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• Keyboard for programming

  - by exhuma

  This may seem a bit a tangential topic. It's not directly related to actual code, but is important for our line of work nevertheless. Over the years, I've switched keyboards a few times. All of them had slightly different key layouts. And I'm not talking about the language/locale layout, but the physical layout! Why not the locale layout? Well, quite frankly, that's easy to change via software. I personally have a German keyboard but have it set to the UK layout. Why? It's quite hard to find different layouts in the shops where I live. Even ordering is not always easy in the shops. So that leaves me with Internet shops. But I prefer to "test" my keyboards before buying. The most notable changes are: Mangled "Home Key Block" I've seen this first on a Logitech keyboard, but it may have originated elsewhere. Shape of the "Enter" key I've seen three different cases so far: Two lines high, wider at the top Two lines high, wider at the bottom One line high Shape of the Backspace button I've seen two types so far: One "character" wide Two "characters" wide OS Keys For Macs, you have the Option and Command buttons, for Windows you have the Windows and Context Menu buttons. Cherry even produced a Linux keyboard once (unfortunately I cannot find many details except news results). I assume a dedicated Linux keyboard would sport a Compose key and had the SysRq always labelled as well (note that some standard layouts do this already). Obviously... .. all these differences entail that some keys have to be moved around the board a lot. Which means, if you are used to one and have to work on another one, you happen to hit the wrong keys quite often. As it happens, this is much more annoying for programmers as it is for people who write texts. Mainly because the keys which are moved around are special character keys, often used in programming. Often these hardware layouts depend also indirectly on where you buy the keyboards. Honestly, I haven't seen a keyboard with a one-line "Enter" key in Germany, nor Luxembourg. I may just have missed it but that's how it looks to me at least. A survey I've seen some attempts at surveys in the style "which keyboard is best for programming". But they all - in my opinion - are not using comparable sets. So I was wondering if it was possible to concoct a survey taking the above criteria into account. But ignoring key dimensions that one would be a bit overkill I guess ;) From what I can see there are the following types of physical layout: Backspace: 2-characters wide Enter: 2-Lines, wider top Backspace: 2-characters wide Enter: 1-Line Backspace: 1-character wide Enter: 2-Lines, wider bottom Then there are the other possible permutations (home-key block, os-keys), which in total makes for quite a large list of categories. Now, I wonder... Would anyone be interested in such a survey? I personally would. Because I am looking for the perfect fit for me. If yes, then I could really use the help of anyone here to propose some models to include in the survey. Once I have some models for each category (I'd say at least 3 per category) I could go ahead and write up a survey, put it on-line and let the it collect data for a while. What do you think?

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• Cannot Logout of Facebook with Facebook C# SDK

  - by Ryan Smyth

  I think I've read just about everything out there on the topic of logging out of Facebook inside of a Desktop application. Nothing so far works. Specifically, I would like to log the user out so that they can switch identities, e.g. People sharing a computer at home could then use the software with their own Facebook accounts, but with no chance to switch accounts, it's quite messy. (Have not yet tested switching Windows users accounts as that is simply far too much to ask of the end user and should not be necessary.) Now, I should say that I have set the application to use these permissions: string[] permissions = new string[] { "user_photos", "publish_stream", "offline_access" }; So, "offline_access" is included there. I do not know if this does/should affect logging out or not. Again, my purpose for logging out is merely to switch users. (If there's a better approach, please let me know.) The purported solutions seem to be: Use the JavaScript SDK (FB.logout()) Use "m.facebook.com" instead Create your own URL (and possibly use m.facebook.com) Create your own URL and use the session variable (in ASP.NET) The first is kind of silly. Why resort to JavaScript when you're using C#? It's kind of a step backwards and has a lot of additional overhead in a desktop application. (I have not tried this as it's simply disgustingly messy to do this in a desktop application.) If anyone can confirm that this is the only working method, please do so. I'm desperately trying to avoid it. The second doesn't work. Perhaps it worked in the past, but my umpteen attempts to get it to work have all failed. The third doesn't work. I've tried umpteen dozen variations with zero success. The last option there doesn't work for a desktop application because it's not ASP.NET and you don't have a session variable to work with. The Facebook C# SDK logout also no longer works. i.e. public FacebookLoginDialog(string appId, string[] extendedPermissions, bool logout) { IDictionary<string, object> loginParameters = new Dictionary<string, object> { { "response_type", "token" }, { "display", "popup" } }; _navigateUri = FacebookOAuthClient.GetLoginUrl(appId, null, extendedPermissions, logout, loginParameters); InitializeComponent(); } I remember it working in the past, but it no longer works now. (Which truly puzzles me...) It instead now directs the user to the Facebook mobile page, where the user must manually logout. Now, I could do browser automation to automatically click the logout link for the user, however, this is prone to breaking if Facebook updates the mobile UI. It is also messy, and possibly a worse solution than trying to use the JavaScript SDK FB.logout() method (though not by much). I have searched for some kind of documentation, however, I cannot find anything in the Facebook developer documentation that illustrates how to logout an application. Has anyone solved this problem, or seen any documentation that can be ported to work with the Facebook C# SDK? I am certainly open to using a WebClient or HttpClient/Response if anyone can point to some documentation that could work with it. I simply have not been able to find any low-level documentation that shows how this approach could work. Thank you in advance for any advice, pointers, or links.

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• How to eliminate NULL fields in TSQL

  - by salvationishere

  I am developing a TSQL query in SSMS 2008 R2. I am trying to develop this query to identify one record / client. Because some of these values are NULL, I am currently doing LEFT JOINS on most of the tables. But the problem with the LEFT JOINs is that now I get 1 record for some clients. But if I change this to INNER JOINs then some clients are excluded entirely because they have NULL values for these columns. How do I limit the query result to just one record / client regardless of NULL values? And if there are non-NULL values then I want it to choose the record with non-NULL values. Here is some of my current output: group_profile_id profile_name license_number is_accepting is_accepting_placement managing_office region vendor_name vendor_id applicant_type Office Address status_description Cert Date2 race ethnicity_desc religion 9CD932F1-6BE1-4F80-AB81-0CE32C565BCF Atreides Foster Home 1 Atreides1 1 Yes Manchester, NH Gulf Atlantic Atreides1 00000007 Treatment Foster Home 4042 Arrakis Avenue, Springfield, VT 05156 Open/Re-opened 2011-06-01 00:00:00.000 NULL NULL NULL DCE354D5-A7CC-409F-B5A3-89BF664B7718 Averitte, Leon and Sandra 00000044 1 Yes Birmingham, AL Gulf Atlantic AL Averitte, Leon and Sandra 00000044 Treatment Foster Home 3816 5th Avenue, Bessemer, AL 35020, (205)482-4307 Open/Re-opened 2011-08-05 00:00:00.000 NULL NULL NULL DCE354D5-A7CC-409F-B5A3-89BF664B7718 Averitte, Leon and Sandra 00000044 1 Yes Birmingham, AL Gulf Atlantic AL Averitte, Leon and Sandra 00000044 Treatment Foster Home 3816 5th Avenue, Bessemer, AL 35020, (205)482-4307 Open/Re-opened 2011-08-05 00:00:00.000 Caucasian/White Non Hispanic NULL AD02A43C-6F38-4F35-8C9E-E12422690BFB Bass, Matthew and Sarah 00000076 1 Yes Jacks on, MS Central Gulf Coast MS Bass, Matthew and Sarah 00000076 Treatment Foster Home 506 Eagelwood Drive, Florence, MS 39073, (601)665-7169 Open/Re-opened 2011-04-01 00:00:00.000 NULL NULL NULL AD02A43C-6F38-4F35-8C9E-E12422690BFB Bass, Matthew and Sarah 00000076 1 Yes Jackson, MS Central Gulf Coast MS Bass, Matthew and Sarah 00000076 Treatment Foster Home 506 Eagelwood Drive, Florence, MS 39073, (601)665-7169 Open/Re-opened 2011-04-01 00:00:00.000 Caucasian/White NULL Baptist You can see that both Averitte and Bass profile names have one record with NULL race, ethnicity, religion. How do I eliminate these rows (rows 2 and 4)? Here is my query currently: select distinct gp.group_profile_id, gp.profile_name, gp.license_number, gp.is_accepting, case when gp.is_accepting = 1 then 'Yes' when gp.is_accepting = 0 then 'No ' end as is_accepting_placement, mo.profile_name as managing_office, regions.[region_description] as region, pv.vendor_name, pv.id as vendor_id, at.description as applicant_type, dbo.GetGroupAddress(gp.group_profile_id, null, 0) as [Office Address], gsv.status_description, ri.[description] as race, ethnicity.description as ethnicity_desc, religion.description as religion from group_profile gp With (NoLock) --Office Information inner join group_profile_type gpt With (NoLock) on gp.group_profile_type_id = gpt.group_profile_type_id and gpt.type_code = 'FOSTERHOME' and gp.agency_id = @agency_id and gp.is_deleted = 0 inner join group_profile mo With (NoLock) on gp.managing_office_id = mo.group_profile_id left outer join payor_vendor pv With (NoLock) on gp.payor_vendor_id = pv.payor_vendor_id left outer join applicant_type at With (NoLock) on gp.applicant_type_id = at.applicant_type_id and at.is_foster_home = 1 inner join group_status_view gsv With (NoLock) on gp.group_profile_id = gsv.group_profile_id and gsv.status_value = 'OPEN' and gsv.effective_date = (Select max(b.effective_date) from group_status_view b With (NoLock) where gp.group_profile_id = b.group_profile_id) left outer join regions With (NoLock) on isnull(mo.regions_id, gp.regions_id) = regions.regions_id left join enrollment en on en.group_profile_id = gp.group_profile_id join event_log el on el.event_log_id = en.event_log_id left join people client on client.people_id = el.people_id left join race With (NoLock) on el.people_id = race.people_id left join group_profile_race gpr with (nolock) on gpr.race_info_id = race.race_info_id left join race_info ri with (nolock) on ri.race_info_id = gpr.race_info_id left join ethnicity With(NoLock) On client.ethnicity = ethnicity.ethnicity_id left join religion on client.religion = religion.religion_id

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• How do you stop scripters from slamming your website hundreds of times a second?

  - by davebug

  [update] I've accepted an answer, as lc deserves the bounty due to the well thought-out answer, but sadly, I believe we're stuck with our original worst case scenario: CAPTCHA everyone on purchase attempts of the crap. Short explanation: caching / web farms make it impossible for us to actually track hits, and any workaround (sending a non-cached web-beacon, writing to a unified table, etc.) slows the site down worse than the bots would. There is likely some pricey bit of hardware from Cisco or the like that can help at a high level, but it's hard to justify the cost if CAPTCHAing everyone is an alternative. I'll attempt to do a more full explanation in here later, as well as cleaning this up for future searchers (though others are welcome to try, as it's community wiki). I've added bounty to this question and attempted to explain why the current answers don't fit our needs. First, though, thanks to all of you who have thought about this, it's amazing to have this collective intelligence to help work through seemingly impossible problems. I'll be a little more clear than I was before: This is about the bag o' crap sales on woot.com. I'm the president of Woot Workshop, the subsidiary of Woot that does the design, writes the product descriptions, podcasts, blog posts, and moderates the forums. I work in the css/html world and am only barely familiar with the rest of the developer world. I work closely with the developers and have talked through all of the answers here (and many other ideas we've had). Usability of the site is a massive part of my job, and making the site exciting and fun is most of the rest of it. That's where the three goals below derive. CAPTCHA harms usability, and bots steal the fun and excitement out of our crap sales. To set up the scenario a little more, bots are slamming our front page tens of times a second screenscraping (and/or scanning our rss) for the Random Crap sale. The moment they see that, it triggers a second stage of the program that logs in, clicks I want One, fills out the form, and buys the crap. In current (2/6/2009) order of votes: lc: On stackoverflow and other sites that use this method, they're almost always dealing with authenticated (logged in) users, because the task being attempted requires that. On Woot, anonymous (non-logged) users can view our home page. In other words, the slamming bots can be non-authenticated (and essentially non-trackable except by IP address). So we're back to scanning for IPs, which a) is fairly useless in this age of cloud networking and spambot zombies and b) catches too many innocents given the number of businesses that come from one IP address (not to mention the issues with non-static IP ISPs and potential performance hits to trying to track this). Oh, and having people call us would be the worst possible scenario. Can we have them call you? BradC Ned Batchelder's methods look pretty cool, but they're pretty firmly designed to defeat bots built for a network of sites. Our problem is bots are built specifically to defeat our site. Some of these methods could likely work for a short time until the scripters evolved their bots to ignore the honeypot, screenscrape for nearby label names instead of form ids, and use a javascript-capable browser control. lc again "Unless, of course, the hype is part of you

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• MovieClip, counter almost working AS3

  - by VideoDnd

  How do I get my counter to work? This was over my director's head. Please include explanation, and feel free to comment. CONFUSION: I'm confused about the MovieClip container in as3. public class NumbersView extends MovieClip, so that seems to be a container. That may not be the problem, but that's where I got lost. CODE http://videodnd.weebly.com/ The working version of this code is fantastic. My code bellow is an attempt at revising it. The source has been adapted from various smart people. It's a work in progress LIBRARY OBJECT 'vertical number column' Name: mc-NumberImage Class: NumberImage OUTPUT ERRORS 'When I uncomment the code" 1023: Incompatible override. NumbersView... 1021: Duplicate function definition. NumbersView... //NUMBER DOCUMENT CLASS //IMPORT import flash.display.Sprite; import flash.events.Event; import flash.utils.Timer; import flash.events.TimerEvent; import flash.display.DisplayObject; import flash.display.MovieClip; import flash.utils.Dictionary; import caurina.transitions.Tweener; //COUNTER var timer:Timer = new Timer(1000); var count:int = 0; var fcount:int = 0; timer.addEventListener(TimerEvent.TIMER, incrementCounter); timer.start(); function incrementCounter(event:TimerEvent) { count++; fcount=int(count*count/1000); } function formatCount(i:int):String { var fraction:int = i % 100; var whole:int = i / 100; return ("000000000" + i).substr(-9, 9); } //------------------------------------------------------------------------ //PROBLEM AREA function enterFrameHandler(e:Event):void { // numbers.setTime(formatCount(fcount)); } var _listItems:Array = new Array(); var previousNums:Array; const numHeight:int = 120; var NumbersView:Sprite = new Sprite(); //var numbers:NumbersView = new NumbersView; //NUMBERSVIEW // function NumbersView($n:int):void { _listItems = new Array(); previousNums = new Array(); var item:NumberImage; var offset:int = _listItems.length; for (var i:Number = 0; i < 9; i++) { item = new NumberImage(); // }//<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< //------------------------------------------------------------------------ //PUSH ARRAY addChild(item); item.x = i * item.width; _listItems.push(item); } //TWEENER 'Y SCROLLING' function setTime($number:String):void { var nums:Array = $number.split(""); for (var i:Number = 0; i < nums.length; i++) { if (nums[i] == previousNums[i]) continue; Tweener.removeTweens(_listItems[i]); var newY:int = int(nums[i]) * -numHeight; if (_listItems[i].y < 0) _listItems[i].y = numHeight; Tweener.addTween(_listItems[i], { y:newY, time:3 } ); } previousNums = nums; } D E S C R I P T I O N COUNTER: formatCount needs to get passed to Tweener STAGE: for loop, sets up children to be added to the stage NumbersView becomes item, item array adds children to stage TWEENER: advances the vertical number column every time the count fires adds and removes WHY - Learning - Benifit in simplifying the classes and putting it in one FLA

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• Rails routing to XML/JSON without views gone mad

  - by John Schulze

  I have a mystifying problem. In a very simple Ruby app i have three classes: Drivers, Jobs and Vehicles. All three classes only consist of Id and Name. All three classes have the same #index and #show methods and only render in JSON or XML (this is in fact true for all their CRUD methods, they are identical in everything but name). There are no views. For example: def index @drivers= Driver.all respond_to do |format| format.js { render :json => @drivers} format.xml { render :xml => @drivers} end end def show @driver = Driver.find(params[:id]) respond_to do |format| format.js { render :json => @driver} format.xml { render :xml => @driver} end end The models are similarly minimalistic and only contain: class Driver< ActiveRecord::Base validates_presence_of :name end In routes.rb I have: map.resources :drivers map.resources :jobs map.resources :vehicles map.connect ':controller/:action/:id' map.connect ':controller/:action/:id.:format' I can perform POST/create, GET/index and PUT/update on all three classes and GET/read used to work as well until I installed the "has many polymorphs" ActiveRecord plugin and added to environment.rb: require File.join(File.dirname(__FILE__), 'boot') require 'has_many_polymorphs' require 'active_support' Now for two of the three classes I cannot do a read any more. If i go to localhost:3000/drivers they all list nicely in XML but if i go to localhost:3000/drivers/3 I get an error: Processing DriversController#show (for 127.0.0.1 at 2009-06-11 20:34:03) [GET] Parameters: {"id"=>"3"} [4;36;1mDriver Load (0.0ms)[0m [0;1mSELECT * FROM "drivers" WHERE ("drivers"."id" = 3) [0m ActionView::MissingTemplate (Missing template drivers/show.erb in view path app/views): app/controllers/drivers_controller.rb:14:in `show' ...etc This is followed a by another unexpected error: Processing ApplicationController#show (for 127.0.0.1 at 2009-06-11 21:35:52)[GET] Parameters: {"id"=>"3"} NameError (uninitialized constant ApplicationController::AreaAccessDenied): ...etc What is going on here? Why does the same code work for one class but not the other two? Why is it trying to do a #view on the ApplicationController? I found that if I create a simple HTML view for each of the three classes these work fine. To each class I add: format.html # show.html.erb With this in place, going to localhost:3000/drivers/3 renders out the item in HTML and I get no errors in the log. But if attach .xml to the URL it again fails for two of the classes (with the same error message as before) while one will output XML as expected. Even stranger, on the two failing classes, when adding .js to the URL (to trigger JSON rendering) I get the HTML output instead! Is it possible this has something to do with the "has many polymorphs" plugin? I have heard of people having routing issues after installing it. Removing "has many polymorphs" and "active support" from environment.rb (and rebooting the sever) seems to make no difference whatsoever. Yet my problems started after it was installed. I've spent a number of hours on this problem now and am starting to get a little desperate, Google turns up virtually no information which makes me suspect I must have missed something elementary. Any enlightenment or hint gratefully received! JS

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• What do I need to write a small game on Linux?

  - by Michas

  I want to make a simple game: 2d, single-player, without tons of animations and special effects. I am not interested in ready to use game engines, I want to learn to write some code in a quite universal language. I am using Linux (AMD64) and looking for something easy with nice library for games. I do not want to mix few languages, most of them are in fact fast enough themselves for my needs. Cross platform would be an advantage, however all I need is a good Linux support. I have been considering few solutions. Ruby + Language looks very nice. + I am going to learn Ruby. - I am afraid I can have problems with additional libraries. - This thread about game libraries for Ruby could be longer. SDL + C + It is used for games. + It is very easy to set up. + There is a lot of additional libraries. + It is cross-platform. - The solution is quite low level. - The language is sometimes quite hard to read. QT + C++ + It is very easy to set up. + The standard QT libraries supports everything I can possibly need. + It is cross-platform. + The documentation is good. - The compilation is slow. - The language looks horrible. - The size of standard QT libraries is too big to comprehend. Environment of web browser + I am going to learn something more about this environment. + It is somewhat used for games. + It is quite cross-platform. - It would be too much experimental. Java + It is used for games. + The standard Java libraries supports everything I can possibly need. + It is cross-platform. - It is quite hard to set up. - The size of standard Java libraries is too big to comprehend. - The source code in Java could look better. - I think I do not want to learn Java. Google Go + I am going to learn Google Go. - There is big problem with libraries. - The solution would be quite low level. Python + It looks some people do games in Python, according to this thread. + It looks there are probably more libraries than for Ruby. - The Ruby language looks better. - I think I do not want to learn Python. C++ + something else + It is used for games. + It would be probably cross-platform. + There is a lot of libraries. - I do not need C++ extensions over C. - Compilation could be slow, there are fast compilers for C, not for C++. Haskell + I am going to learn Haskell. - Many things about programming computer games looks too much imperative. - It looks I can have some problems with libraries. - Compilation (GHC) looks slow. There is probably something more to consider. Does anyone have experience in making small games for Linux in non mainstream solutions? Does anyone have an advice for me?

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• Evidence-Based-Scheduling - are estimations only as accurate as the work-plan they're based on?

  - by Assaf Lavie

  I've been using FogBugz's Evidence Based Scheduling (for the uninitiated, Joel explains) for a while now and there's an inherent problem I can't seem to work around. The system is good at telling me the probability that a given project will be delivered at some date, given the detailed list of tasks that comprise the project. However, it does not take into account the fact that during development additional tasks always pop up. Now, there's the garbage-can approach of creating a generic task/scheduled-item for "last minute hacks" or "integration tasks", or what have you, but that clearly goes against the idea of aggregating the estimates of many small cases. It's often the case that during the development stage of a project you realize that there's a whole area your planning didn't cover, because, well, that's the nature of developing stuff that hasn't been developed before. So now your ~3 month project may very well turn into a 6 month project, but not because your estimations were off (you could be the best estimator in the world, for those task the comprised your initial work plan); rather because you ended up adding a whole bunch of new tasks that weren't there to begin with. EBS doesn't help you with that. It could, theoretically (I guess). It could, perhaps, measure the amount of work you add to a project over time and take that into consideration when estimating the time remaining on a given project. Just a thought. In other words, EBS works on a task basis, but not on a project/release basis - but the latter is what's important. It's what your boss typically cares about - delivery date, not the time it takes to finish each task along the way, and not the time it would have taken, if your planning was perfect. So the question is (yes, there's a question here, don't close it): What's your methodology when it comes to using EBS in FogBugz and how do you solve the problem above, which seems to be a main cause of schedule delays and mispredictions? Edit Some more thoughts after reading a few answers: If it comes down to having to choose which delivery date you're comfortable presenting to your higher-ups by squinting at the delivery-probability graph and choosing 80%, or 95%, or 60% (based on what, exactly?) then we've resorted to plain old buffering/factoring of our estimates. In which case, couldn't we have skipped the meticulous case by case hour-sized estimation effort step? By forcing ourselves to break down tasks that take more than a day into smaller chunks of work haven't we just deluded ourselves into thinking our planning is as tight and thorough as it could be? People may be consistently bad estimators that do not even learn from their past mistakes. In that respect, having an EBS system is certainly better than not having one. But what can we do about the fact that we're not that good in planning as well? I'm not sure it's a problem that can be solved by a similar system. Our estimates are wrong because of tendencies to be overly optimistic/pessimistic about certain tasks, and because of neglect to account for systematic delays (e.g. sick days, major bug crisis) - and usually not because we lack knowledge about the work that needs to be done. Our planning, on the other hand, is often incomplete because we simply don't have enough knowledge in this early stage; and I don't see how an EBS-like system could fill that gap. So we're back to methodology. We need to find a way to accommodate bad or incomplete work plans that's better than voodoo-multiplication.

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• NHibernate Proxy Creation

  - by Chris Meek

  I have a class structure like the following class Container { public virtual int Id { get; set; } public IList<Base> Bases { get; set; } } class Base { public virtual int Id { get; set; } public virtual string Name { get; set; } } class EnemyBase : Base { public virtual int EstimatedSize { get; set; } } class FriendlyBase : Base { public virtual int ActualSize { get; set; } } Now when I ask the session for a particular Container it normally gives me the concrete EnemyBase and FriendlyBase objects in the Bases collection. I can then (if I so choose) cast them to their concrete types and do something specific with them. However, sometime I get a proxy of the "Base" class which is not castable to the concrete types. The same method is used both times with the only exception being that in the case that I get proxies I have added some related entities to the session (think the friendly base having a collection of people or something like that). Is there any way I can prevent it from doing the proxy creating and why would it choose to do this in some scenarios? UPDATE The mappings are generated with the automap feature of fluentnhibernate but look something like this when exported <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true"> <class xmlns="urn:nhibernate-mapping-2.2" mutable="true" name="Base" table="`Base`"> <id name="Id" type="System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="Id" /> <generator class="MyIdGenerator" /> </id> <property name="Name" type="String"> <column name="Name" /> </property> <joined-subclass name="EnemyBase"> <key> <column name="Id" /> </key> <property name="EstimatedSize" type="Int"> <column name="EstimatedSize" /> </property> </joined-subclass> <joined-subclass name="FriendlyBase"> <key> <column name="Id" /> </key> <property name="ActualSize" type="Int"> <column name="ActualSize" /> </property> </joined-subclass> </class> </hibernate-mapping> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true"> <class xmlns="urn:nhibernate-mapping-2.2" mutable="true" name="Container" table="`Container`"> <id name="Id" type="System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"> <column name="Id" /> <generator class="MyIdGenerator" /> </id> <bag cascade="all-delete-orphan" inverse="true" lazy="false" name="Bases" mutable="true"> <key> <column name="ContainerId" /> </key> <one-to-many class="Base" /> </bag> </class> </hibernate-mapping>

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• Forcing a transaction to rollback on validation errors in Seam

  - by Chris Williams

  Quick version: We're looking for a way to force a transaction to rollback when specific situations occur during the execution of a method on a backing bean but we'd like the rollback to happen without having to show the user a generic 500 error page. Instead, we'd like the user to see the form she just submitted and a FacesMessage that indicates what the problem was. Long version: We've got a few backing beans that use components to perform a few related operations in the database (using JPA/Hibernate). During the process, an error can occur after some of the database operations have happened. This could be for a few different reasons but for this question, let's assume there's been a validation error that is detected after some DB writes have happened that weren't detectible before the writes occurred. When this happens, we'd like to make sure all of the db changes up to this point will be rolled back. Seam can deal with this because if you throw a RuntimeException out of the current FacesRequest, Seam will rollback the current transaction. The problem with this is that the user is shown a generic error page. In our case, we'd actually like the user to be shown the page she was on with a descriptive message about what went wrong, and have the opportunity to correct the bad input that caused the problem. The solution we've come up with is to throw an Exception from the component that discovers the validation problem with the annotation: @ApplicationException( rollback = true ) Then our backing bean can catch this exception, assume the component that threw it has published the appropriate FacesMessage, and simply return null to take the user back to the input page with the error displayed. The ApplicationException annotation tells Seam to rollback the transaction and we're not showing the user a generic error page. This worked well for the first place we used it that happened to only be doing inserts. The second place we tried to use it, we have to delete something during the process. In this second case, everything works if there's no validation error. If a validation error does happen, the rollback Exception is thrown and the transaction is marked for rollback. Even if no database modifications have happened to be rolled back, when the user fixes the bad data and re-submits the page, we're getting: java.lang.IllegalArgumentException: Removing a detached instance The detached instance is lazily loaded from another object (there's a many to one relationship). That parent object is loaded when the backing bean is instantiated. Because the transaction was rolled back after the validation error, the object is now detached. Our next step was to change this page from conversation scope to page scope. When we did this, Seam can't even render the page after the validation error because our page has to hit the DB to render and the transaction has been marked for rollback. So my question is: how are other people dealing with handling errors cleanly and properly managing transactions at the same time? Better yet, I'd love to be able to use everything we have now if someone can spot something I'm doing wrong that would be relatively easy to fix. I've read the Seam Framework article on Unified error page and exception handling but this is geared more towards more generic errors your application might encounter.

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• Delphi 5: Ideas for simulating "Obsolete" or "Deprecated" methods?

  - by Ian Boyd

  i want to mark a method as obsolete, but Delphi 5 doesn't have such a feature. For the sake of an example, here is a made-up method with it's deprecated and new preferred form: procedure TStormPeaksQuest.BlowHodirsHorn; overload; //obsolete procedure TStormPeaksQuest.BlowHodirsHorn(UseProtection: Boolean); overload; Note: For this hypothetical example, we assume that using the parameterless version is just plain bad. There are problems with not "using protection" - which have no good solution. Nobody likes having to use protection, but nobody wants to not use protection. So we make the caller decide if they want to use protection or not when blowing Hodir's horn. If we default the parameterless version to continue not using protection: procedure TStormPeaksQuest.BlowHodirsHorn; begin BlowHodirsHorn(False); //No protection. Bad! end; then the developer is at risk of all kinds of nasty stuff. If we force the parameterless version to use protection: procedure TStormPeaksQuest.BlowHodirsHorn; begin BlowHodirsHorn(True); //Use protection; crash if there isn't any end; then there's a potential for problems if the developer didn't get any protection, or doesn't own any. Now i could rename the obsolete method: procedure TStormPeaksQuest.BlowHodirsHorn_Deprecatedd; overload; //obsolete procedure TStormPeaksQuest.BlowHodirsHorn(UseProtection: Boolean); overload; But that will cause a compile error, and people will bitch at me (and i really don't want to hear their whining). i want them to get a nag, rather than an actual error. i thought about adding an assertion: procedure TStormPeaksQuest.BlowHodirsHorn; //obsolete begin Assert(false, 'TStormPeaksQuest.BlowHodirsHorn is deprecated. Use BlowHodirsHorn(Boolean)'); ... end; But i cannot guarantee that the developer won't ship a version without assertions, causing a nasty crash for the customer. i thought about using only throwing an assertion if the developer is debugging: procedure TStormPeaksQuest.BlowHodirsHorn; //obsolete begin if DebugHook > 0 then Assert(false, 'TStormPeaksQuest.BlowHodirsHorn is deprecated. Use BlowHodirsHorn(Boolean)'); ... end; But i really don't want to be causing a crash at all. i thought of showing a MessageDlg if they're in the debugger (which is a technique i've done in the past): procedure TStormPeaksQuest.BlowHodirsHorn; //obsolete begin if DebugHook > 0 then MessageDlg('TStormPeaksQuest.BlowHodirsHorn is deprecated. Use BlowHodirsHorn(Boolean)', mtWarning, [mbOk], 0); ... end; but that is still too disruptive. And it has caused problems where the code is stuck at showing a modal dialog, but the dialog box wasn't obviously visible. i was hoping for some sort of warning message that will sit there nagging them - until they gouge their eyes out and finally change their code. i thought perhaps if i added an unused variable: procedure TStormPeaksQuest.BlowHodirsHorn; //obsolete var ThisMethodIsObsolete: Boolean; begin ... end; i was hoping this would cause a hint only if someone referenced the code. But Delphi shows a hint even if you don't call actually use the obsolete method. Can anyone think of anything else?

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• Design Question - how do you break the dependency between classes using an interface?

  - by Seth Spearman

  Hello, I apologize in advance but this will be a long question. I'm stuck. I am trying to learn unit testing, C#, and design patterns - all at once. (Maybe that's my problem.) As such I am reading the Art of Unit Testing (Osherove), and Clean Code (Martin), and Head First Design Patterns (O'Reilly). I am just now beginning to understand delegates and events (which you would see if you were to troll my SO questions of recent). I still don't quite get lambdas. To contextualize all of this I have given myself a learning project I am calling goAlarms. I have an Alarm class with members you'd expect (NextAlarmTime, Name, AlarmGroup, Event Trigger etc.) I wanted the "Timer" of the alarm to be extensible so I created an IAlarmScheduler interface as follows... public interface AlarmScheduler { Dictionary<string,Alarm> AlarmList { get; } void Startup(); void Shutdown(); void AddTrigger(string triggerName, string groupName, Alarm alarm); void RemoveTrigger(string triggerName); void PauseTrigger(string triggerName); void ResumeTrigger(string triggerName); void PauseTriggerGroup(string groupName); void ResumeTriggerGroup(string groupName); void SetSnoozeTrigger(string triggerName, int duration); void SetNextOccurrence (string triggerName, DateTime nextOccurrence); } This IAlarmScheduler interface define a component that will RAISE an alarm (Trigger) which will bubble up to my Alarm class and raise the Trigger Event of the alarm itself. It is essentially the "Timer" component. I have found that the Quartz.net component is perfectly suited for this so I have created a QuartzAlarmScheduler class which implements IAlarmScheduler. All that is fine. My problem is that the Alarm class is abstract and I want to create a lot of different KINDS of alarm. For example, I already have a Heartbeat alarm (triggered every (int) interval of minutes), AppointmentAlarm (triggered on set date and time), Daily Alarm (triggered every day at X) and perhaps others. And Quartz.NET is perfectly suited to handle this. My problem is a design problem. I want to be able to instantiate an alarm of any kind without my Alarm class (or any derived classes) knowing anything about Quartz. The problem is that Quartz has awesome factories that return just the right setup for the Triggers that will be needed by my Alarm classes. So, for example, I can get a Quartz trigger by using TriggerUtils.MakeMinutelyTrigger to create a trigger for the heartbeat alarm described above. Or TriggerUtils.MakeDailyTrigger for the daily alarm. I guess I could sum it up this way. Indirectly or directly I want my alarm classes to be able to consume the TriggerUtils.Make* classes without knowing anything about them. I know that is a contradiction, but that is why I am asking the question. I thought about putting a delegate field into the alarm which would be assigned one of these Make method but by doing that I am creating a hard dependency between alarm and Quartz which I want to avoid for both unit testing purposes and design purposes. I thought of using a switch for the type in QuartzAlarmScheduler per here but I know it is bad design and I am trying to learn good design. If I may editorialize a bit. I've decided that coding (predefined) classes is easy. Design is HARD...in fact, really hard and I am really fighting feeling stupid right now. I guess I want to know if you really smart people took a while to really understand and master this stuff or should I feel stupid (as I do) because I haven't grasped it better in the couple of weeks/months I have been studying. You guys are awesome and thanks in advance for your answers. Seth

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• vertical navigation that shows hidden submenu on click using JQuery

  - by user346602

  Hi, I am trying to make a menu that works like the one on this flash site: http://elevensix.de/ When I click "portfolio", only then to the subnavigation links reveal themselves. Right now I have only managed to get a typical vertical "reveal subnavigation on hover menu" working. What is required is that once the appropriate menu item it cicked, its submenu shows. This submenu remains revealed as the submenu items are hovered over then selected. When the submenu item is selected, the content shows, and both the menu and submenu remain visible (the selected menu and submenu item are given a distinct colour to show the navigation path). Whew. Here is my html: <div id="nav"> <ul> <li><a href="#">about</a></li> <li><a href="#">testimonials</a> <ul> <li><a href="#">testimonial1</a></li> <li><a href="#">testimonial2</a></li> <li><a href="#">testimonial3</a></li> <li><a href="#">testimonial4</a></li> </ul> </li> <li><a href="#">Services</a> <ul> <li><a href="#">services1</a></li> <li><a href="#">services2</a></li> <li><a href="#">services3</a></li> <li><a href="#">services4</a></li> </ul> </li> <li><a href="#">Gallery</a></li> <li><a href="#">Contact</a></li> </ul> </div><!--end #nav--> and here is my css: #nav { width:160px; position: relative; top: 250px; left: 20px; } #nav ul { margin:0px; padding:0px; } #nav ul li { line-height:24px; list-style:none; } #nav a { text-decoration: none; color: #9d9fa2; } #nav ul li a:hover { position:relative; color: #00aeef; } #nav ul ul { display:none; position:absolute; left:160px; top:4px; } #nav ul li:hover ul { display:block; color: #00aeef; } #nav ul ul li { width:160px; float:left; display:inline; line-height:16px; } .selected { color: #00aeef !important; } Should I be giving the submenus a class so that I can hide then show them? And where would the class be applied? To the ul? could I use the same class for both submenus? Am I wrong in how I am applying the display:none values for this purpose? Many thanks to all the clever people on here.

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• Setting value for autocomplete search field linked to Google Places API

  - by user1653350

  I have a web page where people will be able to enter multiple destinations. When they state they want to enter a new destination, the current field values are stored in arrays. If they choose to go back to a previous destination, the relevant values are reinserted into the form fields. I am using the search field linked to autocomplete as the visible display of the destination. When I attempt to put a value into the linked search field, the value is presented as if it is a placeholder instead of a value. Enter the field and the value is removed by the onFocus() event of the Google Places autocomplete add-in. How can I reinsert the value and have it recognised as a value instead of placeholder. field definition in the form <label for="GoogleDestSrch" class="inputText">Destination: <span id="DestinationDisplay2">1</span> <span class="required"><font size="5"> * </font></span></label> <input id="GoogleDestSrch" type="text" size="50" placeholder="Please enter your destination" /> initialise code for Google Places API listener var input = document.getElementById('GoogleDestSrch'); var autocomplete = new google.maps.places.Autocomplete(input); google.maps.event.addListener(autocomplete, 'place_changed', function() { fillInAddress(); }); attempting to reinsert value into search field when prior destination reloaded form.GoogleDestSrch.value = GoogleDestSrch[index]; Issue With Google Places <script language="JavaScript" type="text/javascript"> function GotoDestination(index) { var domove = true; if (index == 0) { index = lastIndex + 1; } else { if (index == -1) { index = lastIndex - 1; if (index == 0) { index = 1; domove = false; } } } if (domove) { if (index != lastIndex) { var doc = window.document; var pdbutton = doc.getElementById("pdbutton"); var pdbutton1 = doc.getElementById("pdbutton1"); if ((index > lastIndex)) { // move to next destination saveDataF(lastIndex); loadDataF(index); lastIndex = index; } else if (index <= lastIndex) { // move to previous destination saveDataF(lastIndex); loadDataF(index); lastIndex = index; } } } } var input; var autocomplete; // fill in the Google metadata when a destination is selected function fillInAddress() { var strFullValue = ''; var strFullGeoValue = ''; var place = autocomplete.getPlace(); document.getElementById("GoogleType").value = place.types[0]; } function saveDataF(index) { var fieldValue; var blankSearch = "Please enter"; // placeholder text for Google Places fieldValue = document.getElementById("GoogleDestSrch").value; if (fieldValue.indexOf(blankSearch) > -1) { fieldValue = ""; } GoogleDestSrch[index] = fieldValue; } function loadDataF(index) { if ((GoogleDestSrch[index] + "") == "undefined") { document.getElementById("GoogleDestSrch").value = ""; } else { document.getElementById("GoogleDestSrch").value = GoogleDestSrch[index]; } } // -- Destination: 1 * Type of place // input = document.getElementById('GoogleDestSrch'); autocomplete = new google.maps.places.Autocomplete(input); google.maps.event.addListener(autocomplete, 'place_changed', function () { fillInAddress(); }); //]]

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• Hardware/Software inventory open source projects

  - by Dick dastardly

  Dear Stackoverflowers I would like to develop a Network Inventory application that works on any operating system. Reports on every possible resource attacehd to a network. Reports all pertinent details of hardware and software. Thats (and i hate to use the phrase) my "End Game". However I am running before i can crawl here. I have no experience of this type of development, e.g. discovering a computers hardware and software settings. I've spent almost two weeks googling and come up short! :-(. So I am turning to you to ask these questions:- My first step is to find an existing open source project i can incorporate into my own code that extracts the fine grained details i am after, e.g. EVERYTHING there is to know about the hardaware and software on a single machine. Does this project exist? or do i have to develop that first? Have i got to write all this in C? I am guessing getting this information about a computer is going to be easier than for printers, scanners, routers etc... e.g. everything else you would find attached to a network. Once i have access to a single computers details i then need to investigate how i can traverse an entire newtork of printers, scanners, routers, load balancers, switches, firewalls, workstations, servers, storeage devices, laptops, monitors, the list goes on and on One problem i have is i dont have a 1000 machine newtork to play on! Is there any such resource available on theinternet? (is that a silly question?) Anywho, if you dont ask you wont find out! One aspect iam really looking forward to finding out how to travers the entire network, should i be using TCP/IP for this? Whats a good site, blog, usergorup, book for TCP/IP development? How do i go about getting through firewalls? How many questions can i ask in one go? :-) My previous question on this topic ended up with PYTHON being championed as the language/script to go with to develop this application in. Having looked at a few PYTHON examples they all seemed to be related to WINDOWS networks and interrogating Windows Management Instrumentation (WMI). I had the feeling you cant rely on whats in WMI, and even if you can that s no good for UNIX netwrks. Surely there exist common code for extracting hardware and software details from a computer? Why cant i find it on the internet? Pease help? Theres no prizes though :-( Thanks in advance I would like to appologise if i have broken forum rules or not tried hard enough on my own before asking for assistance. I just would like to start moving forward with this as its one of the best projects i have been involved with. I am inspired by the many differnt number of challenges involved and that if i manage to produce a useful application at the end of it it would hopefully be extremely helpful to many people. That sit Thanks in advance DD

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• Getting 500 Error when trying to access Rails application through Apache2

  - by cojones

  Hey, I'm using Apache2 as proxy and mongrel_cluster as server for my Rails applications. When I try to access it by typing in the url I get a 500 "Internal Server Error" but when try to locally access the website with "lynx http://localhost:8200" it works. This is my config: <Proxy balancer://sportfreundewitold_cluster> BalancerMember http://127.0.0.1:8200 BalancerMember http://127.0.0.1:8201 </Proxy> # httpd [example.org] dmn entry BEGIN. <VirtualHost x.x.x.x:80> <IfModule suexec_module> SuexecUserGroup vu2025 vu2025 </IfModule> ServerAdmin [email protected] DocumentRoot /var/www/virtual/example.org/htdocs/current/public ServerName example.org ServerAlias www.example.org example.org *.example.org vu2025.admin.roughneck-media.de Alias /errors /var/www/virtual/example.org/errors/ RedirectMatch permanent ^/ftp[\/]?$ http://admin.roughneck-media.de/ftp/ RedirectMatch permanent ^/pma[\/]?$ http://admin.roughneck-media.de/pma/ RedirectMatch permanent ^/webmail[\/]?$ http://admin.roughneck-media.de/webmail/ RedirectMatch permanent ^/ispcp[\/]?$ http://admin.roughneck-media.de/ ErrorDocument 401 /errors/401.html ErrorDocument 403 /errors/403.html ErrorDocument 404 /errors/404.html ErrorDocument 500 /errors/500.html ErrorDocument 503 /errors/503.html <IfModule mod_cband.c> CBandUser example.org </IfModule> # httpd awstats support BEGIN. # httpd awstats support END. # httpd dmn entry cgi support BEGIN. ScriptAlias /cgi-bin/ /var/www/virtual/example.org/cgi-bin/ <Directory /var/www/virtual/example.org/cgi-bin> AllowOverride AuthConfig #Options ExecCGI Order allow,deny Allow from all </Directory> # httpd dmn entry cgi support END. <Directory /var/www/virtual/example.org/htdocs/current/public> # httpd dmn entry PHP support BEGIN. # httpd dmn entry PHP support END. Options -Indexes Includes FollowSymLinks MultiViews AllowOverride All Order allow,deny Allow from all </Directory> # httpd dmn entry PHP2 support BEGIN. <IfModule mod_php5.c> php_admin_value open_basedir "/var/www/virtual/example.org/:/var/www/virtual/example.org/phptmp/:/usr/share/php/" php_admin_value upload_tmp_dir "/var/www/virtual/example.org/phptmp/" php_admin_value session.save_path "/var/www/virtual/example.org/phptmp/" php_admin_value sendmail_path '/usr/sbin/sendmail -f vu2025 -t -i' </IfModule> <IfModule mod_fastcgi.c> ScriptAlias /php5/ /var/www/fcgi/example.org/ <Directory "/var/www/fcgi/example.org"> AllowOverride None Options +ExecCGI -MultiViews -Indexes Order allow,deny Allow from all </Directory> </IfModule> <IfModule mod_fcgid.c> Include /etc/apache2/mods-available/fcgid_ispcp.conf <Directory /var/www/virtual/example.org/htdocs> FCGIWrapper /var/www/fcgi/example.org/php5-fcgi-starter .php Options +ExecCGI </Directory> <Directory "/var/www/fcgi/example.org"> AllowOverride None Options +ExecCGI MultiViews -Indexes Order allow,deny Allow from all </Directory> </IfModule> # httpd dmn entry PHP2 support END. Include /etc/apache2/ispcp/example.org.conf RewriteEngine On # Make sure people go to www.myapp.com, not myapp.com RewriteCond %{HTTP_HOST} ^myapp\.com$ [NC] RewriteRule ^(.*)$ http://www.myapp.com$1 [R=301,L] # Yes, I've read no-www.com, but my site already has much Google-Fu on # www.blah.com. Feel free to comment this out. # Uncomment for rewrite debugging #RewriteLog logs/myapp_rewrite_log #RewriteLogLevel 9 # Check for maintenance file and redirect all requests RewriteCond %{DOCUMENT_ROOT}/system/maintenance.html -f RewriteCond %{SCRIPT_FILENAME} !maintenance.html RewriteRule ^.*$ /system/maintenance.html [L] # Rewrite index to check for static RewriteRule ^/$ /index.html [QSA] # Rewrite to check for Rails cached page RewriteRule ^([^.]+)$ $1.html [QSA] # Redirect all non-static requests to cluster RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f RewriteRule ^/(.*)$ balancer://mongrel_cluster%{REQUEST_URI} [P,QSA,L] # Deflate AddOutputFilterByType DEFLATE text/html text/plain text/xml application/xml application/xhtml+xml text/javascript text/css BrowserMatch ^Mozilla/4 gzip-only-text/html BrowserMatch ^Mozilla/4\.0[678] no-gzip BrowserMatch \\bMSIE !no-gzip !gzip-only-text/html # Uncomment for deflate debugging #DeflateFilterNote Input input_info #DeflateFilterNote Output output_info #DeflateFilterNote Ratio ratio_info #LogFormat '"%r" %{output_info}n/%{input_info}n (%{ratio_info}n%%)' deflate #CustomLog logs/myapp_deflate_log deflate </VirtualHost> # httpd [example.org] dmn entry END. Does anyone know what could be wrong with it?

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• Can this be improved? Scrubbing of dangerous html tags.

  - by chobo2

  I been finding that for something that I consider pretty import there is very little information or libraries on how to deal with this problem. I found this while searching. I really don't know all the million ways that a hacker could try to insert the dangerous tags. I have a rich html editor so I need to keep non dangerous tags but strip out bad ones. So is this script missing anything? It uses html agility pack. public string ScrubHTML(string html) { HtmlDocument doc = new HtmlDocument(); doc.LoadHtml(html); //Remove potentially harmful elements HtmlNodeCollection nc = doc.DocumentNode.SelectNodes("//script|//link|//iframe|//frameset|//frame|//applet|//object|//embed"); if (nc != null) { foreach (HtmlNode node in nc) { node.ParentNode.RemoveChild(node, false); } } //remove hrefs to java/j/vbscript URLs nc = doc.DocumentNode.SelectNodes("//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'javascript')]|//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'jscript')]|//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'vbscript')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.SetAttributeValue("href", "#"); } } //remove img with refs to java/j/vbscript URLs nc = doc.DocumentNode.SelectNodes("//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'javascript')]|//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'jscript')]|//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'vbscript')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.SetAttributeValue("src", "#"); } } //remove on<Event> handlers from all tags nc = doc.DocumentNode.SelectNodes("//*[@onclick or @onmouseover or @onfocus or @onblur or @onmouseout or @ondoubleclick or @onload or @onunload]"); if (nc != null) { foreach (HtmlNode node in nc) { node.Attributes.Remove("onFocus"); node.Attributes.Remove("onBlur"); node.Attributes.Remove("onClick"); node.Attributes.Remove("onMouseOver"); node.Attributes.Remove("onMouseOut"); node.Attributes.Remove("onDoubleClick"); node.Attributes.Remove("onLoad"); node.Attributes.Remove("onUnload"); } } // remove any style attributes that contain the word expression (IE evaluates this as script) nc = doc.DocumentNode.SelectNodes("//*[contains(translate(@style, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'expression')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.Attributes.Remove("stYle"); } } return doc.DocumentNode.WriteTo(); } Edit 2 people have suggested whitelisting. I actually like the idea of whitelisting but never actually did it because no one can actually tell me how to do it in C# and I can't even really find tutorials for how to do it in c#(the last time I looked. I will check it out again). How do you make a white list? Is it just a list collection? How do you actual parse out all html tags, script tags and every other tag? Once you have the tags how do you determine which ones are allowed? Compare them to you list collection? But what happens if the content is coming in and has like 100 tags and you have 50 allowed. You got to compare each of those 100 tag by 50 allowed tags. Thats quite a bit to go through and could be slow. Once you found a invalid tag how do you remove it? I don't really want to reject a whole set of text if one tag was found to be invalid. I rather remove and insert the rest. Should I be using html agility pack?

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• What are good CLI tools for JSON?

  - by jasonmp85

  General Problem Though I may be diagnosing the root cause of an event, determining how many users it affected, or distilling timing logs in order to assess the performance and throughput impact of a recent code change, my tools stay the same: grep, awk, sed, tr, uniq, sort, zcat, tail, head, join, and split. To glue them all together, Unix gives us pipes, and for fancier filtering we have xargs. If these fail me, there's always perl -e. These tools are perfect for processing CSV files, tab-delimited files, log files with a predictable line format, or files with comma-separated key-value pairs. In other words, files where each line has next to no context. XML Analogues I recently needed to trawl through Gigabytes of XML to build a histogram of usage by user. This was easy enough with the tools I had, but for more complicated queries the normal approaches break down. Say I have files with items like this: <foo user="me"> <baz key="zoidberg" value="squid" /> <baz key="leela" value="cyclops" /> <baz key="fry" value="rube" /> </foo> And let's say I want to produce a mapping from user to average number of <baz>s per <foo>. Processing line-by-line is no longer an option: I need to know which user's <foo> I'm currently inspecting so I know whose average to update. Any sort of Unix one liner that accomplishes this task is likely to be inscrutable. Fortunately in XML-land, we have wonderful technologies like XPath, XQuery, and XSLT to help us. Previously, I had gotten accustomed to using the wonderful XML::XPath Perl module to accomplish queries like the one above, but after finding a TextMate Plugin that could run an XPath expression against my current window, I stopped writing one-off Perl scripts to query XML. And I just found out about XMLStarlet which is installing as I type this and which I look forward to using in the future. JSON Solutions? So this leads me to my question: are there any tools like this for JSON? It's only a matter of time before some investigation task requires me to do similar queries on JSON files, and without tools like XPath and XSLT, such a task will be a lot harder. If I had a bunch of JSON that looked like this: { "firstName": "Bender", "lastName": "Robot", "age": 200, "address": { "streetAddress": "123", "city": "New York", "state": "NY", "postalCode": "1729" }, "phoneNumber": [ { "type": "home", "number": "666 555-1234" }, { "type": "fax", "number": "666 555-4567" } ] } And wanted to find the average number of phone numbers each person had, I could do something like this with XPath: fn:avg(/fn:count(phoneNumber)) Questions Are there any command-line tools that can "query" JSON files in this way? If you have to process a bunch of JSON files on a Unix command line, what tools do you use? Heck, is there even work being done to make a query language like this for JSON? If you do use tools like this in your day-to-day work, what do you like/dislike about them? Are there any gotchas? I'm noticing more and more data serialization is being done using JSON, so processing tools like this will be crucial when analyzing large data dumps in the future. Language libraries for JSON are very strong and it's easy enough to write scripts to do this sort of processing, but to really let people play around with the data shell tools are needed. Related Questions Grep and Sed Equivalent for XML Command Line Processing Is there a query language for JSON? JSONPath or other XPath like utility for JSON/Javascript; or Jquery JSON

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• How do I use constructor dependency injection to supply Models from a collection to their ViewModels

  - by GraemeF

  I'm using constructor dependency injection in my WPF application and I keep running into the following pattern, so would like to get other people's opinion on it and hear about alternative solutions. The goal is to wire up a hierarchy of ViewModels to a similar hierarchy of Models, so that the responsibility for presenting the information in each model lies with its own ViewModel implementation. (The pattern also crops up under other circumstances but MVVM should make for a good example.) Here's a simplified example. Given that I have a model that has a collection of further models: public interface IPerson { IEnumerable<IAddress> Addresses { get; } } public interface IAddress { } I would like to mirror this hierarchy in the ViewModels so that I can bind a ListBox (or whatever) to a collection in the Person ViewModel: public interface IPersonViewModel { ObservableCollection<IAddressViewModel> Addresses { get; } void Initialize(); } public interface IAddressViewModel { } The child ViewModel needs to present the information from the child Model, so it's injected via the constructor: public class AddressViewModel : IAddressViewModel { private readonly IAddress _address; public AddressViewModel(IAddress address) { _address = address; } } The question is, what is the best way to supply the child Model to the corresponding child ViewModel? The example is trivial, but in a typical real case the ViewModels have more dependencies - each of which has its own dependencies (and so on). I'm using Unity 1.2 (although I think the question is relevant across the other IoC containers), and I am using Caliburn's view strategies to automatically find and wire up the appropriate View to a ViewModel. Here is my current solution: The parent ViewModel needs to create a child ViewModel for each child Model, so it has a factory method added to its constructor which it uses during initialization: public class PersonViewModel : IPersonViewModel { private readonly Func<IAddress, IAddressViewModel> _addressViewModelFactory; private readonly IPerson _person; public PersonViewModel(IPerson person, Func<IAddress, IAddressViewModel> addressViewModelFactory) { _addressViewModelFactory = addressViewModelFactory; _person = person; Addresses = new ObservableCollection<IAddressViewModel>(); } public ObservableCollection<IAddressViewModel> Addresses { get; private set; } public void Initialize() { foreach (IAddress address in _person.Addresses) Addresses.Add(_addressViewModelFactory(address)); } } A factory method that satisfies the Func<IAddress, IAddressViewModel> interface is registered with the main UnityContainer. The factory method uses a child container to register the IAddress dependency that is required by the ViewModel and then resolves the child ViewModel: public class Factory { private readonly IUnityContainer _container; public Factory(IUnityContainer container) { _container = container; } public void RegisterStuff() { _container.RegisterInstance<Func<IAddress, IAddressViewModel>>(CreateAddressViewModel); } private IAddressViewModel CreateAddressViewModel(IAddress model) { IUnityContainer childContainer = _container.CreateChildContainer(); childContainer.RegisterInstance(model); return childContainer.Resolve<IAddressViewModel>(); } } Now, when the PersonViewModel is initialized, it loops through each Address in the Model and calls CreateAddressViewModel() (which was injected via the Func<IAddress, IAddressViewModel> argument). CreateAddressViewModel() creates a temporary child container and registers the IAddress model so that when it resolves the IAddressViewModel from the child container the AddressViewModel gets the correct instance injected via its constructor. This seems to be a good solution to me as the dependencies of the ViewModels are very clear and they are easily testable and unaware of the IoC container. On the other hand, performance is OK but not great as a lot of temporary child containers can be created. Also I end up with a lot of very similar factory methods. Is this the best way to inject the child Models into the child ViewModels with Unity? Is there a better (or faster) way to do it in other IoC containers, e.g. Autofac? How would this problem be tackled with MEF, given that it is not a traditional IoC container but is still used to compose objects?

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• How do I get through proxy server environments for non-standard services?

  - by Ripred

  I'm not real hip on exactly what role(s) today's proxy servers can play and I'm learning so go easy on me :-) I have a client/server system I have written using a homegrown protocol and need to enhance the client side to negotiate its way out of a proxy environment. I have an existing client and server system written in C and C++ for the speed and a small amount of MFC in the client to handle the user interface. I have written both the server and client side of the system on Windows (the people I work for are mainly web developers using Windows everything - not a choice) sticking to Berkeley Sockets as it were via wsock32 for efficiency. The clients connect to the server through a nonstandard port (even though using port 80 is an option to get out of some environments but the protocol that goes over it isn't HTTP). The TCP connection(s) stay open for the duration of the clients participation in real time conferences. Our customer base is expanding to all kinds of networked environments. I have been able to solve a lot of problems by adding the ability to connect securely over port 443 and using secure sockets which allows the protocol to pass through a lot environments since the internal packets can't be sniffed. But more and more of our customers are behind a proxy server environment and my direct connections don't make it through. My old school understanding of proxy servers is that they act as a proxy for external HTML content over HTTP, possibly locally caching popular material for faster local access, and also allowing their IT staff to blacklist certain destination sites. Customer are complaining that my software doesn't recognize and easily navigate its way through their proxy environments but I'm finding it difficult to decide what my "best fit" solution should be. My software doesn't tear down the connection after each client request, and on top of that packets can come from either side at any time, basically your typical custom client/server system for a specific niche. My first reaction is "why can't they just add my servers addresses to their white list" but if there is a programmatic way I can get through without requiring their IT staff to help it is politically better and arguably a better solution anyway. Plus maybe I'm still not understanding the role and purpose of what proxy servers and environments have grown to be these days. My first attempt at a solution was to use WinInet with its various proxy capabilities to establish a connection over port 80 to my non-standard protocol server (which knows enough to recognize and answer a simple HTTP-looking GET request and answer it with a simple HTTP response page to get around some environments that employ initial packet sniffing (DPI)). I retrieved the actual SOCKET handle behind WinInet's HINTERNET request object and had hoped to use that in place of my software's existing SOCKET connection and hopefully not need to change much more on the client side. It initially seemed to be my solution but on further inspection it seems that the OS gets first-chance at the received data on this socket since when I get notified of events via the standard select(...) statement on the socket and query the size of the data available via ioctlsocket the call succeeds but returns 0 bytes available, the reads don't work and it goes downhill from there. Can someone tell me of a client-side library (commercial is fine) will let me get past these proxy server environments with as little user and IT staff help as possible? From what I read it has grown past SOCKS and I figure someone has to have solved this problem before me. Thanks for reading my long-winded question, Ripred

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• com.sun.org.apache.xerces.internal.dom.DocumentImpl cannot be cast to org.codehaus.plexus.util.xml.X

  - by Random

  Afetr using the Model library (see this) for my Maven pom.xml during this weeks I jumped on this error while attempting to write a ConfiguratonContainer into the pom.xml. The javadoc for Model says: public void setConfiguration(Object configuration) Set the configuration as DOM object. Parameters: configuration - So I made some xml with Document (org.w3c.dom.Document) and the xml parser standar javax library. You know the code (it's through all the net) but I paste it here... DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder parser = factory.newDocumentBuilder(); Document doc =parser.newDocument(); And then you fill the code with Element declaration,a lot of appendChild and such. And tried to make it work. Doesn't seem to do well. First tried using plugin.setConfiguration(doc); But it didn't work. Then I tried Obejct obj = doc; plugin.setConfiguration(obj); But it didn't work. Then I searched the net for answers, and guess... It didn't work. There are like 0 people using this library (maven.model) in all the net. So here am I again, asking the senseis for help. Where is my error? I have downloaded the source code of the library trying to see where is the error, but it seems to be ok (as should). I add the stackrace for reference java.lang.ClassCastException: com.sun.org.apache.xerces.internal.dom.DocumentImpl cannot be cast to org.codehaus.plexus.util.xml.Xpp3Dom at org.apache.maven.model.io.xpp3.MavenXpp3Writer.writePlugin(MavenXpp3Writer.java:1472) at org.apache.maven.model.io.xpp3.MavenXpp3Writer.writeBuild(MavenXpp3Writer.java:326) at org.apache.maven.model.io.xpp3.MavenXpp3Writer.writeModel(MavenXpp3Writer.java:1093) at org.apache.maven.model.io.xpp3.MavenXpp3Writer.write(MavenXpp3Writer.java:102) at com.mapfre.mutua.PDA.model.GeneratePOM.createPOM(GeneratePOM.java:28) at com.mapfre.mutua.PDA.prueba.MavenPOM.generatePOMWAR(MavenPOM.java:681) at com.mapfre.mutua.PDA.prueba.GenerarPOMMapfreAction.execute(GenerarPOMMapfreAction.java:36) at org.apache.struts.chain.commands.servlet.ExecuteAction.execute(ExecuteAction.java:58) at org.apache.struts.chain.commands.AbstractExecuteAction.execute(AbstractExecuteAction.java:67) at org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51) at org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:191) at org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:305) at org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:191) at org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283) at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913) at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462) at javax.servlet.http.HttpServlet.service(HttpServlet.java:647) at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:873) at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665) at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528) at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689) at java.lang.Thread.run(Unknown Source)

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• easiest and best way to make a server queue java

  - by houlahan

  i have a server at the moment which makes a new thread for every user connected but after about 6 people are on the server for more than 15 mins it tends to flop and give me java heap out of memory error i have 1 thread that checks with a mysql database every 30 seconds to see if any of the users currently logged on have any new messages. what would be the easiest way to implement a server queue? this is the my main method for my server: public class Server { public static int MaxUsers = 1000; //public static PrintStream[] sessions = new PrintStream[MaxUsers]; public static ObjectOutputStream[] sessions = new ObjectOutputStream[MaxUsers]; public static ObjectInputStream[] ois = new ObjectInputStream[MaxUsers]; private static int port = 6283; public static Connection conn; static Toolkit toolkit; static Timer timer; public static void main(String[] args) { try { conn = (Connection) Mysql.getConnection(); } catch (Exception ex) { Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex); } System.out.println("****************************************************"); System.out.println("* *"); System.out.println("* Cloud Server *"); System.out.println("* ©2010 *"); System.out.println("* *"); System.out.println("* Luke Houlahan *"); System.out.println("* *"); System.out.println("* Server Online *"); System.out.println("* Listening On Port " + port + " *"); System.out.println("* *"); System.out.println("****************************************************"); System.out.println(""); mailChecker(); try { int i; ServerSocket s = new ServerSocket(port); for (i = 0; i < MaxUsers; ++i) { sessions[i] = null; } while (true) { try { Socket incoming = s.accept(); boolean found = false; int numusers = 0; int usernum = -1; synchronized (sessions) { for (i = 0; i < MaxUsers; ++i) { if (sessions[i] == null) { if (!found) { sessions[i] = new ObjectOutputStream(incoming.getOutputStream()); ois[i]= new ObjectInputStream(incoming.getInputStream()); new SocketHandler(incoming, i).start(); found = true; usernum = i; } } else { numusers++; } } if (!found) { ObjectOutputStream temp = new ObjectOutputStream(incoming.getOutputStream()); Person tempperson = new Person(); tempperson.setFlagField(100); temp.writeObject(tempperson); temp.flush(); temp = null; tempperson = null; incoming.close(); } else { } } } catch (IOException ex) { System.out.println(1); Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex); } } } catch (IOException ex) { System.out.println(2); Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex); } } public static void mailChecker() { toolkit = Toolkit.getDefaultToolkit(); timer = new Timer(); timer.schedule(new mailCheck(), 0, 10 * 1000); } }

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• Unnecessary Java context switches

  - by Paul Morrison

  I have a network of Java Threads (Flow-Based Programming) communicating via fixed-capacity channels - running under WindowsXP. What we expected, based on our experience with "green" threads (non-preemptive), would be that threads would switch context less often (thus reducing CPU time) if the channels were made bigger. However, we found that increasing channel size does not make any difference to the run time. What seems to be happening is that Java decides to switch threads even though channels aren't full or empty (i.e. even though a thread doesn't have to suspend), which costs CPU time for no apparent advantage. Also changing Thread priorities doesn't make any observable difference. My question is whether there is some way of persuading Java not to make unnecessary context switches, but hold off switching until it is really necessary to switch threads - is there some way of changing Java's dispatching logic? Or is it reacting to something I didn't pay attention to?! Or are there other asynchronism mechanisms, e.g. Thread factories, Runnable(s), maybe even daemons (!). The answer appears to be non-obvious, as so far none of my correspondents has come up with an answer (including most recently two CS profs). Or maybe I'm missing something that's so obvious that people can't imagine my not knowing it... I've added the send and receive code here - not very elegant, but it seems to work...;-) In case you are wondering, I thought the goLock logic in 'send' might be causing the problem, but removing it temporarily didn't make any difference. I have added the code for send and receive... public synchronized Packet receive() { if (isDrained()) { return null; } while (isEmpty()) { try { wait(); } catch (InterruptedException e) { close(); return null; } if (isDrained()) { return null; } } if (isDrained()) { return null; } if (isFull()) { notifyAll(); // notify other components waiting to send } Packet packet = array[receivePtr]; array[receivePtr] = null; receivePtr = (receivePtr + 1) % array.length; //notifyAll(); // only needed if it was full usedSlots--; packet.setOwner(receiver); if (null == packet.getContent()) { traceFuncs("Received null packet"); } else { traceFuncs("Received: " + packet.toString()); } return packet; } synchronized boolean send(final Packet packet, final OutputPort op) { sender = op.sender; if (isClosed()) { return false; } while (isFull()) { try { wait(); } catch (InterruptedException e) { indicateOneSenderClosed(); return false; } sender = op.sender; } if (isClosed()) { return false; } try { receiver.goLock.lockInterruptibly(); } catch (InterruptedException ex) { return false; } try { packet.clearOwner(); array[sendPtr] = packet; sendPtr = (sendPtr + 1) % array.length; usedSlots++; // move this to here if (receiver.getStatus() == StatusValues.DORMANT || receiver.getStatus() == StatusValues.NOT_STARTED) { receiver.activate(); // start or wake up if necessary } else { notifyAll(); // notify receiver // other components waiting to send to this connection may also get // notified, // but this is handled by while statement } sender = null; Component.network.active = true; } finally { receiver.goLock.unlock(); } return true; }

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• How to design a C / C++ library to be usable in many client languages?

  - by Brian Schimmel

  I'm planning to code a library that should be usable by a large number of people in on a wide spectrum of platforms. What do I have to consider to design it right? To make this questions more specific, there are four "subquestions" at the end. Choice of language Considering all the known requirements and details, I concluded that a library written in C or C++ was the way to go. I think the primary usage of my library will be in programs written in C, C++ and Java SE, but I can also think of reasons to use it from Java ME, PHP, .NET, Objective C, Python, Ruby, bash scrips, etc... Maybe I cannot target all of them, but if it's possible, I'll do it. Requirements It would be to much to describe the full purpose of my library here, but there are some aspects that might be important to this question: The library itself will start out small, but definitely will grow to enormous complexity, so it is not an option to maintain several versions in parallel. Most of the complexity will be hidden inside the library, though The library will construct an object graph that is used heavily inside. Some clients of the library will only be interested in specific attributes of specific objects, while other clients must traverse the object graph in some way Clients may change the objects, and the library must be notified thereof The library may change the objects, and the client must be notified thereof, if it already has a handle to that object The library must be multi-threaded, because it will maintain network connections to several other hosts While some requests to the library may be handled synchronously, many of them will take too long and must be processed in the background, and notify the client on success (or failure) Of course, answers are welcome no matter if they address my specific requirements, or if they answer the question in a general way that matters to a wider audience! My assumptions, so far So here are some of my assumptions and conclusions, which I gathered in the past months: Internally I can use whatever I want, e.g. C++ with operator overloading, multiple inheritance, template meta programming... as long as there is a portable compiler which handles it (think of gcc / g++) But my interface has to be a clean C interface that does not involve name mangling Also, I think my interface should only consist of functions, with basic/primitive data types (and maybe pointers) passed as parameters and return values If I use pointers, I think I should only use them to pass them back to the library, not to operate directly on the referenced memory For usage in a C++ application, I might also offer an object oriented interface (Which is also prone to name mangling, so the App must either use the same compiler, or include the library in source form) Is this also true for usage in C# ? For usage in Java SE / Java EE, the Java native interface (JNI) applies. I have some basic knowledge about it, but I should definitely double check it. Not all client languages handle multithreading well, so there should be a single thread talking to the client For usage on Java ME, there is no such thing as JNI, but I might go with Nested VM For usage in Bash scripts, there must be an executable with a command line interface For the other client languages, I have no idea For most client languages, it would be nice to have kind of an adapter interface written in that language. I think there are tools to automatically generate this for Java and some others For object oriented languages, it might be possible to create an object oriented adapter which hides the fact that the interface to the library is function based - but I don't know if its worth the effort Possible subquestions is this possible with manageable effort, or is it just too much portability? are there any good books / websites about this kind of design criteria? are any of my assumptions wrong? which open source libraries are worth studying to learn from their design / interface / souce? meta: This question is rather long, do you see any way to split it into several smaller ones? (If you reply to this, do it as a comment, not as an answer)

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• Isn't it better to use a single try catch instead of tons of TryParsing and other error handling sometimes?

  - by Ryan Peschel

  I know people say it's bad to use exceptions for flow control and to only use exceptions for exceptional situations, but sometimes isn't it just cleaner and more elegant to wrap the entire block in a try-catch? For example, let's say I have a dialog window with a TextBox where the user can type input in to be parsed in a key-value sort of manner. This situation is not as contrived as you might think because I've inherited code that has to handle this exact situation (albeit not with farm animals). Consider this wall of code: class Animals { public int catA, catB; public float dogA, dogB; public int mouseA, mouseB, mouseC; public double cow; } class Program { static void Main(string[] args) { string input = "Sets all the farm animals CAT 3 5 DOG 21.3 5.23 MOUSE 1 0 1 COW 12.25"; string[] splitInput = input.Split(' '); string[] animals = { "CAT", "DOG", "MOUSE", "COW", "CHICKEN", "GOOSE", "HEN", "BUNNY" }; Animals animal = new Animals(); for (int i = 0; i < splitInput.Length; i++) { string token = splitInput[i]; if (animals.Contains(token)) { switch (token) { case "CAT": animal.catA = int.Parse(splitInput[i + 1]); animal.catB = int.Parse(splitInput[i + 2]); break; case "DOG": animal.dogA = float.Parse(splitInput[i + 1]); animal.dogB = float.Parse(splitInput[i + 2]); break; case "MOUSE": animal.mouseA = int.Parse(splitInput[i + 1]); animal.mouseB = int.Parse(splitInput[i + 2]); animal.mouseC = int.Parse(splitInput[i + 3]); break; case "COW": animal.cow = double.Parse(splitInput[i + 1]); break; } } } } } In actuality there are a lot more farm animals and more handling than that. A lot of things can go wrong though. The user could enter in the wrong number of parameters. The user can enter the input in an incorrect format. The user could specify numbers too large or too small for the data type to handle. All these different errors could be handled without exceptions through the use of TryParse, checking how many parameters the user tried to use for a specific animal, checking if the parameter is too large or too small for the data type (because TryParse just returns 0), but every one should result in the same thing: A MessageBox appearing telling the user that the inputted data is invalid and to fix it. My boss doesn't want different message boxes for different errors. So instead of doing all that, why not just wrap the block in a try-catch and in the catch statement just display that error message box and let the user try again? Maybe this isn't the best example but think of any other scenario where there would otherwise be tons of error handling that could be substituted for a single try-catch. Is that not the better solution?

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