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• Do you think Scala will be the dominant JVM langauge, ie be the next Java? [on hold]

  - by user1037729

  From what I've read about Scala do far I think it has some nice features but I do not think it should be "the next Java". It might however end up being the next Java (due to fashion rather than fact) but lets not hope it does not... To me adds a lot of complexity over Java which is a simple and scalable language. Scala Pattern matching allows you to perform some type/value checking in a more concise way, this is possible in Java, Scala's pattern matching has a limit to it, you cannot continuously match deeper and deeper down the object graph, so why not just stick to Java and use decent invariants? Scala provides tuples, easy enough to make in Java, create a static factory method and it all reads nicely too. Scala provides mixins, why not just use composition? I believe Scala implicit's are bad, they can lead to code becoming complex and hard to maintain, explicitness is good. Scala provides closures, well they will be in Java 8 too. Scala has lazy keyword for lazy instantiation, this is easy enough to do in Java by calling a getter which creates the instance when needed, no hidden magic here. Scala can be used with AKKA, well so can Java, there is an Java AKKA implementation. Scala offers addition functional features but these can all be created in Java, there are many frameworks with have implemented functional features in Java. All in all Scala seems to offer is addition complexity and thats it...

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• Is creating a separate pool for each individual png image in the same class appropriate?

  - by Panzercrisis

  I'm still possibly a little green about object-pooling, and I want to make sure something like this is a sound design pattern before really embarking upon it. Take the following code (which uses the Starling framework in ActionScript 3): [Embed(source = "/../assets/images/game/misc/red_door.png")] private const RED_DOOR:Class; private const RED_DOOR_TEXTURE:Texture = Texture.fromBitmap(new RED_DOOR()); private const m_vRedDoorPool:Vector.<Image> = new Vector.<Image>(50, true); . . . public function produceRedDoor():Image { // get a Red Door image } public function retireRedDoor(pImage:Image):void { // retire a Red Door Image } Except that there are four colors: red, green, blue, and yellow. So now we have a separate pool for each color, a separate produce function for each color, and a separate retire function for each color. Additionally there are several items in the game that follow this 4-color pattern, so for each of them, we have four pools, four produce functions, and four retire functions. There are more colors involved in the images themselves than just their predominant one, so trying to throw all the doors, for instance, in a single pool, and then changing their color properties around isn't going to work. Also the nonexistence of the static keyword is due to its slowness in AS3. Is this the right way to do things?

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• How to prevent duplicate data access methods that retrieve similar data?

  - by Ronald Wildenberg

  In almost every project I work on with a team, the same problem seems to creep in. Someone writes UI code that needs data and writes a data access method: AssetDto GetAssetById(int assetId) A week later someone else is working on another part of the application and also needs an AssetDto but now including 'approvers' and writes the following: AssetDto GetAssetWithApproversById(int assetId) A month later someone needs an asset but now including the 'questions' (or the 'owners' or the 'running requests', etc): AssetDto GetAssetWithQuestionsById(int assetId) AssetDto GetAssetWithOwnersById(int assetId) AssetDto GetAssetWithRunningRequestsById(int assetId) And it gets even worse when methods like GetAssetWithOwnerAndQuestionsById start to appear. You see the pattern that emerges: an object is attached to a large object graph and you need different parts of this graph in different locations. Of course, I'd like to prevent having a large number of methods that do almost the same. Is it simply a matter of team discipline or is there some pattern I can use to prevent this? In some cases it might make sense to have separate methods, i.e. getting an asset with running requests may be expensive so I do not want to include these all the time. How to handle such cases?

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• Clean MVC design when there is viewer latency

  - by Tony Suffolk 66

  It isn't clear if this question has already been answered, so apologies in advance if this is a duplicate : I am implementing a game and trying to design around a clean MVC pattern - so my Control plane will implement the rules of the game (but not how the game is displayed), and the View plane implements how the game is displayed, and user iteraction - i.e. what game items or controls the user has activated. The challenge that I have is this : In my game the Control Plane can move game items more or less instaneously (The decision about what item to place where - and some of the initial consequences of that placement are reasonably trivial to calculate), but I want to design the Control Plane so that the View plane can display these movements either instaneously or using movement animations. The other complication is that player interaction must be locked out while those game items are moving (similar to chess - you can't attack an opposing piece as it moves past one of your pieces) So do I : Implement all the logic in the Control Plane asynchronously - and separate the descision making from the actions - so the Control plane decides piece 'A' needs to move to a given place - tells the view plane, and but does not implement the move in data until the view plane informs the control plane that the move/animation is complete. A lot of interlock points between the two layers. Implement all the control plane logic in one place - decisions and movement (keeping track of what moved where), and pass all the movements in one go to the View plane to do with what it will. Control Plane is almost fire and forget here. A hybrid of 1 & 2 - The control plane implements all the moves in a temporary data store - but maintains a second store which reflects what is actually visible to the viewer, based on calls and feedback from the View plane. All 3 are relatively easy to implement (target language is python), but having never done a clean MVC pattern with view latency before - I am not sure which design is best

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• DDDNorth2 Bradford, 13th October 2012 - Async Patterns presentation and source code

  - by Liam Westley

  Many thanks to Andy Westgarth and his team for organising a fantastic conference at the rather elegant Bradford University School of Management. Also, a big congratulations to all the delegates who gave up there free time to come and hear us speak and who were, in general, enthusiastic and asked some cracking questions to keep us speakers on our toes. For those who attended my Async my source code and presentation are now available on GitHub, https://github.com/westleyl/DDDNorth2-AsyncPatterns If you are new to Git then the easiest client to install is GitHub for Windows, a graphical UI for accessing GitHub. Personally, I also have TortoiseGit installed – the file explorer add-in that works in a familiar manner to TortoiseSVN. As I mentioned during the presentation I have not included the sample data, the music files, in the source code placed on GitHub but I have included instructions on how to download them from http://silents.bandcamp.com and place them in the correct folders. What I forgot to mention is that Windows Media Player by default does not play Ogg Vorbis and Flac music files, however you can download the codec installer for these, for free, from http://xiph.org/dshow. I am planning to break down this little project into a series of blog posts, with each pattern being a single blog post over several weeks. In these I will flesh out the background behind the pattern, the basic goal being achieved and how to monitor the progress of the sample data being processed. Basically, what I said during the presentation and is missing from the slides.

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• Unnamed Refactoring

  - by Liam McLennan

  This post is a message in a bottle. It cast it into the sea in the hope that it will one day return to me, stuffed to the cork with enlightenment. Yesterday I  tweeted, what is the name of the pattern where you replace a multi-way conditional with an associative array? I said ‘pattern’ but I meant ‘refactoring’. Anyway, no one replied so I will describe the refactoring here. Programmers tend to think imperatively, which leads to code such as: public int GetPopulation(string country) { if (country == "Australia") { return 22360793; } else if (country == "China") { return 1324655000; } else if (country == "Switzerland") { return 7782900; } else { throw new Exception("What ain't no country I ever heard of. They speak English in what?"); } } which is horrid. We can write a cleaner version, replacing the multi-way conditional with an associative array, treating the conditional as data: public int GetPopulation(string country) { if (!Populations.ContainsKey(country)) throw new Exception("The population of " + country + " could not be found."); return Populations[country]; } private Dictionary<string, int> Populations { get { return new Dictionary<string, int> { {"Australia", 22360793}, {"China", 1324655000}, {"Switzerland", 7782900} }; } } Does this refactoring already have a name? Otherwise, I propose Replace multi-way conditional with associative array

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• Creating an update method in a different class

  - by Sweta Dwivedi

  I have created a class called 3D model which will animate my 3D model by changing the model position according to the values based in a .txt file through a list... Since i'm using a foreach loop to read the point values when it reaches the end of the file.. XNA throws an out of bounds exception .. (which is obvious) but if i add the same code in my Game.cs update(gameTime) method.. then i dont have this problem..Any idea how to make my 3D model update work same as the update in game.cs .. Here is the code for some idea: public void patterns(GameTime gameTime) { motion_z = new List<Point3D>(); if (pattern == 1) { f = "E:/Motion_Track-output/Output1.txt"; } if (pattern == 2) { f = "E:/Motion_Track-output/cruse.txt"; } // TODO: Add your update logic here using (StreamReader r = new StreamReader(f)) { string line; //Viewport view = graphics.GraphicsDevice.Viewport; int maxWidth = view.Width; int maxHeight = view.Height; while ((line = r.ReadLine()) != null) { string[] temp = line.Split(','); int x = (int)Math.Floor(((float.Parse(temp[0]) * 0.5f) + 0.5f) * maxWidth); int y = (int)Math.Floor(((float.Parse(temp[1]) * -0.5f) + 0.5f) * maxHeight); int z = (int)Math.Floor(((float.Parse(temp[2]) / 4 * 20000))); motion_z.Add(new Point3D(x, y, z)); } modelPosition.X = (float)(motion_z[i].X); modelPosition.Y = (float)(motion_z[i].Y); modelPosition.Z = (float)(motion_z[i].Z); i++; } //Console.WriteLine("modelposX:" + modelPosition.X + "," + "motionzX:" + motion_z[i].X); }

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• Relationship between SOA and OOA

  - by TheSilverBullet

  Thomas Erl defines SOA as follows in his site: Service-oriented computing represents a new generation distributed computing platform. As such, it encompasses many things, including its own design paradigm and design principles, design pattern catalogs, pattern languages, a distinct architectural model, and related concepts, technologies, and frameworks. This definitely sounds like a whole new category which is parallel to object orientation. Almost one in which you would expect an entirely new language to exist for. Like procedural C and object oriented C#. Here is my understanding: In real life, we don't have entirely new language for SOA. And most application which have SOA architecture have an object oriented design underneath it. SOA is a "strategy" to make the entire application/service distributed and reliable. SOA needs OOPS working underneath it. Is this correct? Where does SOA (if at all it does) fit in with object oriented programming practices? Edit: I have learnt through answers that OOA and SOA work with each other and cannot be compared (in a "which is better" way). I have changed the title to "Relationship between SOA and OOA" rather than "comparison".

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• How to move an object along a circumference of another object?

  - by Lumis

  I am so out of math that it hurts, but for some of you this should be a piece of cake. I want to move an object around another along its ages or circumference on a simple circular path. At the moment my game algorithm knows how to move and position a sprite just at the edge of an obstacle and now it waits for the next point to move depending on various conditions. So the mathematical problem here is how to get (aX, aY) and (bX, bY) positions, when I know the Centre (cX, cY), the object position (oX, oY) and the distance required to move (d)

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• Design in "mixed" languages: object oriented design or functional programming?

  - by dema80

  In the past few years, the languages I like to use are becoming more and more "functional". I now use languages that are a sort of "hybrid": C#, F#, Scala. I like to design my application using classes that correspond to the domain objects, and use functional features where this makes coding easier, more coincise and safer (especially when operating on collections or when passing functions). However the two worlds "clash" when coming to design patterns. The specific example I faced recently is the Observer pattern. I want a producer to notify some other code (the "consumers/observers", say a DB storage, a logger, and so on) when an item is created or changed. I initially did it "functionally" like this: producer.foo(item => { updateItemInDb(item); insertLog(item) }) // calls the function passed as argument as an item is processed But I'm now wondering if I should use a more "OO" approach: interface IItemObserver { onNotify(Item) } class DBObserver : IItemObserver ... class LogObserver: IItemObserver ... producer.addObserver(new DBObserver) producer.addObserver(new LogObserver) producer.foo() //calls observer in a loop Which are the pro and con of the two approach? I once heard a FP guru say that design patterns are there only because of the limitations of the language, and that's why there are so few in functional languages. Maybe this could be an example of it? EDIT: In my particular scenario I don't need it, but.. how would you implement removal and addition of "observers" in the functional way? (I.e. how would you implement all the functionalities in the pattern?) Just passing a new function, for example?

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• Seperation of drawing and logic in games

  - by BFree

  I'm a developer that's just now starting to mess around with game development. I'm a .Net guy, so I've messed with XNA and am now playing around with Cocos2d for the iPhone. My question really is more general though. Let's say I'm building a simple Pong game. I'd have a Ball class and a Paddle class. Coming from the business world development, my first instinct is to not have any drawing or input handling code in either of these classes. //pseudo code class Ball { Vector2D position; Vector2D velocity; Color color; void Move(){} } Nothing in the ball class handles input, or deals with drawing. I'd then have another class, my Game class, or my Scene.m (in Cocos2D) which would new up the Ball, and during the game loop, it would manipulate the ball as needed. The thing is though, in many tutorials for both XNA and Cocos2D, I see a pattern like this: //pseudo code class Ball : SomeUpdatableComponent { Vector2D position; Vector2D velocity; Color color; void Update(){} void Draw(){} void HandleInput(){} } My question is, is this right? Is this the pattern that people use in game development? It somehow goes against everything I'm used to, to have my Ball class do everything. Furthermore, in this second example, where my Ball knows how to move around, how would I handle collision detection with the Paddle? Would the Ball need to have knowledge of the Paddle? In my first example, the Game class would have references to both the Ball and the Paddle, and then ship both of those off to some CollisionDetection manager or something, but how do I deal with the complexity of various components, if each individual component does everything themselves? (I hope I'm making sense.....)

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• What Is The Formula for the 3 of 9 Bar Code Alphabet?

  - by Chris Moschini

  Background: 3 of 9 Barcode Alphabet A simple syntax for 3 of 9 bar codes What is the formula behind the alphabet and digits in a 3 of 9 bar code? For example, ASCII has a relatively clear arrangement. Numbers start at 33, capitals at 65, lowercase at 97. From these starting points you can infer the ASCII code for any number or letter. The start point for each range is also a multiple of 32 + 1. Bar codes seem random and lacking sequence. If we use the syntax from the second link, this is the first six characters in 3 of 9: A 100-01 B 010-01 C 110-00 D 001-01 E 101-00 F 011-00 I see no pattern here; what is it? I'm as much interested in the designer's intended pattern behind these as I am in someone devising an algorithm of their own that can give you the above code for a given character based on its sequence. I struggled with where to put this question; is it history, computer science, information science? I chose Programmers because a StackExchange search had the most barcode hits here, and because I wanted to specifically relate it to ASCII to explain what sort of formula/explanation I'm looking for.

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• Use decorator and factory together to extend objects?

  - by TheClue

  I'm new to OOP and design pattern. I've a simple app that handles the generation of Tables, Columns (that belong to Table), Rows (that belong to Column) and Values (that belong to Rows). Each of these object can have a collection of Property, which is in turn defined as an enum. They are all interfaces: I used factories to get concrete instances of these products, depending on circumnstances. Now I'm facing the problem of extending these classes. Let's say I need another product called "SpecialTable" which in turn has some special properties or new methods like 'getSomethingSpecial' or an extended set of Property. The only way is to extend/specialize all my elements (ie. build a SpecialTableFactory, a SpecialTable interface and a SpecialTableImpl concrete)? What to do if, let's say, I plan to use standard methods like addRow(Column column, String name) that doesn't need to be specialized? I don't like the idea to inherit factories and interfaces, but since SpecialTable has more methods than Table i guess it cannot share the same factory. Am I wrong? Another question: if I need to define product properties at run time (a Table that is upgraded to SpecialTable at runtime), i guess i should use a decorator. Is it possible (and how) to combine both factory and decorator design? Is it better to use a State or Strategy pattern, instead?

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• Installing multi-boot Linux system

  - by user94924

  I have a dual (XP/Linux) boot Compaq Presario S4500UK with a couple of spare partitions on the boot drive which I want to use for testing different Linux distros/configs before installing them on "live" machines. I tried this with Oneiric which worked fine until I came to uninstalling the test system. Fortunately Oneiric uses Grub2 and so redirecting the bootloader to work from the original Linux partition was a piece of cake - if a bit annoying. I now need to do some tests on Hardy and DSL (Damned Small Linux), neither of which use Grub2. Question: Is it possible to install a test operating system without adding/replacing the bootloader (ie so I can still use Grub2 from the original partition with its nice interface and recovery facilities)? Is there another way of uninstalling/decommisioning a test OS which doesn't trash the boot loader? (The only way I know to do this is by deleting/reformatting the partition which takes with it the bootloader which is in that partition). Any help would be much appreciated. Tks jg1

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• Simplifying data search using .NET

  - by Peter

  An example on the asp.net site has an example of using Linq to create a search feature on a Music album site using MVC. The code looks like this - public ActionResult Index(string movieGenre, string searchString) { var GenreLst = new List<string>(); var GenreQry = from d in db.Movies orderby d.Genre select d.Genre; GenreLst.AddRange(GenreQry.Distinct()); ViewBag.movieGenre = new SelectList(GenreLst); var movies = from m in db.Movies select m; if (!String.IsNullOrEmpty(searchString)) { movies = movies.Where(s => s.Title.Contains(searchString)); } if (!string.IsNullOrEmpty(movieGenre)) { movies = movies.Where(x => x.Genre == movieGenre); } return View(movies); } I have seen similar examples in other tutorials and I have tried them in a real-world business app that I develop/maintain. In practice this pattern doesn't seem to scale well because as the search criteria expands I keep adding more and more conditions which looks and feels unpleasant/repetitive. How can I refactor this pattern? One idea I have is to create a column in every table that is "searchable" which could be a computed column that concatenates all the data from the different columns (SQL Server 2008). So instead of having movie genre and title it would be something like. if (!String.IsNullOrEmpty(searchString)) { movies = movies.Where(s => s.SearchColumn.Contains(searchString)); } What are the performance/design/architecture implications of doing this? I have also tried using procedures that use dynamic queries but then I have just moved the ugliness to the database. E.g. CREATE PROCEDURE [dbo].[search_music] @title as varchar(50), @genre as varchar(50) AS -- set the variables to null if they are empty IF @title = '' SET @title = null IF @genre = '' SET @genre = null SELECT m.* FROM view_Music as m WHERE (title = @title OR @title IS NULL) AND (genre LIKE '%' + @genre + '%' OR @genre IS NULL) ORDER BY Id desc OPTION (RECOMPILE) Any suggestions? Tips?

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• Has the emerging generation of programmers got the wrong idea about design patterns? [closed]

  - by MattDavey

  Over the years I've noticed a shift in attitude towards design patterns, particularly amongst the emerging generation of developers. There seems to be a notion these days that design patterns are silver bullets that instantly cure any problem, a proliferating idea that advancing as a software engineer simply means learning and applying more and more patterns. When confronted with a problem, developers no longer strive to truly understand the issue and design a solution - instead they simply pick a design pattern which seems to be a close fit, and try to brute-force it. You can see evidence of this by the many, many questions on Stack Overflow that begin with the phrase "what pattern should I use to...". I fall into a slightly more mature category of developers (5-10 years experience) and I have a very different viewpoint on patterns - simply as a communication tool to enhance clarity. I find this perspective of design patterns being lego bricks (collected like pokemon cards) a little disconcerting. Will developers lose this attitude as they gain more experience in software engineering? Or could these notions perhaps steer the direction of our craft in years to come? Did the older generation of developers have any similar concerns about us? (perhaps about OO design or similar...). if so, how did we turn out?

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• how to speed up this code? [migrated]

  - by dot

  I have some code that's taking over 3 seconds to complete. I'm just wondering if there's a faster way to do this. I have a string with anywhere from 10 to 70 rows of data. I break it up into an array and then loop through the array to find specific patterns. $this->_data = str_replace(chr(27)," ",$this->_data,$count);//strip out esc character $this->_data = explode("\r\n", $this->_data); $detailsArray = array(); foreach ($this->_data as $details) { $pattern = '/(\s+)([0-9a-z]*)(\s+)(100\/1000T|10|1000SX|\s+)(\s*)(\|)(\s+)(\w+)(\s+)(\w+)(\s+)(\w+)(\s+)(1000FDx|10HDx|100HDx|10FDx|100FDx|\s+)(\s*)(\w+)(\s*)(\w+|\s+)(\s*)(0)/i'; if (preg_match($pattern, $details, $matches)) { array_push($detailsArray, array( 'Port' => $matches[2], 'Type' => $matches[4], 'Alert' => $matches[8], 'Enabled' => $matches[10], 'Status' => $matches[12], 'Mode' => $matches[14], 'MDIMode' => $matches[16], 'FlowCtrl' => $matches[18], 'BcastLimit' => $matches[20])); }//end if }//end for $this->_data = $detailsArray; Just wondering if you think there's a way to make it more efficient. Thanks.

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• Spring Security Configuration Leads to Perpetual Authentication Request

  - by Sammy

  Hello, I have configured my web application with the following config file: <beans xmlns="http://www.springframework.org/schema/beans" xmlns:security="http://www.springframework.org/schema/security" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-3.0.xsd"> <security:global-method-security secured-annotations="enabled" pre-post-annotations="enabled" /> <!-- Filter chain; this is referred to from the web.xml file. Each filter is defined and configured as a bean later on. --> <!-- Note: anonumousProcessingFilter removed. --> <bean id="filterChainProxy" class="org.springframework.security.web.FilterChainProxy"> <security:filter-chain-map path-type="ant"> <security:filter-chain pattern="/**" filters="securityContextPersistenceFilter, basicAuthenticationFilter, exceptionTranslationFilter, filterSecurityInterceptor" /> </security:filter-chain-map> </bean> <!-- This filter is responsible for session management, or rather the lack thereof. --> <bean id="securityContextPersistenceFilter" class="org.springframework.security.web.context.SecurityContextPersistenceFilter"> <property name="securityContextRepository"> <bean class="org.springframework.security.web.context.HttpSessionSecurityContextRepository"> <property name="allowSessionCreation" value="false" /> </bean> </property> </bean> <!-- Basic authentication filter. --> <bean id="basicAuthenticationFilter" class="org.springframework.security.web.authentication.www.BasicAuthenticationFilter"> <property name="authenticationManager" ref="authenticationManager" /> <property name="authenticationEntryPoint" ref="authenticationEntryPoint" /> </bean> <!-- Basic authentication entry point. --> <bean id="authenticationEntryPoint" class="org.springframework.security.web.authentication.www.BasicAuthenticationEntryPoint"> <property name="realmName" value="Ayudo Web Service" /> </bean> <!-- An anonymous authentication filter, which is chained after the normal authentication mechanisms and automatically adds an AnonymousAuthenticationToken to the SecurityContextHolder if there is no existing Authentication held there. --> <!-- <bean id="anonymousProcessingFilter" class="org.springframework.security.web.authentication.AnonymousProcessingFilter"> <property name="key" value="ayudo" /> <property name="userAttribute" value="anonymousUser, ROLE_ANONYMOUS" /> </bean> --> <!-- Authentication manager that chains our main authentication provider and anonymous authentication provider. --> <bean id="authenticationManager" class="org.springframework.security.authentication.ProviderManager"> <property name="providers"> <list> <ref local="daoAuthenticationProvider" /> <ref local="inMemoryAuthenticationProvider" /> <!-- <ref local="anonymousAuthenticationProvider" /> --> </list> </property> </bean> <!-- Main authentication provider; in this case, memory implementation. --> <bean id="inMemoryAuthenticationProvider" class="org.springframework.security.authentication.dao.DaoAuthenticationProvider"> <property name="userDetailsService" ref="propertiesUserDetails" /> </bean> <security:user-service id="propertiesUserDetails" properties="classpath:operators.properties" /> <!-- Main authentication provider. --> <bean id="daoAuthenticationProvider" class="org.springframework.security.authentication.dao.DaoAuthenticationProvider"> <property name="userDetailsService" ref="userDetailsService" /> </bean> <!-- An anonymous authentication provider which is chained into the ProviderManager so that AnonymousAuthenticationTokens are accepted. --> <!-- <bean id="anonymousAuthenticationProvider" class="org.springframework.security.authentication.AnonymousAuthenticationProvider"> <property name="key" value="ayudo" /> </bean> --> <bean id="userDetailsService" class="org.springframework.security.core.userdetails.jdbc.JdbcDaoImpl"> <property name="dataSource" ref="dataSource" /> </bean> <bean id="exceptionTranslationFilter" class="org.springframework.security.web.access.ExceptionTranslationFilter"> <property name="authenticationEntryPoint" ref="authenticationEntryPoint" /> <property name="accessDeniedHandler"> <bean class="org.springframework.security.web.access.AccessDeniedHandlerImpl" /> </property> </bean> <bean id="filterSecurityInterceptor" class="org.springframework.security.web.access.intercept.FilterSecurityInterceptor"> <property name="securityMetadataSource"> <security:filter-security-metadata-source use-expressions="true"> <security:intercept-url pattern="/*.html" access="permitAll" /> <security:intercept-url pattern="/version" access="permitAll" /> <security:intercept-url pattern="/users/activate" access="permitAll" /> <security:intercept-url pattern="/**" access="isAuthenticated()" /> </security:filter-security-metadata-source> </property> <property name="authenticationManager" ref="authenticationManager" /> <property name="accessDecisionManager" ref="accessDecisionManager" /> </bean> <bean id="accessDecisionManager" class="org.springframework.security.access.vote.AffirmativeBased"> <property name="decisionVoters"> <list> <bean class="org.springframework.security.access.vote.RoleVoter" /> <bean class="org.springframework.security.web.access.expression.WebExpressionVoter" /> </list> </property> </bean> As soon as I run my application on tomcat, I get a request for username/password basic authentication dialog. Even when I try to access: localhost:8080/myapp/version, which is explicitly set to permitAll, I get the authentication request dialog. Help! Thank, Sammy

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• Spring security - Reach users ID without passing it through every controller

  - by nilsi

  I have a design issue that I don't know how to solve. I'm using Spring 3.2.4 and Spring security 3.1.4. I have a Account table in my database that looks like this: create table Account (id identity, username varchar unique, password varchar not null, firstName varchar not null, lastName varchar not null, university varchar not null, primary key (id)); Until recently my username was just only a username but I changed it to be the email address instead since many users want to login with that instead. I have a header that I include on all my pages which got a link to the users profile like this: <a href="/project/users/<%= request.getUserPrincipal().getName()%>" class="navbar-link"><strong><%= request.getUserPrincipal().getName()%></strong></a> The problem is that <%= request.getUserPrincipal().getName()%> returns the email now, I don't want to link the user's with thier emails. Instead I want to use the id every user have to link to the profile. How do I reach the users id's from every page? I have been thinking of two solutions but I'm not sure: Change the principal to contain the id as well, don't know how to do this and having problem finding good information on the topic. Add a model attribute to all my controllers that contain the whole user but this would be really ugly, like this. Account account = entityManager.find(Account.class, email); model.addAttribute("account", account); There are more way's as well and I have no clue which one is to prefer. I hope it's clear enough and thank you for any help on this. ====== Edit according to answer ======= I edited Account to implement UserDetails, it now looks like this (will fix the auto generated stuff later): @Entity @Table(name="Account") public class Account implements UserDetails { @Id private int id; private String username; private String password; private String firstName; private String lastName; @ManyToOne private University university; public Account() { } public Account(String username, String password, String firstName, String lastName, University university) { this.username = username; this.password = password; this.firstName = firstName; this.lastName = lastName; this.university = university; } public String getUsername() { return username; } public String getPassword() { return password; } public String getFirstName() { return firstName; } public String getLastName() { return lastName; } public void setUsername(String username) { this.username = username; } public void setPassword(String password) { this.password = password; } public void setFirstName(String firstName) { this.firstName = firstName; } public void setLastName(String lastName) { this.lastName = lastName; } public University getUniversity() { return university; } public void setUniversity(University university) { this.university = university; } public int getId() { return id; } public void setId(int id) { this.id = id; } @Override public Collection<? extends GrantedAuthority> getAuthorities() { // TODO Auto-generated method stub return null; } @Override public boolean isAccountNonExpired() { // TODO Auto-generated method stub return false; } @Override public boolean isAccountNonLocked() { // TODO Auto-generated method stub return false; } @Override public boolean isCredentialsNonExpired() { // TODO Auto-generated method stub return false; } @Override public boolean isEnabled() { // TODO Auto-generated method stub return true; } } I also added <%@ taglib prefix="sec" uri="http://www.springframework.org/security/tags" %> To my jsp files and trying to reach the id by <sec:authentication property="principal.id" /> This gives me the following org.springframework.beans.NotReadablePropertyException: Invalid property 'principal.id' of bean class [org.springframework.security.authentication.UsernamePasswordAuthenticationToken]: Bean property 'principal.id' is not readable or has an invalid getter method: Does the return type of the getter match the parameter type of the setter? ====== Edit 2 according to answer ======= I based my application on spring social samples and I never had to change anything until now. This are the files I think are relevant, please tell me if theres something you need to see besides this. AccountRepository.java public interface AccountRepository { void createAccount(Account account) throws UsernameAlreadyInUseException; Account findAccountByUsername(String username); } JdbcAccountRepository.java @Repository public class JdbcAccountRepository implements AccountRepository { private final JdbcTemplate jdbcTemplate; private final PasswordEncoder passwordEncoder; @Inject public JdbcAccountRepository(JdbcTemplate jdbcTemplate, PasswordEncoder passwordEncoder) { this.jdbcTemplate = jdbcTemplate; this.passwordEncoder = passwordEncoder; } @Transactional public void createAccount(Account user) throws UsernameAlreadyInUseException { try { jdbcTemplate.update( "insert into Account (firstName, lastName, username, university, password) values (?, ?, ?, ?, ?)", user.getFirstName(), user.getLastName(), user.getUsername(), user.getUniversity(), passwordEncoder.encode(user.getPassword())); } catch (DuplicateKeyException e) { throw new UsernameAlreadyInUseException(user.getUsername()); } } public Account findAccountByUsername(String username) { return jdbcTemplate.queryForObject("select username, firstName, lastName, university from Account where username = ?", new RowMapper<Account>() { public Account mapRow(ResultSet rs, int rowNum) throws SQLException { return new Account(rs.getString("username"), null, rs.getString("firstName"), rs.getString("lastName"), new University("test")); } }, username); } } security.xml <?xml version="1.0" encoding="UTF-8"?> <beans:beans xmlns="http://www.springframework.org/schema/security" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:beans="http://www.springframework.org/schema/beans" xsi:schemaLocation="http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-3.1.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd"> <http pattern="/resources/**" security="none" /> <http pattern="/project/" security="none" /> <http use-expressions="true"> <!-- Authentication policy --> <form-login login-page="/signin" login-processing-url="/signin/authenticate" authentication-failure-url="/signin?error=bad_credentials" /> <logout logout-url="/signout" delete-cookies="JSESSIONID" /> <intercept-url pattern="/addcourse" access="isAuthenticated()" /> <intercept-url pattern="/courses/**/**/edit" access="isAuthenticated()" /> <intercept-url pattern="/users/**/edit" access="isAuthenticated()" /> </http> <authentication-manager alias="authenticationManager"> <authentication-provider> <password-encoder ref="passwordEncoder" /> <jdbc-user-service data-source-ref="dataSource" users-by-username-query="select username, password, true from Account where username = ?" authorities-by-username-query="select username, 'ROLE_USER' from Account where username = ?"/> </authentication-provider> <authentication-provider> <user-service> <user name="admin" password="admin" authorities="ROLE_USER, ROLE_ADMIN" /> </user-service> </authentication-provider> </authentication-manager> </beans:beans> And this is my try of implementing a UserDetailsService public class RepositoryUserDetailsService implements UserDetailsService { private final AccountRepository accountRepository; @Autowired public RepositoryUserDetailsService(AccountRepository repository) { this.accountRepository = repository; } @Override public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException { Account user = accountRepository.findAccountByUsername(username); if (user == null) { throw new UsernameNotFoundException("No user found with username: " + username); } return user; } } Still gives me the same error, do I need to add the UserDetailsService somewhere? This is starting to be something else compared to my initial question, I should maybe start another question. Sorry for my lack of experience in this. I have to read up.

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• SQL SERVER – Database Dynamic Caching by Automatic SQL Server Performance Acceleration

  - by pinaldave

  My second look at SafePeak’s new version (2.1) revealed to me few additional interesting features. For those of you who hadn’t read my previous reviews SafePeak and not familiar with it, here is a quick brief: SafePeak is in business of accelerating performance of SQL Server applications, as well as their scalability, without making code changes to the applications or to the databases. SafePeak performs database dynamic caching, by caching in memory result sets of queries and stored procedures while keeping all those cache correct and up to date. Cached queries are retrieved from the SafePeak RAM in microsecond speed and not send to the SQL Server. The application gets much faster results (100-500 micro seconds), the load on the SQL Server is reduced (less CPU and IO) and the application or the infrastructure gets better scalability. SafePeak solution is hosted either within your cloud servers, hosted servers or your enterprise servers, as part of the application architecture. Connection of the application is done via change of connection strings or adding reroute line in the c:\windows\system32\drivers\etc\hosts file on all application servers. For those who would like to learn more on SafePeak architecture and how it works, I suggest to read this vendor’s webpage: SafePeak Architecture. More interesting new features in SafePeak 2.1 In my previous review of SafePeak new I covered the first 4 things I noticed in the new SafePeak (check out my article “SQLAuthority News – SafePeak Releases a Major Update: SafePeak version 2.1 for SQL Server Performance Acceleration”): Cache setup and fine-tuning – a critical part for getting good caching results Database templates Choosing which database to cache Monitoring and analysis options by SafePeak Since then I had a chance to play with SafePeak some more and here is what I found. 5. Analysis of SQL Performance (present and history): In SafePeak v.2.1 the tools for understanding of performance became more comprehensive. Every 15 minutes SafePeak creates and updates various performance statistics. Each query (or a procedure execute) that arrives to SafePeak gets a SQL pattern, and after it is used again there are statistics for such pattern. An important part of this product is that it understands the dependencies of every pattern (list of tables, views, user defined functions and procs). From this understanding SafePeak creates important analysis information on performance of every object: response time from the database, response time from SafePeak cache, average response time, percent of traffic and break down of behavior. One of the interesting things this behavior column shows is how often the object is actually pdated. The break down analysis allows knowing the above information for: queries and procedures, tables, views, databases and even instances level. The data is show now on all arriving queries, both read queries (that can be cached), but also any types of updates like DMLs, DDLs, DCLs, and even session settings queries. The stats are being updated every 15 minutes and SafePeak dashboard allows going back in time and investigating what happened within any time frame. 6. Logon trigger, for making sure nothing corrupts SafePeak cache data If you have an application with many parts, many servers many possible locations that can actually update the database, or the SQL Server is accessible to many DBAs or software engineers, each can access some database directly and do some changes without going thru SafePeak – this can create a potential corruption of the data stored in SafePeak cache. To make sure SafePeak cache is correct it needs to get all updates to arrive to SafePeak, and if a DBA will access the database directly and do some changes, for example, then SafePeak will simply not know about it and will not clean SafePeak cache. In the new version, SafePeak brought a new feature called “Logon Trigger” to solve the above challenge. By special click of a button SafePeak can deploy a special server logon trigger (with a CLR object) on your SQL Server that actually monitors all connections and informs SafePeak on any connection that is coming not from SafePeak. In SafePeak dashboard there is an interface that allows to control which logins can be ignored based on login names and IPs, while the rest will invoke cache cleanup of SafePeak and actually locks SafePeak cache until this connection will not be closed. Important to note, that this does not interrupt any logins, only informs SafePeak on such connection. On the Dashboard screen in SafePeak you will be able to see those connections and then decide what to do with them. Configuration of this feature in SafePeak dashboard can be done here: Settings -> SQL instances management -> click on instance -> Logon Trigger tab. Other features: 7. User management ability to grant permissions to someone without changing its configuration and only use SafePeak as performance analysis tool. 8. Better reports for analysis of performance using 15 minute resolution charts. 9. Caching of client cursors 10. Support for IPv6 Summary SafePeak is a great SQL Server performance acceleration solution for users who want immediate results for sites with performance, scalability and peak spikes challenges. Especially if your apps are packaged or 3rd party, since no code changes are done. SafePeak can significantly increase response times, by reducing network roundtrip to the database, decreasing CPU resource usage, eliminating I/O and storage access. SafePeak team provides a free fully functional trial www.safepeak.com/download and actually provides a one-on-one assistance during such trial. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: About Me, Pinal Dave, PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, SQL Utility, T SQL, Technology

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• Windows Azure Use Case: Hybrid Applications

  - by BuckWoody

  This is one in a series of posts on when and where to use a distributed architecture design in your organization's computing needs. You can find the main post here: http://blogs.msdn.com/b/buckwoody/archive/2011/01/18/windows-azure-and-sql-azure-use-cases.aspx  Description: Organizations see the need for computing infrastructures that they can “rent” or pay for only when they need them. They also understand the benefits of distributed computing, but do not want to create this infrastructure themselves. However, they may have considerations that prevent them from moving all of their current IT investment to a distributed environment: Private data (do not want to send or store sensitive data off-site) High dollar investment in current infrastructure Applications currently running well, but may need additional periodic capacity Current applications not designed in a stateless fashion In these situations, a “hybrid” approach works best. In fact, with Windows Azure, a hybrid approach is an optimal way to implement distributed computing even when the stipulations above do not apply. Keeping a majority of the computing function in an organization local while exploring and expanding that footprint into Windows and SQL Azure is a good migration or expansion strategy. A “hybrid” architecture merely means that part of a computing cycle is shared between two architectures. For instance, some level of computing might be done in a Windows Azure web-based application, while the data is stored locally at the organization. Implementation: There are multiple methods for implementing a hybrid architecture, in a spectrum from very little interaction from the local infrastructure to Windows or SQL Azure. The patterns fall into two broad schemas, and even these can be mixed. 1. Client-Centric Hybrid Patterns In this pattern, programs are coded such that the client system sends queries or compute requests to multiple systems. The “client” in this case might be a web-based codeset actually stored on another system (which acts as a client, the user’s device serving as the presentation layer) or a compiled program. In either case, the code on the client requestor carries the burden of defining the layout of the requests. While this pattern is often the easiest to code, it’s the most brittle. Any change in the architecture must be reflected on each client, but this can be mitigated by using a centralized system as the client such as in the web scenario. 2. System-Centric Hybrid Patterns Another approach is to create a distributed architecture by turning on-site systems into “services” that can be called from Windows Azure using the service Bus or the Access Control Services (ACS) capabilities. Code calls from a series of in-process client application. In this pattern you move the “client” interface into the server application logic. If you do not wish to change the application itself, you can “layer” the results of the code return using a product (such as Microsoft BizTalk) that exposes a Web Services Definition Language (WSDL) endpoint to Windows Azure using the Application Fabric. In effect, this is similar to creating a Service Oriented Architecture (SOA) environment, and has the advantage of de-coupling your computing architecture. If each system offers a “service” of the results of some software processing, the operating system or platform becomes immaterial, assuming it adheres to a service contract. There are important considerations when you federate a system, whether to Windows or SQL Azure or any other distributed architecture. While these considerations are consistent with coding any application for distributed computing, they are especially important for a hybrid application. Connection resiliency - Applications on-premise normally have low-latency and good connection properties, something you’re not always guaranteed in a distributed and hybrid application. Whether a centralized client or a distributed one, the code should be able to handle extended retry logic. Authorization and Access - In a single authorization environment like a Active Directory domain, security is handled at a user-password level. In a distributed computing environment, you have more options. You can mitigate this with  using The Windows Azure Application Fabric feature of ACS to make the Azure application aware of the App Fabric as an ADFS provider. However, a claims-based authentication structure is often a superior choice.  Consistency and Concurrency - When you have a Relational Database Management System (RDBMS), Consistency and Concurrency are part of the design. In a Service Architecture, you need to plan for sequential message handling and lifecycle. Resources: How to Build a Hybrid On-Premise/In Cloud Application: http://blogs.msdn.com/b/ignitionshowcase/archive/2010/11/09/how-to-build-a-hybrid-on-premise-in-cloud-application.aspx  General Architecture guidance: http://blogs.msdn.com/b/buckwoody/archive/2010/12/21/windows-azure-learning-plan-architecture.aspx   

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• Cloud Computing Architecture Patterns: Don’t Focus on the Client

  - by BuckWoody

  Normally I try to put topics in the positive in other words "Do this" not "Don't do that". Sometimes its clearer to focus on what *not* to do. Popular development processes often start with screen mockups, or user input descriptions. In a scale-out pattern like Cloud Computing on Windows Azure, that's the wrong place to start. Start with the Data    Instead, I recommend that you start with the data that a process requires. That data might be temporary or persisted, but starting with the data and its requirements helps to define not only the storage engine you need but also drives everything from security to the integrity of the application. For instance, assume the requirements show that the user must enter their phone number, and that this datum is used in a contact management system further down the application chain. For that datum, you can determine what data type you need (U.S. only or International?) the security requirements, whether it needs ACID compliance, how it will be searched, indexed and so on. From one small data point you can extrapolate out your options for storing and processing the data. Here's the interesting part, which begins to break the patterns that we've used for decades: all of the data doesn't have the same requirements. The phone number might be best suited for a list, or an element, or a string, with either BASE or ACID requirements, based on how it is used. That means we don't have to dump everything into XML, an RDBMS, a NoSQL engine, or a flat file exclusively. In fact, one record might use all of those depending on the use-case requirements. Next Is Data Management  With the data defined, we can move on to how to store the data. Again, the requirements now dictate whether we need a full relational calculus or set-based operations, or we can choose another method based on the requirements for the data. And breaking another pattern its OK to store in more than once, in more than one location. We do this all the time for reporting systems and Business Intelligence systems, so this is a pattern we need to think about even for OLTP data. Move to Data Transport How does the data get around? We can use a connection-based method, sending the data along a transport to the storage engine, but in some cases we may want to use a cache, a queue, the Service Bus, or Complex Event Processing. Finally, Data Processing Most RDBMS engines, NoSQL, and certainly Big Data engines not only store data, but can process and manipulate it as well. Its doubtful that you'll calculate that phone number right? Well, if you're the phone company, you most certainly will. And so we see that even once we've chosen the data type, storage and engine, the same element can have different computing requirements based on how it is used. Sure, We Need A Front-End At Some Point Not all data is entered by human hands in fact most data isn't. We don't really need a Graphical User Interface (GUI) we need some way for a GUI to get data into and out of the systems listed earlier.   But when we do need to allow users to enter or examine data, that should be left to the GUI that best fits the device the user has. Ever tried to use an application designed for a web browser on a phone? Or one designed for a tablet on a phone? Its usually quite painful. The siren song of "We'll just write one interface for all devices" is strong, and has beguiled many an unsuspecting architect. But they just don't work out.   Instead, focus on the data, its transport and processing. Create API calls or a message system that allows for resilient transport to the device or interface, and let it do what it does best. References Microsoft Architecture Journal:   http://msdn.microsoft.com/en-us/architecture/bb410935.aspx Patterns and Practices:   http://msdn.microsoft.com/en-us/library/ff921345.aspx Windows Azure iOS, Android, Windows 8 Mobile Devices SDK: http://www.windowsazure.com/en-us/develop/mobile/tutorials/get-started-ios/ Windows Azure Facebook SDK: http://ntotten.com/2013/03/14/using-windows-azure-mobile-services-with-the-facebook-sdk-for-windows-phone/

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• Delving into design patterns, and what that means for the Oracle user experience

  - by Kathy.Miedema

  By Kathy Miedema, Oracle Applications User Experience George Hackman, Senior Director, Applications User Experiences The Oracle Applications User Experience team has some exciting things happening around Fusion Applications design patterns. Because we’re hoping to have some new offerings soon (stay tuned with VoX to see what’s in the pipeline around Fusion Applications design patterns), now is a good time to talk more about what design patterns can do for the individual user as well as the entire company. George Hackman, Senior Director of Operations User Experience, says the first thing to note is that user experience is not just about the user interface. It’s about understanding how people do things, observing them, and then finding the patterns that emerge. The Applications UX team develops those patterns and then builds them into Oracle applications. What emerges, Hackman says, is a consistent, efficient user experience that promotes a productive workplace. Creating design patterns What is a design pattern in the context of enterprise software? “Every day, people use technology to get things done,” Hackman says. “They navigate a virtual world that reaches from enterprise to consumer apps, and from desktop to mobile. This virtual world is constantly under construction. New areas are being developed and old areas are being redone. As this world is being built and remodeled, efficient pathways and practices emerge. “Oracle's user experience team watches users navigate this world. We measure their productivity and ask them about their satisfaction. We take the most efficient, most productive pathways from the enterprise and consumer world and turn them into Oracle's user experience patterns.” Hackman describes the process as combining all of the best practices from every part of a user’s world. Members of the user experience team observe, analyze, design, prototype, and measure each work task to find the best possible pattern for a particular work flow. As the team builds the patterns, “we make sure they are fully buildable using Oracle technology,” Hackman said. “So customers know they can use these patterns. There’s no need to make something up from scratch, not knowing whether you can even build it.” Hackman says that creating something on a computer is a good example of a user experience pattern. “People are creating things all the time,” he says. “On the consumer side, they are creating documents. On the enterprise side, they are creating expense reports. On a mobile phone, they are creating contacts. They are using different apps like iPhone or Facebook or Gmail or Oracle software, all doing this creation process.” The Applications UX team starts their process by observing how people might create something. “We observe people creating things. We see the patterns, we analyze and document, then we apply them to our products. It might be different from phone to web browser, but we have these design patterns that create a consistent experience across platforms, and across products, too. The result for customers Oracle constantly improves its part of the virtual world, Hackman said. New products are created and existing products are upgraded. Because Oracle builds user experience design patterns, Oracle's virtual world becomes both more powerful and more familiar at the same time. Because of design patterns, users can navigate with ease as they embrace the latest technology – because it behaves the way they expect it to. This means less training and faster adoption for individual users, and more productivity for the business as a whole. Hackman said Oracle gives customers and partners access to design patterns so that they can build in the virtual world using the same best practices. Customers and partners can extend applications with a user experience that is comfortable and familiar to their users. For businesses that are integrating different Oracle applications, design patterns are key. The user experience created in E-Business Suite should be similar to the user experience in Fusion Applications, Hackman said. If a user is transitioning from one application to the other, it shouldn’t be difficult for them to do their work. With design patterns, it isn’t. “Oracle user experience patterns are the building blocks for the virtual world that ensure productivity, consistency and user satisfaction,” Hackman said. “They are built for the enterprise, but incorporate the best practices from across the virtual world. They empower productivity and facilitate social interaction. When you build with patterns, you get all the end-user benefits of less training / retraining from the finished product. You also get faster / cheaper development.” What’s coming? You can already access design patterns to help you build Dashboards with OBIEE here. And we promised you at the beginning that we had something in the pipeline on Fusion Applications design patterns. Look for the announcement about when they are available here on VoX.

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• How to make creating viewmodels at runtime less painful

  - by Mr Happy

  I apologize for the long question, it reads a bit as a rant, but I promise it's not! I've summarized my question(s) below In the MVC world, things are straightforward. The Model has state, the View shows the Model, and the Controller does stuff to/with the Model (basically), a controller has no state. To do stuff the Controller has some dependencies on web services, repository, the lot. When you instantiate a controller you care about supplying those dependencies, nothing else. When you execute an action (method on Controller), you use those dependencies to retrieve or update the Model or calling some other domain service. If there's any context, say like some user wants to see the details of a particular item, you pass the Id of that item as parameter to the Action. Nowhere in the Controller is there any reference to any state. So far so good. Enter MVVM. I love WPF, I love data binding. I love frameworks that make data binding to ViewModels even easier (using Caliburn Micro a.t.m.). I feel things are less straightforward in this world though. Let's do the exercise again: the Model has state, the View shows the ViewModel, and the ViewModel does stuff to/with the Model (basically), a ViewModel does have state! (to clarify; maybe it delegates all the properties to one or more Models, but that means it must have a reference to the model one way or another, which is state in itself) To do stuff the ViewModel has some dependencies on web services, repository, the lot. When you instantiate a ViewModel you care about supplying those dependencies, but also the state. And this, ladies and gentlemen, annoys me to no end. Whenever you need to instantiate a ProductDetailsViewModel from the ProductSearchViewModel (from which you called the ProductSearchWebService which in turn returned IEnumerable<ProductDTO>, everybody still with me?), you can do one of these things: call new ProductDetailsViewModel(productDTO, _shoppingCartWebService /* dependcy */);, this is bad, imagine 3 more dependencies, this means the ProductSearchViewModel needs to take on those dependencies as well. Also changing the constructor is painful. call _myInjectedProductDetailsViewModelFactory.Create().Initialize(productDTO);, the factory is just a Func, they are easily generated by most IoC frameworks. I think this is bad because Init methods are a leaky abstraction. You also can't use the readonly keyword for fields that are set in the Init method. I'm sure there are a few more reasons. call _myInjectedProductDetailsViewModelAbstractFactory.Create(productDTO); So... this is the pattern (abstract factory) that is usually recommended for this type of problem. I though it was genius since it satisfies my craving for static typing, until I actually started using it. The amount of boilerplate code is I think too much (you know, apart from the ridiculous variable names I get use). For each ViewModel that needs runtime parameters you'll get two extra files (factory interface and implementation), and you need to type the non-runtime dependencies like 4 extra times. And each time the dependencies change, you get to change it in the factory as well. It feels like I don't even use a DI container anymore. (I think Castle Windsor has some kind of solution for this [with it's own drawbacks, correct me if I'm wrong]). do something with anonymous types or dictionary. I like my static typing. So, yeah. Mixing state and behavior in this way creates a problem which don't exist at all in MVC. And I feel like there currently isn't a really adequate solution for this problem. Now I'd like to observe some things: People actually use MVVM. So they either don't care about all of the above, or they have some brilliant other solution. I haven't found an in-depth example of MVVM with WPF. For example, the NDDD-sample project immensely helped me understand some DDD concepts. I'd really like it if someone could point me in the direction of something similar for MVVM/WPF. Maybe I'm doing MVVM all wrong and I should turn my design upside down. Maybe I shouldn't have this problem at all. Well I know other people have asked the same question so I think I'm not the only one. To summarize Am I correct to conclude that having the ViewModel being an integration point for both state and behavior is the reason for some difficulties with the MVVM pattern as a whole? Is using the abstract factory pattern the only/best way to instantiate a ViewModel in a statically typed way? Is there something like an in depth reference implementation available? Is having a lot of ViewModels with both state/behavior a design smell?

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• MVVM - how to make creating viewmodels at runtime less painfull

  - by Mr Happy

  I apologize for the long question, it reads a bit as a rant, but I promise it's not! I've summarized my question(s) below In the MVC world, things are straightforward. The Model has state, the View shows the Model, and the Controller does stuff to/with the Model (basically), a controller has no state. To do stuff the Controller has some dependencies on web services, repository, the lot. When you instantiate a controller you care about supplying those dependencies, nothing else. When you execute an action (method on Controller), you use those dependencies to retrieve or update the Model or calling some other domain service. If there's any context, say like some user wants to see the details of a particular item, you pass the Id of that item as parameter to the Action. Nowhere in the Controller is there any reference to any state. So far so good. Enter MVVM. I love WPF, I love data binding. I love frameworks that make data binding to ViewModels even easier (using Caliburn Micro a.t.m.). I feel things are less straightforward in this world though. Let's do the exercise again: the Model has state, the View shows the ViewModel, and the ViewModel does stuff to/with the Model (basically), a ViewModel does have state! (to clarify; maybe it delegates all the properties to one or more Models, but that means it must have a reference to the model one way or another, which is state in itself) To do stuff the ViewModel has some dependencies on web services, repository, the lot. When you instantiate a ViewModel you care about supplying those dependencies, but also the state. And this, ladies and gentlemen, annoys me to no end. Whenever you need to instantiate a ProductDetailsViewModel from the ProductSearchViewModel (from which you called the ProductSearchWebService which in turn returned IEnumerable<ProductDTO>, everybody still with me?), you can do one of these things: call new ProductDetailsViewModel(productDTO, _shoppingCartWebService /* dependcy */);, this is bad, imagine 3 more dependencies, this means the ProductSearchViewModel needs to take on those dependencies as well. Also changing the constructor is painfull. call _myInjectedProductDetailsViewModelFactory.Create().Initialize(productDTO);, the factory is just a Func, they are easily generated by most IoC frameworks. I think this is bad because Init methods are a leaky abstraction. You also can't use the readonly keyword for fields that are set in the Init method. I'm sure there are a few more reasons. call _myInjectedProductDetailsViewModelAbstractFactory.Create(productDTO); So... this is the pattern (abstract factory) that is usually recommended for this type of problem. I though it was genious since it satisfies my craving for static typing, until I actually started using it. The amount of boilerplate code is I think too much (you know, apart from the ridiculous variable names I get use). For each ViewModel that needs runtime parameters you'll get two extra files (factory interface and implementation), and you need to type the non-runtime dependencies like 4 extra times. And each time the dependencies change, you get to change it in the factory as well. It feels like I don't even use an DI container anymore. (I think Castle Windsor has some kind of solution for this [with it's own drawbacks, correct me if I'm wrong]). do something with anonymous types or dictionary. I like my static typing. So, yeah. Mixing state and behavior in this way creates a problem which don't exist at all in MVC. And I feel like there currently isn't a really adequate solution for this problem. Now I'd like to observe some things: People actually use MVVM. So they either don't care about all of the above, or they have some brilliant other solution. I haven't found an indepth example of MVVM with WPF. For example, the NDDD-sample project immensely helped me understand some DDD concepts. I'd really like it if someone could point me in the direction of something similar for MVVM/WPF. Maybe I'm doing MVVM all wrong and I should turn my design upside down. Maybe I shouldn't have this problem at all. Well I know other people have asked the same question so I think I'm not the only one. To summarize Am I correct to conclude that having the ViewModel being an integration point for both state and behavior is the reason for some difficulties with the MVVM pattern as a whole? Is using the abstract factory pattern the only/best way to instantiate a ViewModel in a statically typed way? Is there something like an in depth reference implementation available? Is having a lot of ViewModels with both state/behavior a design smell?

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