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• Application/Server dependency mapping

  - by David Stratton

  I'm just curious as to whether such as tool exists (free, open source, or commercial but for a reasonable price) before I build it myself. We're looking for a simple solution to simplify taking web apps online and offline when a server is undergoing maintenance. The idea is that we be able to mark a server as unavailable, and then mark all dependent (direct and indirect) as offline. Our first proof-of-concept is running, and we created an aspx page that lists various applications that have an App_Offline.html file with a friendly "Down for Maintenance" message in a GridView. In the GridView, each app has a LinkButton that, when clicked, either renames the App_Offline.htm to App_Offline.html or vice-versa to take the app online and offline. The next step is to set up all of our dependencies. For example, our store locater would be dependent on our web services, which in turn are dependent on our SQL Server. (that's a simple example. We can easily have several layers, or one app dependent on multiple servers, etc.) In this example, if the SQL server goes down, we would need to drill down recursively to find all apps that depend on it, and then turn them off and on by renaming the App_Offline file appropriately. I realize this will be relatively simple to build, but could be complex to manage. I'm sure we're not the first team to think of this concept, and I'm wondering if there are any open source tools, or if any of you have done something similar and can help us avoid pitfalls. Edit - Update I found the category of software I'm looking for. it's called CMDB - (Configuration Management Database), and it's generally more of a Network Admin type tool than a developer tool. I found some open source products in this category, but none written in .NET. I had considered moving this question to ServerFault.com when I realized I was looking for a netowrk Admin type tool, but since I'm looking for code and a modifiable solution I'll keep the question here.

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• HTML 4, HTML 5, XHTML, MIME types - the definitive resource

  - by deceze

  The topics of HTML vs. XHTML and XHTML as text/html vs. XHTML as XHTML are quite complex. Unfortunately it's hard to get a complete picture, since information is spread mostly in bits and pieces around the web or is buried deep in W3C tech jargon. In addition there's some misinformation being circulated. I propose to make this the definite SO resource about the topic, describing the most important aspects of: HTML 4 HTML 5 XHTML 1.0/1.1 as text/html XHTML 1.0/1.1 as XHTML What are the practical implications of each? What are common pitfalls? What is the importance of proper MIME types for each? How do different browsers handle them? I'd like to see one answer per technology. I'm making this a community wiki, so rather than contributing redundant answers, please edit answers to complete the picture. Feel free to start with stubs. Also feel free to edit this question.

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• What is the worst programming language you ever worked with? [closed]

  - by Ludwig Weinzierl

  If you have an interesting story to share, please post an answer, but do not abuse this question for bashing a language. We are programmers, and our primary tool is the programming language we use. While there is a lot of discussion about the best one, I'd like to hear your stories about the worst programming languages you ever worked with and I'd like to know exactly what annoyed you. I'd like to collect this stories partly to avoid common pitfalls while designing a language (especially a DSL) and partly to avoid quirky languages in the future in general. This question is not subjective. If a language supports only single character identifiers (see my own answer) this is bad in a non-debatable way. EDIT Some people have raised concerns that this question attracts trolls. Wading through all your answers made one thing clear. The large majority of answers is appropriate, useful and well written. UPDATE 2009-07-01 19:15 GMT The language overview is now complete, covering 103 different languages from 102 answers. I decided to be lax about what counts as a programming language and included anything reasonable. Thank you David for your comments on this. Here are all programming languages covered so far (alphabetical order, linked with answer, new entries in bold): ABAP, all 20th century languages, all drag and drop languages, all proprietary languages, APF, APL (1), AS400, Authorware, Autohotkey, BancaStar, BASIC, Bourne Shell, Brainfuck, C++, Centura Team Developer, Cobol (1), Cold Fusion, Coldfusion, CRM114, Crystal Syntax, CSS, Dataflex 2.3, DB/c DX, dbase II, DCL, Delphi IDE, Doors DXL, DOS batch (1), Excel Macro language, FileMaker, FOCUS, Forth, FORTRAN, FORTRAN 77, HTML, Illustra web blade, Informix 4th Generation Language, Informix Universal Server web blade, INTERCAL, Java, JavaScript (1), JCL (1), karol, LabTalk, Labview, Lingo, LISP, Logo, LOLCODE, LotusScript, m4, Magic II, Makefiles, MapBasic, MaxScript, Meditech Magic, MEL, mIRC Script, MS Access, MUMPS, Oberon, object extensions to C, Objective-C, OPS5, Oz, Perl (1), PHP, PL/SQL, PowerDynamo, PROGRESS 4GL, prova, PS-FOCUS, Python, Regular Expressions, RPG, RPG II, Scheme, ScriptMaker, sendmail.conf, Smalltalk, Smalltalk , SNOBOL, SpeedScript, Sybase PowerBuilder, Symbian C++, System RPL, TCL, TECO, The Visual Software Environment, Tiny praat, TransCAD, troff, uBasic, VB6 (1), VBScript (1), VDF4, Vimscript, Visual Basic (1), Visual C++, Visual Foxpro, VSE, Webspeed, XSLT The answers covering 80386 assembler, VB6 and VBScript have been removed.

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• HTML 4, HTML 5, XHTML, MIME types - the definite resource

  - by deceze

  The topics of HTML vs. XHTML and XHTML as text/html vs. XHTML as XHTML are quite complex. Unfortunately it's hard to get a complete picture, since information is spread mostly in bits and pieces around the web or is buried deep in W3C tech jargon. In addition there's some misinformation being circulated. I propose to make this the definite SO resource about the topic, describing the most important aspects of: HTML 4 HTML 5 XHTML 1.0/1.1 as text/html XHTML 1.0/1.1 as XHTML What are the practical implications of each? What are common pitfalls? What is the importance of proper MIME types for each? How do different browsers handle them? I'd like to see one answer per technology. I'm making this a community wiki, so rather than contributing redundant answers, please edit answers to complete the picture. Feel free to start with stubs. Also feel free to edit this question.

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• Evaluation of environment variables in command run by Java's Runtime.exec()

  - by Tom Duckering

  Hi, I have a scenarios where I have a Java "agent" that runs on a couple of platforms (specifically Windows, Solaris & AIX). I'd like to factor out the differences in filesystem structure by using environment variables in the command line I execute. As far as I can tell there is no way to get the Runtime.exec() method to resolve/evaluate any environment variables referenced in the command String (or array of Strings). I know that if push comes to shove I can write some code to pre-process the command String(s) and resolve enviroment variables by hand (using getEnv() etc). However I'm wondering if there is a smarter way to do this since I'm sure I'm not the only person wanting to do this and I'm sure there are pitfalls in "knocking up" my own implementation. Your guidance and suggestions are most welcome. edit: I would like to refer to environment variables in the command string using some consistent notation such as $VAR and/or %VAR%. Not fussed which. edit: To be clear I'd like to be able to execute a command such as: perl $SCRIPT_ROOT/somePerlScript.pl args on Windows and Unix hosts using Runtime.exec(). I specify the command in config file that describes a list of jobs to run and it has to be able to work cross platform, hence my thought that an environment variable would be useful to factor out the filesystem differences (/home/username/scripts vs C:\foo\scripts). Hope that helps clarify it. Thanks. Tom

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• Simulating Google Appengine's Task Queue with Gearman

  - by sotangochips

  One of the characteristics I love most about Google's Task Queue is its simplicity. More specifically, I love that it takes a URL and some parameters and then posts to that URL when the task queue is ready to execute the task. This structure means that the tasks are always executing the most current version of the code. Conversely, my gearman workers all run code within my django project -- so when I push a new version live, I have to kill off the old worker and run a new one so that it uses the current version of the code. My goal is to have the task queue be independent from the code base so that I can push a new live version without restarting any workers. So, I got to thinking: why not make tasks executable by url just like the google app engine task queue? The process would work like this: User request comes in and triggers a few tasks that shouldn't be blocking. Each task has a unique URL, so I enqueue a gearman task to POST to the specified URL. The gearman server finds a worker, passes the url and post data to a worker The worker simply posts to the url with the data, thus executing the task. Assume the following: Each request from a gearman worker is signed somehow so that we know it's coming from a gearman server and not a malicious request. Tasks are limited to run in less than 10 seconds (There would be no long tasks that could timeout) What are the potential pitfalls of such an approach? Here's one that worries me: The server can potentially get hammered with many requests all at once that are triggered by a previous request. So one user request might entail 10 concurrent http requests. I suppose I could have a single worker with a sleep before every request to rate-limit. Any thoughts?

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• Best Practices for Setup and Management of an Open Source Project

  - by VirtuosiMedia

  Later this year I want to release a PHP framework that I've been working on as open source. I do use source control (SVN), but it's on an extremely limited basis. I'm self-taught, I develop by myself and don't have the experience of working with large teams. I have some ideas about what can help make a project successful, but I'm fuzzy on some of the details. Since it's not yet released, I want to do everything I can to set up the right infrastructure from the beginning. What do I need to know in order to setup and manage a successful project? Some ideas that I have to make it successful (beyond marketing it): Good documentation and tutorials Automated unit tests and builds to push update to the website A clear roadmap Bug Tracking integrated with the source control A style guide to keep the code consistent along with clear A forum for the community to get support, share ideas, etc. A good example application built with the framework A blog to keep the community informed Maintaining backwards compatibility wherever possible Some of my questions: How do I setup and automate a one step submit-test-commit-generate API docs-push update to website process? How do I handle (technically) submissions from other users? How can I ensure that those submissions must be approved before being integrated? What are some of the pitfalls that can be avoided in terms of the project community? I'd prefer to have it be as friendly and helpful as possible without a lot of drama. I'd love to learn from your experience on any of these points. If you think I'm missing anything big, please share that as well. Any resources (preferably geared toward a beginner) that you could point me towards would also be greatly appreciated.

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• Accessing Item Fields via Sitecore Web Service

  - by Catch

  I am creating items on the fly via Sitecore Web Service. So far I can create the items from this function: AddFromTemplate And I also tried this link: http://blog.hansmelis.be/2012/05/29/sitecore-web-service-pitfalls/ But I am finding it hard to access the fields. So far here is my code: public void CreateItemInSitecore(string getDayGuid, Oracle.DataAccess.Client.OracleDataReader reader) { if (getDayGuid != null) { var sitecoreService = new EverBankCMS.VisualSitecoreService(); var addItem = sitecoreService.AddFromTemplate(getDayGuid, templateIdRTT, "Testing", database, myCred); var getChildren = sitecoreService.GetChildren(getDayGuid, database, myCred); for (int i = 0; i < getChildren.ChildNodes.Count; i++) { if (getChildren.ChildNodes[i].InnerText.ToString() == "Testing") { var getItem = sitecoreService.GetItemFields(getChildren.ChildNodes[i].Attributes[0].Value, "en", "1", true, database, myCred); string p = getChildren.ChildNodes[i].Attributes[0].Value; } } } } So as you can see I am creating an Item and I want to access the Fields for that item. I thought that GetItemFields will give me some value, but finding it hard to get it. Any clue?

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• Help! I've learned jQuery... now I want to learn JavaScript

  - by Derek Adair

  I am a self-taught web developer/programmer. I started out about two years ago by learning how to make simple dynamic websites with HTML/CSS/PHP. Then I started dabbling with animation... Enter jQuery I've become quite proficient with jQuery over the last year and I've even started making my own plugins. I've spent most of my effort learning how to beautify websites with fancy effects and what not. Upon tackling my first full-blown application, I realized how under-developed my knowledge of JavaScript actually is. jQuery has allowed me to rely on its framework so heavily that I rarely use any interesting functions, techniques, or whatever that are 'native' to the JavaScript language. For example: I have a basic understanding of what a closure is... but I am unsure where this technique can actually benefit me. Although as I understand it, that's what my jQuery plugins do with (function ($){//plugin code here})(jQuery). I've seen many posts/blogs/whatever about memory leaks and circular references which is concerning. I'm frustrated because I can wrap my head around the basic concepts of what these are just by reading the articles, but I'm finding that the deeper I go the more I don't understand. The vocabulary alone is burdensome. Let alone how to actually use these techniques/functions/language features. I am trying to figure out what I don't know I'm looking to gather any advice, techniques, articles, books, videos, snippets, examples, potential pitfalls... really anything you have regarding application development with JavaScript/jQuery.

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• How to speed up marching cubes?

  - by Dan Vinton

  I'm using this marching cube algorithm to draw 3D isosurfaces (ported into C#, outputting MeshGeomtry3Ds, but otherwise the same). The resulting surfaces look great, but are taking a long time to calculate. Are there any ways to speed up marching cubes? The most obvious one is to simply reduce the spatial sampling rate, but this reduces the quality of the resulting mesh. I'd like to avoid this. I'm considering a two-pass system, where the first pass samples space much more coarsely, eliminating volumes where the field strength is well below my isolevel. Is this wise? What are the pitfalls? Edit: the code has been profiled, and the bulk of CPU time is split between the marching cubes routine itself and the field strength calculation for each grid cell corner. The field calculations are beyond my control, so speeding up the cubes routine is my only option... I'm still drawn to the idea of trying to eliminate dead space, since this would reduce the number of calls to both systems considerably.

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• Java - Save video stream from Socket to File

  - by Alex

  I use my Android application for streaming video from phone camera to my PC Server and need to save them into file on HDD. So, file created and stream successfully saved, but the resulting file can not play with any video player (GOM, KMP, Windows Media Player, VLC etc.) - no picture, no sound, only playback errors. I tested my Android application into phone and may say that in this instance captured video successfully stored on phone SD card and after transfer it to PC played witout errors, so, my code is correct. In the end, I realized that the problem in the video container: data streamed from phone in MP4 format and stored in *.mp4 files on PC, and in this case, file may be incorrect for playback with video players. Can anyone suggest how to correctly save streaming video to a file? There is my code that process and store stream data (without errors handling to simplify): // getOutputMediaFile() returns a new File object DataInputStream in = new DataInputStream (server.getInputStream()); FileOutputStream videoFile = new FileOutputStream(getOutputMediaFile()); int len; byte buffer[] = new byte[8192]; while((len = in.read(buffer)) != -1) { videoFile.write(buffer, 0, len); } videoFile.close(); server.close(); Also, I would appreciate if someone will talk about the possible "pitfalls" in dealing with the conservation of media streams. Thank you, I hope for your help! Alex.

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• IUsable: controlling resources in a better way than IDisposable

  - by Ilya Ryzhenkov

  I wish we have "Usable" pattern in C#, when code block of using construct would be passed to a function as delegate: class Usable : IUsable { public void Use(Action action) // implements IUsable { // acquire resources action(); // release resources } } and in user code: using (new Usable()) { // this code block is converted to delegate and passed to Use method above } Pros: Controlled execution, exceptions The fact of using "Usable" is visible in call stack Cons: Cost of delegate Do you think it is feasible and useful, and if it doesn't have any problems from the language point of view? Are there any pitfalls you can see? EDIT: David Schmitt proposed the following using(new Usable(delegate() { // actions here }) {} It can work in the sample scenario like that, but usually you have resource already allocated and want it to look like this: using (Repository.GlobalResource) { // actions here } Where GlobalResource (yes, I know global resources are bad) implements IUsable. You can rewrite is as short as Repository.GlobalResource.Use(() => { // actions here }); But it looks a little bit weird (and more weird if you implement interface explicitly), and this is so often case in various flavours, that I thought it deserve to be new syntactic sugar in a language.

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• Are there some cases where Python threads can safely manipulate shared state?

  - by erikg

  Some discussion in another question has encouraged me to to better understand cases where locking is required in multithreaded Python programs. Per this article on threading in Python, I have several solid, testable examples of pitfalls that can occur when multiple threads access shared state. The example race condition provided on this page involves races between threads reading and manipulating a shared variable stored in a dictionary. I think the case for a race here is very obvious, and fortunately is eminently testable. However, I have been unable to evoke a race condition with atomic operations such as list appends or variable increments. This test exhaustively attempts to demonstrate such a race: from threading import Thread, Lock import operator def contains_all_ints(l, n): l.sort() for i in xrange(0, n): if l[i] != i: return False return True def test(ntests): results = [] threads = [] def lockless_append(i): results.append(i) for i in xrange(0, ntests): threads.append(Thread(target=lockless_append, args=(i,))) threads[i].start() for i in xrange(0, ntests): threads[i].join() if len(results) != ntests or not contains_all_ints(results, ntests): return False else: return True for i in range(0,100): if test(100000): print "OK", i else: print "appending to a list without locks *is* unsafe" exit() I have run the test above without failure (100x 100k multithreaded appends). Can anyone get it to fail? Is there another class of object which can be made to misbehave via atomic, incremental, modification by threads? Do these implicitly 'atomic' semantics apply to other operations in Python? Is this directly related to the GIL?

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• Extand legacy site with another server-side programming platform best practice

  - by Andrew Florko

  Company I work for have a site developed 6-8 years ago by a team that was enthusiastic enough to use their own private PHP-based CMS. I have to put dynamic data from one intranet company database on this site in one week: 2-3 pages. I contacted company site administrator and she showed me administrative part - CMS allows only to insert html blocks & manage site map (site is deployed on machine that is inside company & fully accessible & upgradable). I'm not a PHP-guy & I don't want to dive into legacy hardly-who-ever-heard-about CMS engine I also don't want to contact developers team, 'cos I'm not sure they are still present and capable enough to extend this old days site and it'll take too much time anyway. I am about to deploy helper asp.net site on iis with 2-3 pages required & refer helper site via iframe from present site. New pages will allow to download some dynamic content from present site also. Is it ok and what are the pitfalls with iframe approach?

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• Is it bad practice to make a setter return "this"?

  - by Ken Liu

  Is it a good or bad idea to make setters in java return "this"? public Employee setName(String name){ this.name = name; return this; } This pattern can be useful because then you can chain setters like this: list.add(new Employee().setName("Jack Sparrow").setId(1).setFoo("bacon!")); instead of this: Employee e = new Employee(); e.setName("Jack Sparrow"); ...and so on... list.add(e); ...but it sort of goes against standard convention. I suppose it might be worthwhile just because it can make that setter do something else useful. I've seen this pattern used some places (e.g. JMock, JPA), but it seems uncommon, and only generally used for very well defined APIs where this pattern is used everywhere. Update: What I've described is obviously valid, but what I am really looking for is some thoughts on whether this is generally acceptable, and if there are any pitfalls or related best practices. I know about the Builder pattern but it is a little more involved then what I am describing - as Josh Bloch describes it there is an associated static Builder class for object creation.

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• Text message intent - catch and send

  - by Espen

  Hi! I want to be able to control incoming text messages. My application is still on a "proof of concept" version and I'm trying to learn Android programming as I go. First my application need to catch incomming text messages. And if the message is from a known number then deal with it. If not, then send the message as nothing has happened to the default text message application. I have no doubt it can be done, but I still have some concern and I see some pitfalls at how things are done on Android. So getting the incomming text message could be fairly easy - except when there are other messaging applications installed and maybe the user wants to have normal text messages to pop up on one of them - and it will, after my application has had a look at it first. How to be sure my application get first pick of incomming text messages? And after that I need to send most text messages through to any other text message application the user has chosen so the user can actually read the message my application didn't need. Since Android uses intents that are relative at best, I don't see how I can enforce my application to get a peek at all incomming text messages, and then stop it or send it through to the default text messaging application...

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• Technical choices in unmarshaling hash-consed data

  - by Pascal Cuoq

  There seems to be quite a bit of folklore knowledge floating about in restricted circles about the pitfalls of hash-consing combined with marshaling-unmarshaling of data. I am looking for citable references to these tidbits. For instance, someone once pointed me to library aterm and mentioned that the authors had clearly thought about this and that the representation on disk was bottom-up (children of a node come before the node itself in the data stream). This is indeed the right way to do things when you need to re-share each node (with a possible identical node already in memory). This re-sharing pass needs to be done bottom-up, so the unmarshaling itself might as well be, too, so that it's possible to do everything in a single pass. I am in the process of describing difficulties encountered in our own context, and the solutions we found. I would appreciate any citable reference to the kind of aforementioned folklore knowledge. Some people obviously have encountered the problems before (the aterm library is only one example). But I didn't find anything in writing. Even the little piece of information I have about aterm is hear-say. I am not worried it's not reliable (you can't make this up), but "personal communication" and "look how it's done in the source code" are considered poor form in citations. I have enough references on hash-consing alone. I am only interested in references where it interferes with other aspects of programming, such as marshaling or distribution.

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• Querying a database using Cocoa.

  - by S1syphus

  Hello everybody. Before I start a disclaimer, I should add a little disclaimer, that I am relatively new to Cocoa development and C in general. However I do have a copy of 'Cocoa Programming for Mac OS X 3rd edition' by Aaron Hillegass, which I am working through and using as a base, if anybody has a copy I am using the 'AmaZone' example on page 346 as a template and base. I trying to develop a small client app that takes a search string then displays results from a database accordingly. The database will contain a: list of files, their location, description & creation date, so for the moment the field number and types will remain the same. After looking around on SO, I saw something like: NSURL *myURL = [NSURL URLWithString:@"http://www.myserver.com/results.php"]; NSArray *sqlResults = [[NSArray alloc] initWithContentsOfURL:myURL]; I've worked with php before, so my current thinking after seeing this is create a php script on the server that queries the database, and creates an XML output. And with the XML response, just parse it. Would this be ok? as is there any major pitfalls anybody can see, that I can't. I know there are some database bundles, I've had a look at BaseTen for Postgres, but being relatively new to this, didn't want to get in over my head. Or if anybody else has any other suggestions and ideas, they would be greatly appreciated.

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• Does a CS PhD Help for Software Engineering Career?

  - by SiLent SoNG

  I would like to seek advice on whether or not to take a PhD offer from a good university. My only concern is the PhD will take at least 4 year's commitment. During the period I won't have good monetary income. I am also concerned whether the PhD will help my future career development. My career goal is software engineering only. Some of the PhD info: The PhD is CS related. The research area is Information Retrieval, Machine Learning, and Nature Language Processing. More specifically, the research topic is Deep Web search. Some of backgrounds: I worked in Oracle for 3 years in database development after obtained a CS degree from some good university. In last year I received an email telling an interesting project from a professor and thereafter I was lured into his research team. The team consists of 4 PhD students; those students have little or no industry experiences and their coding skills are really really bad. By saying bad I mean they do not know some common patterns and they do not know pitfalls of the programming languages as well as idioms for doing things right. I guess a at least 4 year commitment is worth of serious consideration. I am 27 at this moment. If I take the offer, that implies I will be 31+ upon graduation. Wah... becoming.. what to say, no longer young. Hence, here I am seeking advice on whether it is good or not to take the PhD offer, and whether a CS PhD is good for my future career growth as a software engineer? I do not intent to go for academia.

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• wrapping user controls in a transaction

  - by Hans Gruber

  I'm working on heavily dynamic and configurable CMS system. Therefore, many pages are composed of a dynamically loaded set of user controls. To enable loose coupling between containers (pages) and children (user controls), all user controls are responsible for their own persistence. Each User Control is wired up to its data/service layer dependencies via IoC. They also implement an IPersistable interface, which allows the container .aspx page to issue a Save command to its children without knowledge of the number or exact nature of these user controls. Note: what follows is only pseudo-code: public class MyUserControl : IPersistable, IValidatable { public void Save() { throw new NotImplementedException(); } public bool IsValid() { throw new NotImplementedException(); } } public partial class MyPage { public void btnSave_Click(object sender, EventArgs e) { foreach (IValidatable control in Controls) { if (!control.IsValid) { throw new Exception("error"); } } foreach (IPersistable control in Controls) { if (!control.Save) { throw new Exception("error"); } } } } I'm thinking of using declarative transactions from the System.EnterpriseService namespace to wrap the btnSave_Click in a transaction in case of an exception, but I'm not sure how this might be achieved or any pitfalls to such an approach.

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• wrapping aspx user controls commands in a transaction

  - by Hans Gruber

  I'm working on heavily dynamic and configurable CMS system. Therefore, many pages are composed of a dynamically loaded set of user controls. To enable loose coupling between containers (pages) and children (user controls), all user controls are responsible for their own persistence. Each User Control is wired up to its data/service layer dependencies via IoC. They also implement an IPersistable interface, which allows the container .aspx page to issue a Save command to its children without knowledge of the number or exact nature of these user controls. Note: what follows is only pseudo-code: public class MyUserControl : IPersistable, IValidatable { public void Save() { throw new NotImplementedException(); } public bool IsValid() { throw new NotImplementedException(); } } public partial class MyPage { public void btnSave_Click(object sender, EventArgs e) { foreach (IValidatable control in Controls) { if (!control.IsValid) { throw new Exception("error"); } } foreach (IPersistable control in Controls) { if (!control.Save) { throw new Exception("error"); } } } } I'm thinking of using declarative transactions from the System.EnterpriseService namespace to wrap the btnSave_Click in a transaction in case of an exception, but I'm not sure how this might be achieved or any pitfalls to such an approach.

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• Atomically maintaining a counter using Sub-sonic ActiveRecord

  - by cantabilesoftware

  I'm trying to figure out the correct way to atomically increment a counter in one table and use that incremented value as an pseudo display-only ID for a record in another. What I have is a companies table and a jobs table. I want each company to have it's own set of job_numbers. I do have an auto increment job_id, but those numbers are shared across all companies. ie: the job numbers should generally increment without gaps for each company. ie: companies(company_id, next_job_number) jobs(company_id, job_id, job_number) Currently I'm doing this (as a method on the partial job class): public void SaveJob() { using (var scope = new System.Transactions.TransactionScope()) { if (job_id == 0) { _db.Update<company>() .SetExpression("next_job_number").EqualTo("next_job_number+1") .Where<company>(x => x.company_id == company_id) .Execute(); company c = _db.companies.SingleOrDefault(x => x.company_id == company_id); job_number = c.next_job_number; } // Save the job this.Save(); scope.Complete(); } } It seems to work, but I'm not sure if there are pitfalls here? It just feels wrong, but I'm not sure how else to do it. Any advice appreciated.

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• Deal with undefined values in code or in the template?

  - by David

  I'm writing a web application (in Python, not that it matters). One of the features is that people can leave comments on things. I have a class for comments, basically like so: class Comment: user = ... # other stuff where user is an instance of another class, class User: name = ... # other stuff And of course in my template, I have <div>${comment.user.name}</div> Problem: Let's say I allow people to post comments anonymously. In that case comment.user is None (undefined), and of course accessing comment.user.name is going to raise an error. What's the best way to deal with that? I see three possibilities: Use a conditional in the template to test for that case and display something different. This is the most versatile solution, since I can change the way anonymous comments are displayed to, say, "Posted anonymously" (instead of "Posted by ..."), but I've often been told that templates should be mindless display machines and not include logic like that. Also, other people might wind up writing alternate templates for the same application, and I feel like I should be making things as easy as possible for the template writer. Implement an accessor method for the user property of a Comment that returns a dummy user object when the real user is undefined. This dummy object would have user.name = 'Anonymous' or something like that and so the template could access it and print its name with no error. Put an actual record in my database corresponding to a user with user.name = Anonymous (or something like that), and just assign that user to any comment posted when nobody's logged in. I know I've seen some real-world systems that operate this way. (phpBB?) Is there a prevailing wisdom among people who write these sorts of systems about which of these (or some other solution) is the best? Any pitfalls I should watch out for if I go one way vs. another? Whoever gives the best explanation gets the checkmark.

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• Java abstract visitor - guarantueed to succeed? If so, why?

  - by disown

  I was dealing with hibernate, trying to figure out the run-time class behind proxied instances by using the visitor pattern. I then came up with an AbstractVisitable approach, but I wonder if it will always produce correct results. Consider the following code: interface Visitable { public void accept(Visitor v); } interface Visitor { public void visit(Visitable visitorHost); } abstract class AbstractVisitable implements Visitable { @Override public void accept(Visitor v) { v.visit(this); } } class ConcreteVisitable extends AbstractVisitable { public static void main(String[] args) { final Visitable visitable = new ConcreteVisitable(); final Visitable proxyVisitable = (Visitable) Proxy.newProxyInstance( Thread.currentThread().getContextClassLoader(), new Class<?>[] { Visitable.class }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(visitable, args); } }); proxyVisitable.accept(new Visitor() { @Override public void visit(Visitable visitorHost) { System.out.println(visitorHost.getClass()); } }); } } This makes a ConcreteVisitable which inherits the accept method from AbstractVisitable. In c++, I would consider this risky, since this in AbstractVisitable could be referencing to AbstractVisitable::this, and not ConcreteVisitable::this. I was worried that the code under certain circumstances would print class AbstractVisible. Yet the code above outputs class ConcreteVisitable, even though I hid the real type behind a dynamic proxy (the most difficult case I could come up with). Is the abstract visitor approach above guaranteed to work, or are there some pitfalls with this approach? What guarantees are given in Java with respect to the this pointer?

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• How to catch an incomming text message

  - by Espen

  Hi! I want to be able to control incoming text messages. My application is still on a "proof of concept" version and I'm trying to learn Android programming as I go. First my application need to catch incomming text messages. And if the message is from a known number then deal with it. If not, then send the message as nothing has happened to the default text message application. I have no doubt it can be done, but I still have some concern and I see some pitfalls at how things are done on Android. So getting the incomming text message could be fairly easy - except when there are other messaging applications installed and maybe the user wants to have normal text messages to pop up on one of them - and it will, after my application has had a look at it first. How to be sure my application get first pick of incomming text messages? And after that I need to send most text messages through to any other text message application the user has chosen so the user can actually read the message my application didn't need. Since Android uses intents that are relative at best, I don't see how I can enforce my application to get a peek at all incomming text messages, and then stop it or send it through to the default text messaging application...

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