writing even a simple application with it requires creating a big hodgepodge of XML files and annotations and other reams of code to conform to what the framework wants, a whole bunch of moving parts to accomplish a simple single task. Any time I look at a Spring example, I can see how I can write something with the same functionality using a simple servlet and template engine (e.g. FreeMarker, StringTemplate), in half the lines of code and little or no XML files and other artifacts. Just grab the data from the session and request, call the application domain objects if necessary, pass the results to the template engine to generate the resulting web page, done. What am I missing? Can you describe even one example of something that is actually made simpler with Spring than using a combination of raw servlets with a template engine? Or is Spring MVC just one of those overly complicated things that people use only because their boss tells them to use it?

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• How to TDD test that objects are being added to a collection if the collection is private?

  - by Joshua Harris

  Assume that I planned to write a class that worked something like this: public class GameCharacter { private Collection<CharacterEffect> _collection; public void Add(CharacterEffect e) { ... } public void Remove(CharacterEffect e) { ... } public void Contains(CharacterEffect e) { ... } } When added an effect does something to the character and is then added to the _collection. When it is removed the effect reverts the change to the character and is removed from the _collection. It's easy to test if the effect was applied to the character, but how do I test that the effect was added to _collection? What test could I write to start constructing this class. I could write a test where Contains would return true for a certain effect being in _collection, but I can't arrange a case where that function would return true because I haven't implemented the Add method that is needed to place things in _collection. Ok, so since Contains is dependent on having Add working, then why don't I try to create Add first. Well for my first test I need to try and figure out if the effect was added to the _collection. How would I do that? The only way to see if an effect is in _collection is with the Contains function. The only way that I could think to test this would be to use a FakeCollection that Mocks the Add, Remove, and Contains of a real collection, but I don't want _collection being affected by outside sources. I don't want to add a setEffects(Collection effects) function, because I do not want the class to have that functionality. The one thing that I am thinking could work is this: public class GameCharacter<C extends Collection> { private Collection<CharacterEffect> _collection; public GameCharacter() { _collection = new C<CharacterEffect>(); } } But, that is just silly making me declare what some private data structures type is on every declaration of the character. Is there a way for me to test this without breaking TDD principles while still allowing me to keep my collection private?

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• Is ASP.NET MVC too much overhead for smaller projects?

  - by Alexander Ryan Baggett

  I will be honest I don't really know much about MVC other than the stuff you can read online in 5 minutes. Unfortunately this doesn't really tell me whether its suited to smaller projects or not. I also read this related question and its chosen answer, but the business perspective is not a concern in this case for me as I am the only one making it. The next answer proceeds to say why it is more flexible. Sure, that's great. But my question is again, if its an ideal choice for a small project. For example I would rather use winforms to make a simple mockup of a small desktop program than do it on WPF because of the overhead of custom styling. So I have a project that will essentially have about 6-8 pages that read excel files and user input use that to pull a bit of data from databases and output resulting excel files. I will be the only one working on this project. If I used webforms I would expect it to take no more than 2-3 weeks. Now I am 100% comfortable with webforms. And I know its easy to do a small project in webforms. But I have only heard good things about MVC so I am seriously considering it.

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• Environment naming standards in software development?

  - by Marcus_33

  My project is currently suffering from environment naming issues. Different people have different assumptions as to what environments should be named or what the names designate, and it's causing confusion when discussing them. I've done a bit of research and I haven't found any standards out there. The terms include "Local", "Sand", "Dev", "Test", "User", "QA", "Staging" and "Prod" (plus a few more that different people have asked about) I'm not looking for just opinions, though if there's one out there that "everyone" has I'll take it - I'm trying to find definitions advanced by some sort of authority, even if it's unofficial. Here's the environments we currently use: Environment on the developer's PC Shared Environment where developers directly upload code to self-test Shared Environment where standards and functionality are tested by QA people Shared Environment where completed and QA-checked code is approved by project requesters Environment that mirrors the final environment as a final check and to prepare for deployment Final Environment where code is in use I know what I'd call them, but is there some sort of standard on this? Thanks in advance.

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• Does it ever make sense to license source code as a learning resource under GPL?

  - by Earlz

  I recently came across a series of articles walking through how to make a scheme interpreter. I was browsing through the code when I realized that it was AGPL. For the most part, the code itself is the teaching tool. Basically, the code as-is is what I need, however, I did want to understand how it all fits together as well. I realized though that if I copy and paste a single line of code, my project would become AGPL. Possibly by even more trivial actions? Anyway, is this a standard practice at all? Am I just being over-paranoid? Also, what benefits are there to this licensing scheme?

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• Get entities ids from two similar collections using one method

  - by Patryk Roszczyniala

  I've got two lists: List<Integer, ZooEntity> zoos; List<Integer, List<ZooEntity>> groupOfZoos; These operations will return collections of values: Collection<ZooEntity> cz = zoos.values(); Collection<List<ZooEntity>> czList = groupOfZoos.values(); What I want to achieve is to get list of all zoo ids. List<Integer> zooIds = cz ids + czList ids; Of course I can create two methods to do what I want: public List<Integer> getIdsFromFlatList(Collection<ZooEntity> list) { List<Integer> ids = new ArrayList<Integer>(); for (ZooEntity z : list) { ids.add(z.getId()); } return ids; } public List<Integer> getIdsFromNestedList(Collection<List<ZooEntity>> list) { List<Integer> ids = new ArrayList<Integer>(); for (List<ZooEntity> zList : list) { for (ZooEntity z : zList) { ids.add(z.getId()); } } return ids; } As you can see those two methods are very similar and here is my question: Is it good to create one method (for example using generics) which will get ids from those two lists (zoos and groupOfZoos). If yes how it should look like? If no what is the best solution? BTW. This is only the example. I've got very similar problem at job and I want to do it in preety way (I can't change enities, I can change only getIds...() methods).

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• What to choose API based server or Socket based server for data driven application

  - by Imdad

  I am working on a project which has a Desktop Application for MAC/COCOA, a native application for iPhone another native application in iPad. All the application do almost same thing. The applications are data driven applications. Every communication to server is made via a restful API developed in PHP. When a user logs in a lot of data is fetched from server. And to remain in sync with server pooling is done. As there are lot of data to pool it makes application slower and un-reliable. A possible solution that comes into my mind is to use Socket based server. My question is that will it reasonably improve the performance? And which technology (of sockets) will be good as a server side solution for data driven application? I have heard a lot about Node.js. Please give your suggestions.

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• Design pattern for an ASP.NET project using Entity Framework

  - by MPelletier

  I'm building a website in ASP.NET (Web Forms) on top of an engine with business rules (which basically resides in a separate DLL), connected to a database mapped with Entity Framework (in a 3rd, separate project). I designed the Engine first, which has an Entity Framework context, and then went on to work on the website, which presents various reports. I believe I made a terrible design mistake in that the website has its own context (which sounded normal at first). I present this mockup of the engine and a report page's code behind: Engine (in separate DLL): public Engine { DatabaseEntities _engineContext; public Engine() { // Connection string and procedure managed in DB layer _engineContext = DatabaseEntities.Connect(); } public ChangeSomeEntity(SomeEntity someEntity, int newValue) { //Suppose there's some validation too, non trivial stuff SomeEntity.Value = newValue; _engineContext.SaveChanges(); } } And report: public partial class MyReport : Page { Engine _engine; DatabaseEntities _webpageContext; public MyReport() { _engine = new Engine(); _databaseContext = DatabaseEntities.Connect(); } public void ChangeSomeEntityButton_Clicked(object sender, EventArgs e) { SomeEntity someEntity; //Wrong way: //Get the entity from the webpage context someEntity = _webpageContext.SomeEntities.Single(s => s.Id == SomeEntityId); //Send the entity from _webpageContext to the engine _engine.ChangeSomeEntity(someEntity, SomeEntityNewValue); // <- oops, conflict of context //Right(?) way: //Get the entity from the engine context someEntity = _engine.GetSomeEntity(SomeEntityId); //undefined above //Send the entity from the engine's context to the engine _engine.ChangeSomeEntity(someEntity, SomeEntityNewValue); // <- oops, conflict of context } } Because the webpage has its own context, giving the Engine an entity from a different context will cause an error. I happen to know not to do that, to only give the Engine entities from its own context. But this is a very error-prone design. I see the error of my ways now. I just don't know the right path. I'm considering: Creating the connection in the Engine and passing it off to the webpage. Always instantiate an Engine, make its context accessible from a property, sharing it. Possible problems: other conflicts? Slow? Concurrency issues if I want to expand to AJAX? Creating the connection from the webpage and passing it off to the Engine (I believe that's dependency injection?) Only talking through ID's. Creates redundancy, not always practical, sounds archaic. But at the same time, I already recuperate stuff from the page as ID's that I need to fetch anyways. What would be best compromise here for safety, ease-of-use and understanding, stability, and speed?

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• Should companies require developers to credit code they didn't write?

  - by sunpech

  In academia, it's considered cheating if a student copies code/work from someone/somewhere else without giving credit, and tries to pass it off as his/her own. Should companies make it a requirement for developers to properly credit all non-trivial code and work that they did not produce themselves? Is it useful to do so, or is it simply overkill? I understand there are various free licenses out there, but if I find stuff I like and actually use, I really feel compelled to give credit via comment in code even if it's not required by the license (or lack thereof one).

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• save data in the database to xml in c [closed]

  - by Jayanth N

  I have some data in the database. I want those data in database to be stored as an xml file. I'm using postgresql 9.1 for database, for xml processing I'm using libxml (http://xmlsoft.org/). I'm writing the code in C language. Please help me. Detailed explanation: I have a client, which sends me a xml file. Server receives the xml file, parses the xml file and stores it in the db. From db i want to send the details in the form of an xml to the client. client: <employee> <name>glen</name> <telephone>123456789</telephone> </employee> <employee> <name>gwen</name> <telephone>123456789</telephone> </employee> server parses this xml file as displayed below: name : glen telephone:123456789 name : gwen telephone: 123456789 and saves it in a database(postgresql9.1) if the client requests for details of the employees, i've to send it in xml form from database.I don't know how to do it can u help me out.

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• how do you read from system.out in Java [closed]

  - by Dan

  I'm trying to create a word scramble game and so far I have taken a vector of randomly assorted strings that contains both words and hints and split them into two vectors. I have randomly scrambled the word and set this all up in text boxes. Right now I'm stuck because I have a text box that takes input but I'm not sure how to read that in? I want the user to type the unscrambled word into the text box and have it calculate as correct and move on to the next word immediately. I also don't know how to get the keys working. I want the "?" character to be the hint button that shows the hint. At the moment the hint box works if I type the question mark in using the System.in but it doesn't work if I type it directly in to the text box. The characters are showing up in the text box but nothing is working after that.

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• What are the most important concepts to understand for "fluency in developer English"?

  - by Edward Tanguay

  In April, I'm going to be giving a talk called **English 2.0 - Understanding the Language of Developers" to a group of English teachers. The purpose is in two hours to give them a quick background in key concepts so that they can better understand developer blogs and podcasts and are able to ask better questions when talking to developers. What do you think are the most important concepts to understand, concepts that developers take for granted but the general public is not familiar with? Here are a few ideas: version control abstractions pub/sub push vs. pull debugging modularity three-tier architecture class/object "spaghetti code" vs. OOP exception throwing crowd sourcing refactoring the cloud DRY - don't repeat yourself client/server unit testing designer/developer

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• Finding an A* heuristic for a directed graph

  - by Janis Peisenieks

  In a previous question, I asked about finding a route (or path if you will) in a city. That is all dandy. The solution I chose was with the A* algorithm, which really seems to suit my needs. What I find puzzling is heuristic. How do I find one in an environment without constant distance between 2 nodes? Meaning, not every 2 nodes have the same distance between them. What I have is nodes (junctures), streets with weight (which may also be one-way), a start/finish node (since the start and end is always in the same place) and a goal node. In an ordinary case, I would just use the same way I got to goal to go back, but since one of the streets could have been a one-way, that may not be possible. The main question How do I find a heuristic in a directed graph?

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• What are unique aspects of a software Lifecycle of an attack/tool on a software vulnerability?

  - by David Kaczynski

  At my local university, there is a small student computing club of about 20 students. The club has several small teams with specific areas of focus, such as mobile development, robotics, game development, and hacking / security. I am introducing some basic agile development concepts to a couple of the teams, such as user stories, estimating complexity of tasks, and continuous integration for version control and automated builds/testing. I am familiar with some basic development life-cycles, such as waterfall, spiral, RUP, agile, etc., but I am wondering if there is such a thing as a software development life-cycle for hacking / breaching security. Surely, hackers are writing computer code, but what is the life-cycle of that code? I don't think that they would be too concerned with maintenance, as once the breach has been found and patched, the code that exploited that breach is useless. I imagine the life-cycle would be something like: Find gap in security Exploit gap in security Procure payload Utilize payload What kind of differences (if any) are there for the development life-cycle of software when the purpose of the product is to breach security?

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• How much is modern programming still tied to underyling digital logic?

  - by New Talk

  First of all: I've got no academic background. I'm working primarily with Java and Spring and I'm also fond of web programming and relational databases. I hope I'm using the right terms and I hope that this vague question makes some sense. Today the following question came to my mind: How much is modern programming still tied to the underlying digital logic? With modern programming I mean concepts like OOP, AOP, Java 7, AJAX, … I hope you get the idea. Do they no longer need the digital logic with which computers are working internally? Or is binary logic still ubiquitous when programming this way? If I'd change the inner workings of a computer overnight, would it matter, because my programming techniques are already that abstract? P. S.: With digital logic I mean the physical representation of everything "inside" the computer as zeroes and ones. Changed "binary" to "digital".

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• Are there good resources for leading documentation for an existing software product having none?

  - by Ben Rose

  Hello. I'm a software developer at a technology company. I have been tasked with leading the documentation effort for the product I work on, both internal to developers as well as spilling over into facilitating the business side of requirements documentation. This internal product has been around for at least 6 years. One challenge is that this software application has no form of documentation other than some small, outdated pieces here and there. There are comments in the code, but they are technical and do not convey any over-arching behavior (even on technical side). As a consequence of having little to no documentation, this product is often unnecessarily complex under the covers adding to the challenge. We are very limited on time that will be given to us to work on documentation. Another thing about me is that I've displayed some ability in writing/communication around the office, but I'm not coming from any sort of documentation or formal writing background (beyond my academic career). Please share your advise or recommend resources, book/website/forum/whatever, for helping me come up with a plan with milestones, best practices, task delegation, templates, buy-in, etc. I'm hoping for a resource targeting or giving special mention of introducing good documentation on existing projects where there previously was none. I would be very grateful for your responses. Ben

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• storing data for maps database

  - by Timigen

  I am working on an application that displays choropleth maps. These maps are of all different types, some display state by county, country by state/province, or world by country. How should I handle storing the map information in the database? My Thoughts: I won't need to do queries to find POI inside a region, so I don't think there is a need to use spatial datatypes. I am considering storing a map as a geoJSON object (I am using JS mapping library that accepts geoJSON). The only issue is what if I want a map of the US northeast. Then I would have geoJSON for the US and a separate one for the US northeast, which would be redundant. Would it make sense to have a shape database where I had each state then when I needed a map of the US I could query for each state, and when I needed a map of the US Northeast I could again query for what I need? Note: I am not concerned with storing the data for each region, just the region itself. I will query for the data on the fly for the specific region.

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• ASP.NET MVC WebService - Security for Industrial Android Clients

  - by Chris Nevill

  I'm trying to design a system that will allow a bunch of Android devices to securely log into an ASP.NET MVC REST Web service. At present neither side are implemented. However there is an ASP.NET MVC website which the web service will site along side. This is currently using forms authentication. The idea will be that the Android devices will download data from the web service and then be able to work offline storing data in their own local databases, where users will be able to make updates to that data, and then syncing updates back to the main server where possible. The web service will be using HTTPS to prevent calls being intercepted and reduce the risk of calls being intercepted. The system is an industrial system and will not be in used by the general Android population. Instead only authorized Android devices will be authorized by the Web Service to make calls. As such I was thinking of using the Android devices serial number as a username and then a generated long password which the device will be able to pick up - once the device has been authorized server side. The device will also have user logins - but these will not be to log into the web service - just the device itself - since the device and user must be able to work offline. So usernames and passwords will be downloaded and stored on the devices themselves. My question is... what form of security is best setup on the web service? Should it use forms Authentication? Should the username and password just be passed in with each GET/POST call or should it start a session as I have with the website? The Android side causes more confusion. There seems to be a number of options here Spring-Android, Volley, Retrofit, LoopJ, Robo Spice which seems to use the aforementioned Spring, Retrofit or Google HttpClient. I'm struggling to find a simple example which authenticates with a forms based authentication system. Is this because I'm going about this wrong? Is there another option that would better suite this?

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• Why don't xUnit frameworks allow tests to run in parallel?

  - by Xavier Nodet

  Do you know of any xUnit framework that allows to run tests in parallel, to make use of multiple cores in today's machine? I don't... If none (or so few) of them does it, maybe there is a reason... Is it that tests are usually so quick that people simply don't feel the need to paralellize them? Is there something deeper that precludes distributing (at least some of) the tests over multiple threads? Thanks!

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• A new CAPTCHA using sentences?

  - by Xeoncross

  I was just thinking about how recaptcha is getting harder when I thought about another posible solution. Images won't last forever so we will need something else some day - like human logic or emotion. Google and others are trying grouping images by category (find the image that doesn't belong) but that requires a large amount of images and doesn't work for the blind. Anyway, what if a massive collection of text was gathered (public-domain books from each language) and a sentence was shown to the user with 1 (or 2) words that were a select box of choices? Only computers that knew correct English/Spanish/German grammar would be able to tell which of the words belonged in the sentence. Would there be any problems with this approach? I would assume that it would be easy enough for anyone that knew the language that the sentense was displayed in to figure out the answer easier than trying to read the reCAPTCHA text. Plus, storing an insane number of sentences would only take a couple gigabytes of space and wouldn't take anywhere near the CPU time creating images/audio takes. In other words, anyone could host their own captcha system with minimal impact on system performance. Is there a problem with this approach? More specifically I'm looking for the main problem with this approach. migrated from stackoverflow

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• How to find Sub-trees in non-binary tree

  - by kenny

  I have a non-binary tree. I want to find all "sub-trees" that are connected to root. Sub-tree is a a link group of tree nodes. every group is colored in it's own color. What would be be the best approach? Run recursion down and up for every node? The data structure of every treenode is a list of children, list of parents. (the type of children and parents are treenodes) Clarification: Group defined if there is a kind of "closure" between nodes where root itself is not part of the closure. As you can see from the graph you can't travel from pink to other nodes (you CAN NOT use root). From brown node you can travel to it's child so this form another group. Finally you can travel from any cyan node to other cyan nodes so the form another group

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• Is it just me or is this a baffling tech interview question

  - by Matthew Patrick Cashatt

  Background I was just asked in a tech interview to write an algorithm to traverse an "object" (notice the quotes) where A is equal to B and B is equal to C and A is equal to C. That's it. That is all the information I was given. I asked the interviewer what the goal was but apparently there wasn't one, just "traverse" the "object". I don't know about anyone else, but this seems like a silly question to me. I asked again, "am I searching for a value?". Nope. Just "traverse" it. Why would I ever want to endlessly loop through this "object"?? To melt my processor maybe?? The answer according to the interviewer was that I should have written a recursive function. OK, so why not simply ask me to write a recursive function? And who would write a recursive function that never ends? My question: Is this a valid question to the rest of you and, if so, can you provide a hint as to what I might be missing? Perhaps I am thinking too hard about solving real world problems. I have been successfully coding for a long time but this tech interview process makes me feel like I don't know anything. Final Answer: CLOWN TRAVERSAL!!! (See @Matt's answer below) Thanks! Matt

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• Is LINQ to objects a collection of combinators?

  - by Jimmy Hoffa

  I was just trying to explain the usefulness of combinators to a colleague and I told him LINQ to objects are like combinators as they exhibit the same value, the ability to combine small pieces to create a single large piece. Though I don't know that I can call LINQ to objects combinators. I've seen 2 levels of definition for combinator that I generalize as such: A combinator is a function which only uses things passed to it A combinator is a function which only uses things passed to it and other standard atomic functions but not state The first is very rigid and can be seen in the combinatory calculus systems and in haskell things like $ and . and various similar functions meet this rule. The second is less rigid and would allow something like sum as it uses the + function which was not passed in but is standard and not stateful. Though the LINQ extensions in C# use state in their iteration models, so I feel I can't say they're combinators. Can someone who understands the definition of a combinator more thoroughly and with more experience in these realms give a distinct ruling on this? Are my definitions of 'combinator' wrong to begin with?

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• Inheritance, commands and event sourcing

  - by Arthis

  In order not to redo things several times I wanted to factorize common stuff. For Instance, let's say we have a cow and a horse. The cow produces milk, the horse runs fast, but both eat grass. public class Herbivorous { public void EatGrass(int quantity) { var evt= Build.GrassEaten .WithQuantity(quantity); RaiseEvent(evt); } } public class Horse : Herbivorous { public void RunFast() { var evt= Build.FastRun; RaiseEvent(evt); } } public class Cow: Herbivorous { public void ProduceMilk() { var evt= Build.MilkProduced; RaiseEvent(evt); } } To eat Grass, the command handler should be : public class EatGrassHandler : CommandHandler<EatGrass> { public override CommandValidation Execute(EatGrass cmd) { Contract.Requires<ArgumentNullException>(cmd != null); var herbivorous= EventRepository.GetById<Herbivorous>(cmd.Id); if (herbivorous.IsNull()) throw new AggregateRootInstanceNotFoundException(); herbivorous.EatGrass(cmd.Quantity); EventRepository.Save(herbivorous, cmd.CommitId); } } so far so good. I get a Herbivorous object , I have access to its EatGrass function, whether it is a horse or a cow doesn't matter really. The only problem is here : EventRepository.GetById<Herbivorous>(cmd.Id) Indeed, let's imagine we have a cow that has produced milk during the morning and now wants to eat grass. The EventRepository contains an event MilkProduced, and then come the command EatGrass. With the CommandHandler, we are no longer in the presence of a cow and the herbivorious doesn't know anything about producing milk . what should it do? Ignore the event and continue , thus allowing the inheritance and "general" commands? or throw an exception to forbid execution, it would mean only CowEatGrass, and HorseEatGrass might exists as commands ? Thanks for your help, I am just beginning with these kinds of problem, and I would be glad to have some news from someone more experienced.

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