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• Implementation details of database synchronisation API

  - by Daniel

  I want to achieve a database synchronisation between my server database and a client application. The server would run MySQL and the applications may run different database technologies, their implementation isn't important. I have a MySQL database online and web accessible via an API I wrote in PHP (just a detail). My client application ships with a copy of the online data. As time passes my goal is to check for any changes in the online database and make these updates available to the client app via an API call, by sending a date to an API endpoint corresponding to the last date the app was updated, the response would be a JSON filled with all new objects and updated objects, and delete IDs, this makes possible to update the local store appropriately. Essentially I want to do this: http://dbconvert.com/synchronization.php My question is about the implementation details. Would I need to add a column to my database tables with a "last modified" date? Since the client app could be very out of date if it's been offline for a long time, does that also mean I shouldn't delete data from the online database but instead have another column called "delete" set to 1 and a modified date updated appropriately? Would my SQL query simply check for all data with a modified date superior then the date passed into the API request by the client? I feel like there's a lot more to it then having a ton of dates everywhere. And also, worry that I will need to persist a lot of old data in order to ensure that old versions of the client app always have the opportunity to delete parts of their data when they are able to sync.

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• Combining template method with strategy

  - by Mekswoll

  An assignment in my software engineering class is to design an application which can play different forms a particular game. The game in question is Mancala, some of these games are called Wari or Kalah. These games differ in some aspects but for my question it's only important to know that the games could differ in the following: The way in which the result of a move is handled The way in which the end of the game is determined The way in which the winner is determined The first thing that came to my mind to design this was to use the strategy pattern, I have a variation in algorithms (the actual rules of the game). The design could look like this: I then thought to myself that in the game of Mancala and Wari the way the winner is determined is exactly the same and the code would be duplicated. I don't think this is by definition a violation of the 'one rule, one place' or DRY principle seeing as a change in rules for Mancala wouldn't automatically mean that rule should be changed in Wari as well. Nevertheless from the feedback I got from my professor I got the impression to find a different design. I then came up with this: Each game (Mancala, Wari, Kalah, ...) would just have attribute of the type of each rule's interface, i.e. WinnerDeterminer and if there's a Mancala 2.0 version which is the same as Mancala 1.0 except for how the winner is determined it can just use the Mancala versions. I think the implementation of these rules as a strategy pattern is certainly valid. But the real problem comes when I want to design it further. In reading about the template method pattern I immediately thought it could be applied to this problem. The actions that are done when a user makes a move are always the same, and in the same order, namely: deposit stones in holes (this is the same for all games, so would be implemented in the template method itself) determine the result of the move determine if the game has finished because of the previous move if the game has finished, determine who has won Those three last steps are all in my strategy pattern described above. I'm having a lot of trouble combining these two. One possible solution I found would be to abandon the strategy pattern and do the following: I don't really see the design difference between the strategy pattern and this? But I am certain I need to use a template method (although I was just as sure about having to use a strategy pattern). I also can't determine who would be responsible for creating the TurnTemplate object, whereas with the strategy pattern I feel I have families of objects (the three rules) which I could easily create using an abstract factory pattern. I would then have a MancalaRuleFactory, WariRuleFactory, etc. and they would create the correct instances of the rules and hand me back a RuleSet object. Let's say that I use the strategy + abstract factory pattern and I have a RuleSet object which has algorithms for the three rules in it. The only way I feel I can still use the template method pattern with this is to pass this RuleSet object to my TurnTemplate. The 'problem' that then surfaces is that I would never need my concrete implementations of the TurnTemplate, these classes would become obsolete. In my protected methods in the TurnTemplate I could just call ruleSet.determineWinner(). As a consequence, the TurnTemplate class would no longer be abstract but would have to become concrete, is it then still a template method pattern? To summarize, am I thinking in the right way or am I missing something easy? If I'm on the right track, how do I combine a strategy pattern and a template method pattern? This is part of a homework assignment but I'm not looking to be gifted the answer, I have deliberately been very verbose in my question to show that I have thought about it before coming here to ask a question

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• Ruby on Rails resources

  - by andrewpthorp

  I was hoping I could find some good ruby on rails reading/resources. Please note, I currently am aware of the following: Pragmatic Bookshelf (Exceptional Ruby, Agile web development with rails, etc) Addison Wesley (Rails AntiPatterns, The Rails 3 Way, etc) freenode #rubyonrails RSS Feeds (thoughtbot, pivotal blabs) railscasts I am looking for any other good resources. What are the best RSS feeds? What are the best books? Blogs? Videos? Any information you can share would be great!

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• Collaboration using github and testing the code

  - by wyred

  The procedure in my team is that we all commit our code to the same development branch. We have a test server that runs updated code from this branch so that we can test our code on the servers. The problem is that if we want to merge the development branch to the master branch in order to publish new features to our production servers, some features that may not have been ready will be applied to the production servers. So we're considering having each developer work on a feature/topic branch where each of them work on their own features and when it's ready, merge it into the development branch for testing, and then into the master branch. However, because our test server only pulls changes from the development branch, the developers are unable to test their features. While this is not a huge issue as they can test it on their local machine, the only problem I foresee is if we want to test callbacks from third-party services like sendgrid (where you specify a url for sendgrid to update you on the status of emails sent out). How to handle this problem? Note: We're not advanced git users. We use the Github app for MacOSX and Windows to commit our work.

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• Browser-based GUI for a python application

  - by ack__

  I want to create a web/browser-based GUI for a command-line python application. The goal is to make use of HTML/JS technologies to create this GUI. As the application itself, it needs to run on Linux and Windows, and the interface will be accessible only from localhost (not exposed to internet). The GUI will contain 5 to 10 pages. I don't want a traditional desktop GUI that includes HTML/JS, but just a bunch of html files and some kind of controller between those and the application. I also want to make use of asynchronous programming (ajax like) so I can load and print data in the GUI without refreshing the whole page. I'd probably use jQuery for that and a couple other things. How would you recommend to design this? Performance is not the key here, I'm rather looking at reliability, portability and simplicity. I'm thinking of using a lightweight python HTTP server / framework (like CherryPy) and maybe later a Python templating system (at the begining it will just be a couple pages). EDIT: I'm looking for ideas/recommendations how to build this, not for alternatives to browser/web-based GUI.

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• Low level Linux graphics

  - by math4tots

  For educational purposes, I'd like to write an application on a Linux environment that can process keyboard events and draw graphics without huge dependencies like X or SDL. I presume that this must be possible, because X and SDL are just programs themselves, so they must rely on other methods inherent to the environment. Is this understanding correct? If so, where might I learn to write such a program? My limited experience tells me that it would involve making calls to the kernel, and/or writing to special files; however, I haven't been able to find any tutorials on the matter (I am not even sure what to Google). Also, in case it is relevant, I am running Debian Squeeze on Virtualbox. I have used a netinst cd without networking, so there isn't much installed on it currently. I will install gcc, but I am hoping I can get by with nothing more.

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• How do I classify using GLCM and SVM Classifier in Matlab?

  - by Gomathi

  I'm on a project of liver tumor segmentation and classification. I used Region Growing and FCM for liver and tumor segmentation respectively. Then, I used Gray Level Co-occurence matrix for texture feature extraction. I have to use Support Vector Machine for Classification. But I don't know how to normalize the feature vectors. Can anyone tell how to program it in Matlab? To the GLCM program, I gave the tumor segmented image as input. Was I correct? If so, I think, then, my output will also be correct. My glcm coding, as far as I have tried is, I = imread('fzliver3.jpg'); GLCM = graycomatrix(I,'Offset',[2 0;0 2]); stats = graycoprops(GLCM,'all') t1= struct2array(stats) I2 = imread('fzliver4.jpg'); GLCM2 = graycomatrix(I2,'Offset',[2 0;0 2]); stats2 = graycoprops(GLCM2,'all') t2= struct2array(stats2) I3 = imread('fzliver5.jpg'); GLCM3 = graycomatrix(I3,'Offset',[2 0;0 2]); stats3 = graycoprops(GLCM3,'all') t3= struct2array(stats3) t=[t1;t2;t3] xmin = min(t); xmax = max(t); scale = xmax-xmin; tf=(x-xmin)/scale Was this a correct implementation? Also, I get an error at the last line. My output is: stats = Contrast: [0.0510 0.0503] Correlation: [0.9513 0.9519] Energy: [0.8988 0.8988] Homogeneity: [0.9930 0.9935] t1 = Columns 1 through 6 0.0510 0.0503 0.9513 0.9519 0.8988 0.8988 Columns 7 through 8 0.9930 0.9935 stats2 = Contrast: [0.0345 0.0339] Correlation: [0.8223 0.8255] Energy: [0.9616 0.9617] Homogeneity: [0.9957 0.9957] t2 = Columns 1 through 6 0.0345 0.0339 0.8223 0.8255 0.9616 0.9617 Columns 7 through 8 0.9957 0.9957 stats3 = Contrast: [0.0230 0.0246] Correlation: [0.7450 0.7270] Energy: [0.9815 0.9813] Homogeneity: [0.9971 0.9970] t3 = Columns 1 through 6 0.0230 0.0246 0.7450 0.7270 0.9815 0.9813 Columns 7 through 8 0.9971 0.9970 t = Columns 1 through 6 0.0510 0.0503 0.9513 0.9519 0.8988 0.8988 0.0345 0.0339 0.8223 0.8255 0.9616 0.9617 0.0230 0.0246 0.7450 0.7270 0.9815 0.9813 Columns 7 through 8 0.9930 0.9935 0.9957 0.9957 0.9971 0.9970 ??? Error using ==> minus Matrix dimensions must agree. The images are:

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• I need to develop a parser. Can I use Lex and Yacc for the purpose?

  - by Scrooge

  I need to extract very particular data from log files(of different types and formats). Since I am a recent college passout; my mind ran to using Lex and Yacc for the purpose. Now I have the following Questions 1. Will it be legal to do so ? (This product I am working for belongs to one of the biggest tech companies in the world.) 2. Also ; I would like to know if I am being too afraid to write my own parser? 3. How can I use Lex and Yacc if my product is Windows based? Please tell me if you need any clarification or extra information.

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• TDD - what are the short term gains/benefits?

  - by ratkok

  Quite often benefits of using TDD are considered as 'long term' gains - the overall code will be better structured, more testable, overall less bugs reported by customers, etc. However, where are the short terms benefits of using TDD? Are there any which are actually tengible and easily measureable? Is it important to have an obvious (or even not obvious by quantifiable) short term benefit at all, if the long term gains are measurable?

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• Why am I getting this error : "ExecuteReader: Connection property has not been initialized." [migrated]

  - by Olga

  I'm trying to read .csv file to import its contents to SQL table I'm getting error: ExecuteReader: Connection property has not been initialized. at the last line of this code: Function ImportData(ByVal FU As FileUpload, ByVal filename As String, ByVal tablename As String) As Boolean Try Dim xConnStr As String = "Driver={Microsoft Text Driver (*.txt; *.csv)};dbq=" & Path.GetDirectoryName(Server.MapPath(filename)) & ";extensions=asc,csv,tab,txt;" ' create your excel connection object using the connection string Dim objXConn As New System.Data.Odbc.OdbcConnection(xConnStr.Trim()) objXConn.Open() Dim objCommand As New OdbcCommand(String.Format("SELECT * FROM " & Path.GetFileName(Server.MapPath(filename)), objXConn)) If objXConn.State = ConnectionState.Closed Then objXConn.Open() Else objXConn.Close() objXConn.Open() End If ' create a DataReader Dim dr As OdbcDataReader dr = objCommand.ExecuteReader()

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• What should you leave behind for your successors?

  - by SnOrfus

  Assume that you're a sole developer leaving a job. What kind of information/material, outside of the code itself, should you create and leave behind for your replacement? An obvious answer is "whatever you would want at a new job" for sure, but it's been a while since I started a new job, and I forget what the most important things that I needed were back then. I'm thinking: accounts/passwords location of equpiment What else?

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• WPF TextBlock refresh in real time

  - by TheOnlyBrien

  I'm new to C#, in fact, this is one of the first projects I've tried to start on my own. I am curious why the TextBlock will not refresh with the following code? The WPF window does not even show up when I add the "while" loop to the code. I just want this to have a real time display of the days since I was born. Please help me out or give me constructive direction. using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows; using System.Windows.Controls; using System.Windows.Data; using System.Windows.Documents; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Imaging; using System.Windows.Navigation; using System.Windows.Shapes; namespace daysAliveWPF { /// <summary> /// Interaction logic for MainWindow.xaml /// </summary> public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); DateTime myBirthday = new DateTime(1984, 01, 19); while (true) { TimeSpan daysAlive = DateTime.Now.Subtract(myBirthday); MyTextBlock.Text = daysAlive.TotalDays.ToString(); } } } } Similar code has worked in a Console Window application, so I don't understand what's going on here. Console Application code snip that did work is: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace DisplayRealTime { class Program { static void Main(string[] args) { DateTime myBirthday = new DateTime(1984, 06, 19); while (true) { TimeSpan daysAlive = DateTime.Now.Subtract(myBirthday); Console.Write("\rTotal Days Alive: {0}", daysAlive.TotalDays.ToString(".#####")); } } } } Thank you!

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• Can python and php work together?

  - by user71741

  I am having a mobile app created for ios. The developers built the app in php. The app requires an algorithm so I found another programmer to develop it. The algorithm programmer built the algorithm in python. The developers refuse to finish the app because they say it won't work with python, while the programmer insist it will. The programmer says put the algorithm in its on server and connect then over http. Will this work and I'd so how risky is it to future problems?

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• A design pattern for data binding an object (with subclasses) to asp.net user control

  - by Rohith Nair

  I have an abstract class called Address and I am deriving three classes ; HomeAddress, Work Address, NextOfKin address. My idea is to bind this to a usercontrol and based on the type of Address it should bind properly to the ASP.NET user control. My idea is the user control doesn't know which address it is going to present and based on the type it will parse accordingly. How can I design such a setup, based on the fact that, the user control can take any type of address and bind accordingly. I know of one method like :- Declare class objects for all the three types (Home,Work,NextOfKin). Declare an enum to hold these types and based on the type of this enum passed to user control, instantiate the appropriate object based on setter injection. As a part of my generic design, I just created a class structure like this :- I know I am missing a lot of pieces in design. Can anybody give me an idea of how to approach this in proper way.

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• Integrating different branches from external sources into a single Mercurial repository

  - by dukeofgaming

  I'm currently working in a company using Perforce and am making way for distributed version control with Mercurial. I've had success importing Perforce history using the perfarce (quite a suitable name, I laugh every time I see/say it) however, this only works with a single branch at a time. Here's how my P4 integration setup works: In perforce, create a "client", which is kind of a description of what you will be constantly updating/checking-out. This can only address one branch at a time (trunk or other). Once you do this, run hg clone p4://<server>/<client_name> Go to .hg/hgrc and put the perforce path line: perforce = p4://<server>/<client_name> Work normally with the code under mercurial, do hg pull perforce to sync up, hg push to export a changelist What I'd like to be able to do is have a perforce path per branch and have everything work in the same repository. Now, pushing is not a problem, however, if I pull the history from another branch it would end up at the default branch. I'd like to be able to do something like hg pull perforce-R5 and have it land in mercurial's R5 branch. Even if I have no merging history, it would be sweet enough to be able to preserve it. There are also other plugins for CVCSs that let you integrate mercurial, but AFAIK the subversion one has the same problem. I don't think there is a straight-through way of doing this, but as long as I could automate the process with some hooks and scripts in a single Mercurial machine, that would be good enough.

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• How much should I charge an hour for freelance iOS development?

  - by Tyler Bell

  I am a fairly competent developer who already holds a job developing iOS applications. This job is through the university which I attend. The producer of the apps that I develop is always trying to set me up with some freelance opportunities to get my work out there and to get me some more work/experience. What is a reasonable price to charge (either hourly or per app)? I'd be working by myself, on my own equipment, from start to finish in the design process. Just wondering what a reasonable price was...I've heard up to $30? Thanks

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• Why and when should I make a class 'static'? What is the purpose of 'static' keyword on classes?

  - by Saeed Neamati

  The static keyword on a member in many languages mean that you shouldn't create an instance of that class to be able to have access to that member. However, I don't see any justification to make an entire class static. Why and when should I make a class static? What benefits do I get from making a class static? I mean, after declaring a static class, one should still declare all members which he/she wants to have access to without instantiation, as static too. This means that for example, Math class could be declared normal (not static), without affecting how developers code. In other words, making a class static or normal is kind of transparent to developers.

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• How do you get better at selling your idea/software/pitch?

  - by Sergio Tapia

  How do I gain the skills to properly pitch my ideas/bids to potential clients? What are the tried and true methods of improving this very necessary skill a freelancer is supposed to have in order to survive? I have a bit of trouble trying to sell my ideas to clients and convince them that this project can be done and done well within the time they ask, but so far I feel I'm lacking in that department and I want to WOW the pants off clients from here on out. Any suggestions?

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• What is the greatest design flaw you have faced in any programming language?

  - by Anto

  All programming languages are having their design flaws simply because not a single language can be perfect, just as with most (all?) other things. That aside, which design fault in a programming language has annoyed you the most through your history as a programmer? Note that if a language is "bad" just because it isn't designed for a specific thing isn't a design flaw, but a feature of design, so don't list such annoyances of languages. If a language is illsuited for what it is designed for, that is of course a flaw in the design. Implementation specific things and under the hood things do not count either.

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• Why is design by contract considered an alternative to the pseudo programming process?

  - by zoopp

  Right now I'm reading Code Complete by Steve McConnell and in chapter 9 he talks about the Pseudo Programming Process (PPP). From what I've understood, the PPP is a way of programming in which the programmer first writes the pseudo code for the routine he's working on, then refines it up to the point where pretty much each pseudo code line can be implemented in 1-3 lines of code, then writes the code in the designated programming language and finally the pseudo code is saved as comments for the purpose of documenting the routine. In chapter 9.4 the author mentions alternatives to the PPP, one of which is 'design by contract'. In design by contract you basically assert preconditions and postconditions of each routine. Now why would that be considered an alternative? To me it seems obvious that I should use both techniques at the same time and not chose one over the other.

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• What about introduction to programming with C# via LINQPad?

  - by Gulshan

  From different questions/answers/articles in this and some other sites, I got the idea that the introductory language for programming should be- High level Less verbose C# is one of the heavily used high level languages being used these days. It's also multi-paradigm and descendant of C, the lingua-franca of all programming languages. So, I think it has the potential to be the introductory programming language. But I felt it's a bit verbose for the novice learners. Then LINQPad came into my mind. With LINQPad, someone can start with C# without it's verbosity. Because you can just run one statement or few statements or a standalone function with LINQPad. Again you can run a full source file also. Another thing it provide is- using SQL. So, it can be used for learning SQL too. And not to mention, it's free. So, what you guys think about the idea of introducing programming with C# via LINQPad? Any thing to watch out? Any suggestion?

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• java development of products and automation development

  - by momo

  I'm a java developer working on j2ee development, on real products (not inhouse tools). I found another job to work on development of test automation frameworks / continuous integration. is development of test automation frameworks will affect my skill set ?is it considered to be less reputed and less needed? (the reason im confused is that the new role salary is higher).. do you think I should give up this offer and continue seeking a development role within the domain technolgies (java / j2ee) ?

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• Is there a Javascript library for creating vintage photos?

  - by Nguyen Thanh Tu

  I'm working on a Canvas object in HTML5, and I am attempting to make some photos look "better". I tried VintageJS, an existing photo-retouching Javascript library, and Picozu, a web application cloning some Adobe Photoshop functionalities, but I'm still not happy. Can you help me with an algorithm or point to an existing Javascript library that would allow me to make my photos look like the following example? http://i46.photobucket.com/albums/f137/thanhtu_zx/Untitled-1.jpg

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• Thoughts on web development architecture through integrating C++ in the future to a web application

  - by Holland

  I'm looking to build a website (it's actually going to be a commercial startup) I saw this question and it really shed some light on a few things that I was hoping to understand (kudos to the op). After seeing that, it would make sense that, unless the website were required to actually have millions of hits per day, it wouldn't be a viable solution to write a C++ backend on the server side. But this got me thinking. what if it in the (unlikely) events of the future, it does go that route? The problem is that, while I'm thinking of starting this all using .Net (in the beginning) just to get something quick and easy up without a lot of hassle (in terms of learning), and then moving towards something more Open Source (such as Python/Django or RoR) later to save money and to support OSS, I'm wondering IFF the website actually becomes big, will it be a good idea to integrate a C++ backend, and use Python ontop of C++ for a strong foundation, and then mitigate HTML/CSS/AJAX/etc ontop of the backend's foundation? I guess, what I'd like to know is that, given the circumstance, if this were to happen, would it be a proper approach in terms of architecture? I'd definitely be supporting MVC as that seems to be a great way to implement a website. All in all, would one consider this rational, or are there other alternatives? I like .Net, and I'd like to use it in the beginning, because I have much more experience with that than, say, Python or PHP, and I prefer it in general, but I really do want to support OSS in the future. I suppose the sentence I'm looking for is, "is this pragmatic?"

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• What can Haskell's type system do that Java's can't?

  - by Matt Fenwick

  I was talking to a friend about the differences between the type systems of Haskell and Java. He asked me what Haskell's could do that Java's couldn't, and I realized that I didn't know. After thinking for a while, I came up with a very short list of minor differences. Not being heavy into type theory, I'm left wondering whether they're formally equivalent. To try and keep this from becoming a subjective question, I'm asking: what are the major, non-syntactical differences between their type systems? I realize some things are easier/harder in one than in the other, and I'm not interested in talking about those. And to make it more specific, let's ignore Haskell type extensions since there's so many out there that do all kinds of crazy/cool stuff.

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