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  • How to apply Data Oriented Design with Object Oriented Programming?

    - by Pombal
    I've read lots of articles about Data Oriented Design (DOD) and I understand it but I can't design an Object Oriented Programming (OOP) system with DOD in mind, I think my OOP education is blocking me. How should I think to mix the two? The objective is to have a nice OOP interface while using DOD behind the scenes. I saw this too but didn't help much: http://stackoverflow.com/questions/3872354/how-to-apply-dop-and-keep-a-nice-user-interface

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  • Change Tweetmeme button colour under wordpress

    - by Andrew Bolster
    I've had a poke around in the TweetMeme plugin code and IANA JS Guru, but I cant find any sensible way to make specific styling changes; you can add div-specific CSS characteristics, but I'm talking about changing the resting colour and the hover colour of the button. I've googled around and noone seems to have asked it on here so I thought I should. PS I would not be surprised by this question being migrated to SO, but since this is more of a design/use question rather than a programming question, I thought it was worth trying here first.

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  • What is UVIndex and how do I use it on OpenGL?

    - by Delta
    I am a noob in OpenGL ES 2.0 (for WebGL) and I'm trying to draw a simple model I've made with a 3D tool and exported to .fbx format. I've been able to draw some models that only have: A vertex buffer, a index buffer for the vertices, a normal buffer and a texture coordinate buffer, but this model now has a "UVIndex" and I'm not sure where am I supposed to put this UVIndex. My code looks like this: GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.VertexBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["vPosition"],3,GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.NormalBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["vNormal"], 3, GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.TexCoordBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["TexCoord"], 2, GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ELEMENT_ARRAY_BUFFER, this.Model.House.IndexBuffer); GL.bindTexture(GL.TEXTURE_2D, this.Texture.HTex1); GL.activeTexture(GL.TEXTURE0); GL.drawElements(GL.TRIANGLES, this.Model.House.IndexBuffer.Length, GL.UNSIGNED_SHORT, 0); But my model renders totally incorrect and I think it has to do with the fact that I am ignoring this "UVIndex" in the .fbx file, since I've never drawn any model that uses this UVIndex I really have no clue on what to do with it. This is the json file containing the model's data: http://pastebin.com/raw.php?i=G294TVmz

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  • Grid Style. Is It The Next Big Thing In Web Design?

    Inspired by typographic magazine layout grids more and more web designers are starting to embrace grid-based design siting cleaner and more easily digestible web pages as a benefit. The concept of ... [Author: Michiel Van Kets - Web Design and Development - June 17, 2010]

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  • Can DrawIndexedPrimitives() be used for drawing a loaded model mesh-wise?

    - by Afzal
    I am using DrawIndexedPrimitives() for drawing a loaded 3D model by drawing each mesh part, but this process makes my application very slow. This is perhaps because of a very large number of vertex/index buffer data created in video memory. That is why I am looking for a way to use the same method for each model mesh instead. The problem is that I don't know how I will set the textures of that mesh. Can anyone offer me some guidance?

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  • Journée consacrée aux approches "Model Driven" à Paris le 24 novembre, participation gratuite en présence d'experts de renom

    Journée consacrée aux approches "Model Driven" à Paris le 24 novembre Participation gratuite à une rencontre d'échange en présence d'experts de renom SoftFluent organise en compagnie d'autres sociétés spécialisées en développement logiciel la journée du Model Driven le 24 novembre 2011 à Paris - coeur défense. En présence d'experts reconnus du domaine, les visiteurs assisteront à des discussions et conférences autour des approches de fabrication de logiciels pilotées par les modèles : adhésion des utilisateurs, agilité, performances des applications, qualité du code produit, modernisation du SI, etc. À travers des conférences, démonstrations et retours d'expérienc...

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  • Are all View Models supposed to be accessed through the Main View Model in MVVM?

    - by chustar
    I am currently working on a WP8 application. My current design is to have each view bind against a specific view model directly. Looking through the samples though, it seems that another way is to have all the view models accessed through the Main View Model and then have all the views to their view models through the MVM. Is this the correct way to do it (So that it doesn't cause flexibility and other issues in the future)?

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  • Case studies for successful service (project) based software development businesses without constant overtime from its employees [closed]

    - by Ryan Taylor
    I work for an IT company that is primarily services (project) based rather than product based. All software engineers are salaried. The company has set new expectations that everyone should work 48 hours per week instead of 40. Note, this isn't occasional overtime due to crunches. This is the new 40. The reasoning is that this enables the company to provide benefits to its employees such as monetary incentives and training because the company is more profitable. more hours worked = more billable hours = larger profit I understand the need for profitability and the occasional crunch time and have put in the extra hours when it was needed and beneficial to the project. However, I am also very sensitive to work life balance and have raised my concerns about the the new expectation. My employer is open to other methods to increase profitability so I hold hope that we can turn things around before it becomes a horrible place to work. How does a services based company become more profitable without increasing the number of hours expected from it's salaried employees? Are there any case studies showing the pros and cons of consistent overtime? Are there any case studies for a successful service based business model (for software development companies) that does not require consistent overtime from its employees?

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  • How to model a system to help my team grasp the project's bigger picture? [closed]

    - by user1796528
    According to the software engineering point of view, I should model the system to make it easier for other people to understand well what they work on. To do so, I have used the Dia drawing program. But, after having used Dia for some time, I find that it falls short in helping me to correctly and efficiently model my project. How do you usually tackle this problem (modelling a project in the large) and what tools would you recommend for the job, and why?

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  • APress Deal of the Day 20/Dec/2010 - Beginning SQL Server Modeling: Model-Driven Application Development in SQL Server 2008

    - by TATWORTH
    Todays $10 bargain PDF from Apress is: Beginning SQL Server Modeling: Model-Driven Application Development in SQL Server 2008 Get ready for model-driven application development with SQL Server Modeling! This book covers Microsoft's SQL Server Modeling (formerly known under the code name "Oslo") in detail and contains the information you need to be successful with designing and implementing workflow modeling. $49.99 | Published Jul 2010 |

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  • Stairway to Transaction Log Management in SQL Server, Level 6: Managing the Log in BULK_LOGGED Recovery Model

    A DBA may consider switching a database to the BULK_LOGGED recovery model in the short term during, for example, bulk load operations. When a database is operating in the BULK_LOGGED model these, and a few other operations such as index rebuilds, can be minimally logged and will therefore use much less space in the log NEW! Never waste another weekend deployingDeploy SQL Server changes and ASP .NET applications fast, frequently, and without fuss, using Deployment Manager, the new tool from Red Gate. Try it now.

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  • Doctrine Build-All Task fails in NetBeans - Class not found! Fatal Error: call to evictAll()

    - by Prasad
    When I build my model with the symfony doctrine:build --all --and-load command I have made no major changes to the model/schema, this is something new. I also tried sub-commands like build-model, build-tables, but they all hang.. I'm trying this in net beans. Any clue what this is? This command will remove all data in the following "dev" connection(s): - doctrine Are you sure you want to proceed? (y/N) y >> doctrine Dropping "doctrine" database >> doctrine Creating "dev" environment "doctrine" database >> doctrine generating model classes >> file+ C:\Documents and Settings\Gupte...\Temp/doctrine_schema_69845.yml >> tokens D:/projects/cim/lib/model/doctrine/base/BaseAffiliate.class.php >> tokens D:/projects/cim/lib/model/doctrine/base/BaseContact.class.php >> tokens D:/projects/cim/lib/model/doctr...e/BaseContactLocation.class.php >> tokens D:/projects/cim/lib/model/doctr...se/BaseGroupAffiliate.class.php >> tokens D:/projects/cim/lib/model/doctrine/base/BaseGrouping.class.php >> tokens D:/projects/cim/lib/model/doctrine/base/BaseLocation.class.php >> tokens D:/projects/cim/lib/model/doctr.../base/BasePhonenumber.class.php >> tokens D:/projects/cim/lib/model/doctrine/base/BaseTenant.class.php >> tokens D:/projects/cim/lib/model/doctr...base/BasesfGuardGroup.class.php >> tokens D:/projects/cim/lib/model/doctr...fGuardGroupPermission.class.php >> tokens D:/projects/cim/lib/model/doctr...BasesfGuardPermission.class.php >> tokens D:/projects/cim/lib/model/doctr...asesfGuardRememberKey.class.php >> tokens D:/projects/cim/lib/model/doctr.../base/BasesfGuardUser.class.php >> tokens D:/projects/cim/lib/model/doctr.../BasesfGuardUserGroup.class.php >> tokens D:/projects/cim/lib/model/doctr...sfGuardUserPermission.class.php >> autoload Resetting application autoloaders >> file- D:/projects/cim/cache/frontend/.../config/config_autoload.yml.php >> file- D:/projects/cim/cache/backend/dev/config/config_autoload.yml.php >> doctrine generating form classes [?php /** * Contact form base class. * * @method Contact getObject() Returns the current form's model object * * @package ##PROJECT_NAME## * @subpackage form * @author ##AUTHOR_NAME## * @version SVN: $Id: sfDoctrineFormGeneratedTemplate.php 24171 2009-11-19 16:37:50Z Kris.Wallsmith $ */ abstract class BaseContactForm extends BaseFormDoctrine { public function setup() { $this->setWidgets(array( 'id' Fatal error: Call to a member function evictAll() on a non-object in D:\projects\cim\lib\vendor\symfony\lib\plugins\sfDoctrinePlugin\lib\vendor\doctrine\Doctrine\Connection.php on line 1239 Call Stack: 0.9552 322760 1. {main}() D:\projects\cim\symfony:0 0.9594 587208 2. include('D:\projects\cim\lib\vendor\symfony\lib\command\cli.php') D:\projects\cim\symfony:14 11.9775 17118936 3. sfDatabaseManager->shutdown() D:\projects\cim\lib\vendor\symfony\lib\database\sfDatabaseManager.class.php:0 11.9775 17118936 4. sfDoctrineDatabase->shutdown() D:\projects\cim\lib\vendor\symfony\lib\database\sfDatabaseManager.class.php:134 11.9775 17118936 5. Doctrine_Manager->closeConnection() D:\projects\cim\lib\vendor\symfony\lib\plugins\sfDoctrinePlugin\lib\database\sfDoctrineDatabase.class.php:165 11.9775 17118936 6. Doctrine_Connection->close() D:\projects\cim\lib\vendor\symfony\lib\plugins\sfDoctrinePlugin\lib\vendor\doctrine\Doctrine\Manager.php:579 11.9776 17120160 7. Doctrine_Connection->clear() D:\projects\cim\lib\vendor\symfony\lib\plugins\sfDoctrinePlugin\lib\vendor\doctrine\Doctrine\Connection.php:1268 Couldn't find class Similar thing is mentioned here: http://osdir.com/ml/symfony-users/2010-01/msg00642.html

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  • Which pattern should be used for editing properties with modal view controller on iPhone?

    - by Matthew Daugherty
    I am looking for a good pattern for performing basic property editing via a modal view on the iPhone. Assume I am putting together an application that works like the Contacts application. The "detail" view controller displays all of the contact's properties in a UITableView. When the UITableView goes into edit mode a disclosure icon is displayed in the cells. Clicking a cell causes a modal "editor" view controller to display a view that allows the user to modify the selected property. This view will often contain only a single text box or picker. The user clicks Cancel/Save and the "editor" view is dismissed and the "detail" view is updated. In this scenario, which view is responsible for updating the model? The "editor" view could update the property directly using Key-Value Coding. This appears in the CoreDataBooks example. This makes sense to me on some level because it treats the property as the model for the editor view controller. However, this is not the pattern suggested by the View Controller Programming Guide. It suggests that the "editor" view controller should define a protocol that the "detail" controller adopts. When the user indicates they are done with the edit, the "detail" view controller is called back with the entered value and it dismisses the "editor" view. Using this approach the "detail" controller updates the model. This approach seems problematic if you are using the same "editor" view for multiple properties since there is only a single call-back method. Would love to get some feedback on what approach works best.

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  • Business Logic Layer Pattern on Rails? MVCL

    - by Fabiano PS
    That is a broad question, and I appreciate no short/dumb asnwers like: "Oh that is the model job, this quest is retarded (period)" PROBLEM Where I work at people created a system over 2 years for managing the manufacture process over demand in the most simplified still broad as possible, involving selling, buying, assemble, The system is coded over Ruby On Rails. The app has been changed lots of times and the result is a mess on callbacks (some are called several times), 200+ models, and fat controllers: Total bad. The QUESTION is, if there is a gem, or pattern designed to handle Rails large app logic? The logic whould be able to fully talk to models (whose only concern would be data format handling and validation) What I EXPECT is to reduce complexity from various controllers, and hard to track callbacks into files with the responsibility to handle a business operation logic. In some cases there is the need to wait for a response, in others, only validation of the input is enough and a bg process would take place. ie: -- Sell some products (need to wait the operation to finish) 1. Set a View able to get the products input 2. Controller gets the product list inputed by employee and call the logic Logic::ExecuteWithResponse('sell', 'products', :prods => @product_list_with_qtt, :when => @date, :employee => current_user() ) This Logic would handle buying order, assemble order, machine schedule, warehouse reservation, and others. Have in mind that a callback on SalesOrder is not enough, since it depends on where it is called (no field for that), depends on the class of the user, among other stuff not visible for the model, or in some cases it would take long for the model to process.

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  • Should this even be a has_many :through association?

    - by GoodGets
    A Post belongs_to a User, and a User has_many Posts. A Post also belongs_to a Topic, and a Topic has_many Posts. class User < ActiveRecord::Base has_many :posts end class Topic < ActiveRecord::Base has_many :posts end class Post < ActiveRecord::Base belongs_to :user belongs_to :topic end Well, that's pretty simple and very easy to set up, but when I display a Topic, I not only want all of the Posts for that Topic, but also the user_name and the user_photo of the User that made that Post. However, those attributes are stored in the User model and not tied to the Topic. So how would I go about setting that up? Maybe it can already be called since the Post model has two foreign keys, one for the User and one for the Topic? Or, maybe this is some sort of "one-way" has_many through assiociation. Like the Post would be the join model, and a Topic would has_many :users, :through = :posts. But the reverse of this is not true. Like a User does NOT has_many :topics. So would this even need to be has_many :though association? I guess I'm just a little confused on what the controller would look like to call both the Post and the User of that Post for a give Topic. Edit: Seriously, thank you to all that weighed in. I chose tal's answer because I used his code for my controller; however, I could have just as easily chosen either j.'s or tim's instead. Thank you both as well. This was so damn simple to implement, and I think today marks the day that I'm beginning to fall in love with rails.

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  • Building a News-feed that comprises posts "created by user's connections" && "on the topics user is following"

    - by aklin81
    I am working on a project of Questions & Answers website that allows a user to follow questions on certain topics from his network. A user's news-feed wall comprises of only those questions that have been posted by his connections and tagged on the topics that he is following(his expertise topics). I am confused what database's datamodel would be most fitting for such an application. The project needs to consider the future provisions for scalability and high performance issues. I have been looking at Cassandra and MySQL solutions as of now. After my study of Cassandra I realized that Simple news-feed design that shows all the posts from network would be easy to design using Cassandra by executing fast writes to all followers of a user about the post from user. But for my kind of application where there is an additional filter of 'followed topics', (ie, the user receives posts "created by his network" && "on topics user is following"), I could not convince myself with a good schema design in Cassandra. I hope if I missed something because of my short understanding of cassandra, perhaps, can you please help me out with your suggestions of how this news-feed could be implemented in Cassandra ? Looking for a great project with Cassandra ! Edit: There are going to be maximum 5 tags allowed for tagging the question (ie, max 5 topics can be tagged on a question).

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  • Two objects with dependencies for each other. Is that bad?

    - by Kasper Grubbe
    Hi SO. I am learning a lot about design patterns these days. And I want to ask you about a design question that I can't find an answer to. Currently I am building a little Chat-server using sockets, with multiple Clients. Currently I have three classes. Person-class which holds information like nick, age and a Room-object. Room-class which holds information like room-name, topic and a list of Persons currently in that room. Hotel-class which have a list of Persons and a list of Rooms on the server. I have made a diagram to illustrate it (Sorry for the big size!): http://i.imgur.com/Kpq6V.png I have a list of players on the server in the Hotel-class because it would be nice to keep track of how many there are online right now (Without having to iterate through all of the rooms). The persons live in the Hotel-class because I would like to be able to search for a specific Person without searching the rooms. Is this bad design? Is there another way of achieve it? Thanks.

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  • Using Doctrine to abstract CRUD operations

    - by TomWilsonFL
    This has bothered me for quite a while, but now it is necessity that I find the answer. We are working on quite a large project using CodeIgniter plus Doctrine. Our application has a front end and also an admin area for the company to check/change/delete data. When we designed the front end, we simply consumed most of the Doctrine code right in the controller: //In semi-pseudocode function register() { $data = get_post_data(); if (count($data) && isValid($data)) { $U = new User(); $U->fromArray($data); $U->save(); $C = new Customer(); $C->fromArray($data); $C->user_id = $U->id; $C->save(); redirect_to_next_step(); } } Obviously when we went to do the admin views code duplication began and considering we were in a "get it DONE" mode so it now stinks with code bloat. I have moved a lot of functionality (business logic) into the model using model methods, but the basic CRUD does not fit there. I was going to attempt to place the CRUD into static methods, i.e. Customer::save($array) [would perform both insert and update depending on if prikey is present in array], Customer::delete($id), Customer::getObj($id = false) [if false, get all data]. This is going to become painful though for 32 model objects (and growing). Also, at times models need to interact (as the interaction above between user data and customer data), which can't be done in a static method without breaking encapsulation. I envision adding another layer to this (exposing web services), so knowing there are going to be 3 "controllers" at some point I need to encapsulate this CRUD somewhere (obviously), but are static methods the way to go, or is there another road? Your input is much appreciated.

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  • Where should I put contextual data related to an Object that is not really a property of the object?

    - by RenderIn
    I have a Car class. It has three properties: id, color and model. In a particular query I want to return all the cars and their properties, and I also want to return a true/false field called "searcherKnowsOwner" which is a field I calculate in my database query based on whether or not the individual conducting the search knows the owner. I have a database function that takes the ID of the searcher and the ID of the car and returns a boolean. My car class looks like this (pseudocode): class Car{ int id; Color color; Model model; } I have a screen where I want to display all the cars, but I also want to display a flag next to each car if the person viewing the page knows the owner of that car. Should I add a field to the Car class, a boolean searcherKnowsOwner? It's not a property of the car, but is actually a property of the user conducting the search. But this seems like the most efficient place to put this information.

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  • How do I write this MySQL query?

    - by CT
    I am working on an Asset DB using a lamp stack. In this example consider the following 5 tables: asset, server, laptop, desktop, software All tables have a primary key of id, which is a unique asset id. Every object has all asset attributes and then depending on type of asset has additional attributes in the corresponding table. If the type is a server, desktop or laptop it also has items in the software table. Here are the table create statements: // connect to mysql server and database "asset_db" mysql_connect("localhost", "asset_db", "asset_db") or die(mysql_error()); mysql_select_db("asset_db") or die(mysql_error()); // create asset table mysql_query("CREATE TABLE asset( id VARCHAR(50) PRIMARY KEY, company VARCHAR(50), location VARCHAR(50), purchase_date VARCHAR(50), purchase_order VARCHAR(50), value VARCHAR(50), type VARCHAR(50), notes VARCHAR(200))") or die(mysql_error()); echo "Asset Table Created.</br />"; // create software table mysql_query("CREATE TABLE software( id VARCHAR(50) PRIMARY KEY, software VARCHAR(50), license VARCHAR(50))") or die(mysql_error()); echo "Software Table Created.</br />"; // create laptop table mysql_query("CREATE TABLE laptop( id VARCHAR(50) PRIMARY KEY, manufacturer VARCHAR(50), model VARCHAR(50), serial_number VARCHAR(50), esc VARCHAR(50), user VARCHAR(50), prev_user VARCHAR(50), warranty VARCHAR(50))") or die(mysql_error()); echo "Laptop Table Created.</br />"; // create desktop table mysql_query("CREATE TABLE desktop( id VARCHAR(50) PRIMARY KEY, manufacturer VARCHAR(50), model VARCHAR(50), serial_number VARCHAR(50), esc VARCHAR(50), user VARCHAR(50), prev_user VARCHAR(50), warranty VARCHAR(50))") or die(mysql_error()); echo "Desktop Table Created.</br />"; // create server table mysql_query("CREATE TABLE server( id VARCHAR(50) PRIMARY KEY, manufacturer VARCHAR(50), model VARCHAR(50), warranty VARCHAR(50))") or die(mysql_error()); echo "Server Table Created.</br />"; ?> How do I query the database so that if I search by id, I receive all related fields to that asset id? Thank you.

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  • Game architecture: modeling different steps/types of UI

    - by Sander
    I have not done any large game development projects, only messed around with little toy projects. However, I never found an intuitive answer to a specific design question. Namely, how are different types/states of UI modeled in games? E.g. how is a menu represented? How is it different from a "game world" state (let's use an FPS as an example). How is an overlaid menu on top of a "game world" modeled? Let's imagine the main loop of a game. Where do the game states come into play? It it a simple case-by-case approach? if (menu.IsEnabled) menu.Process(elapsedTime); if (world.IsEnabled) world.Process(elapsedTime); if (menu.IsVisible) menu.Draw(); if (world.IsVisible) world.Draw(); Or are menu and world represented somewhere in a different logic layer and not represented at this level? (E.g. a menu is just another high-level entity like e.g. player input or enemy manager, equal to all others) foreach (var entity in game.HighLevelEntities) entity.Process(elapsedTime); foreach (var entity in game.HighLevelEntities) entity.Draw(elapsedTime); Are there well-known design patterns for this? Come to think of it, I don't know any game-specific design patterns - I assume there are others, as well? Please tell me about them.

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  • Where can a self-teacher learn general good programming habits and conventions?

    - by lucid
    A few mistakes and general childishness in early adulthood have left me in a situation where I work a menial job, with no possibility (in the near future) of attending school. I aspire to one day work in the programming field (gaming specifically), after proving myself on the indie end of things. I've gotten very confident in C++, java, and python, and I find I'm able to solve any problem I want either from previous experience, or from scouring the web for help. The solutions work, and with each attempt they become more readable, maintainable, and extensible. But this is because I'm learning from mistakes and bad programming and design habits I feel I might have avoided with actual schooling. General tips like: "if it's hard to read or getting long, or you're writing it twice, it should be in one or more functions." or "design all your classes before you start coding, so you don't have to rewrite classes later when you discover an unforeseen dependency" Is there a good book or website for learning general good programming practices and design habits? Also, naming and format conventions. I realize sometimes development houses have their own conventions, but things like "Classes in python usually have the first letter of each word capitalized". I'd like to be able to show some source code to a potential employer, and be prepared when for what's expected on a team. Is there some central database of naming and formatting conventions somewhere? Also, feel free to give any thoughts on whether or not the self-teach, garner some indie sales, use them as your resume' route is realistic

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  • What's the best way to store Logon User information for Web Application?

    - by Morgan Cheng
    I was once in a project of web application developed on ASP.NET. For each logon user, there is an object (let's call it UserSessionObject here) created and stored in RAM. For each HTTP request of given user, matching UserSessoinObject instance is used to visit user state information and connection to database. So, this UserSessionObject is pretty important. This design brings several problems found later: 1) Since this UserSessionObject is cached in ASP.NET memory space, we have to config load balancer to be sticky connection. That is, HTTP request in single session would always be sent to one web server behind. This limit scalability and maintainability. 2) This UserSessionObject is accessed in every HTTP request. To keep the consistency, there is a exclusive lock for the UserSessionObject. Only one HTTP request can be processed at any given time because it must to obtain the lock first. The performance and response time is affected. Now, I'm wondering whether there is better design to handle such logon user case. It seems Sharing-Nothing-Architecture helps. That means long user info is retrieved from database each time. I'm afraid that would hurt performance. Is there any design pattern for long user web app? Thanks.

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  • C++ Matrix class hierachy

    - by bpw1621
    Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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