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• Strategy for locale sensitive sort with pagination

  - by Thom Birkeland

  Hi, I work on an application that is deployed on the web. Part of the app is search functions where the result is presented in a sorted list. The application targets users in several countries using different locales (= sorting rules). I need to find a solution for sorting correctly for all users. I currently sort with ORDER BY in my SQL query, so the sorting is done according to the locale (or LC_LOCATE) set for the database. These rules are incorrect for those users with a locale different than the one set for the database. Also, to further complicate the issue, I use pagination in the application, so when I query the database I ask for rows 1 - 15, 16 - 30, etc. depending on the page I need. However, since the sorting is wrong, each page contains entries that are incorrectly sorted. In a worst case scenario, the entire result set for a given page could be out of order, depending on the locale/sorting rules of the current user. If I were to sort in (server side) code, I need to retrieve all rows from the database and then sort. This results in a tremendous performance hit given the amount of data. Thus I would like to avoid this. Does anyone have a strategy (or even technical solution) for attacking this problem that will result in correctly sorted lists without having to take the performance hit of loading all data? Tech details: The database is PostgreSQL 8.3, the application an EJB3 app using EJB QL for data query, running on JBoss 4.5.

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• Game engine deployment strategy for the Android?

  - by Jeremy Bell

  In college, my senior project was to create a simple 2D game engine complete with a scripting language which compiled to bytecode, which was interpreted. For fun, I'd like to port the engine to android. I'm new to android development, so I'm not sure which way to go as far as deploying the engine on the phone. The easiest way I suppose would be to require the engine/interpreter to be bundled with every game that uses it. This solves any versioning issues. There are two problems with this. One: this makes each game app larger and two: I originally released the engine under the LGPL license (unfortunately), but this deployment strategy makes it difficult to conform to the rules of that license, particularly with respect to allowing users to replace the lib easily with another version. So, my other option is to somehow have the engine stand alone as an Activity or service that somehow responds to intents raised by game apps, and somehow give the engine app permissions to read the scripts and other assets to "run" the game. The user could then be able to replace the engine app with a different version (possibly one they made themselves). Is this even possible? What would you recommend? How could I handle it in a secure way?

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• Connection Pool Strategy: Good, Bad or Ugly?

  - by Drew

  I'm in charge of developing and maintaining a group of Web Applications that are centered around similar data. The architecture I decided on at the time was that each application would have their own database and web-root application. Each application maintains a connection pool to its own database and a central database for shared data (logins, etc.) A co-worker has been positing that this strategy will not scale because having so many different connection pools will not be scalable and that we should refactor the database so that all of the different applications use a single central database and that any modifications that may be unique to a system will need to be reflected from that one database and then use a single pool powered by Tomcat. He has posited that there is a lot of "meta data" that goes back and forth across the network to maintain a connection pool. My understanding is that with proper tuning to use only as many connections as necessary across the different pools (low volume apps getting less connections, high volume apps getting more, etc.) that the number of pools doesn't matter compared to the number of connections or more formally that the difference in overhead required to maintain 3 pools of 10 connections is negligible compared to 1 pool of 30 connections. The reasoning behind initially breaking the systems into a one-app-one-database design was that there are likely going to be differences between the apps and that each system could make modifications on the schema as needed. Similarly, it eliminated the possibility of system data bleeding through to other apps. Unfortunately there is not strong leadership in the company to make a hard decision. Although my co-worker is backing up his worries only with vagueness, I want to make sure I understand the ramifications of multiple small databases/connections versus one large database/connection pool.

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• Resource placement (optimal strategy)

  - by blackened

  I know that this is not exactly the right place to ask this question, but maybe a wise guy comes across and has the solution. I'm trying to write a computer game and I need an algorithm to solve this question: The game is played between 2 players. Each side has 1.000 dollars. There are three "boxes" and each player writes down the amount of money he is going to place into those boxes. Then these amounts are compared. Whoever placed more money in a box scores 1 point (if draw half point each). Whoever scores more points wins his opponents 1.000 dollars. Example game: Player A: [500, 500, 0] Player B: [333, 333, 334] Player A wins because he won Box A and Box B (but lost Box C). Question: What is the optimal strategy to place the money? I have more questions to ask (algorithm related, not math related) but I need to know the answer to this one first. Update (1): After some more research I've learned that these type of problems/games are called Colonel Blotto Games. I did my best and found few (highly technical) documents on the subject. Cutting it short, the problem I have (as described above) is called simple Blotto Game (only three battlefields with symmetric resources). The difficult ones are the ones with, say, 10+ battle fields with non-symmetric resources. All the documents I've read say that the simple Blotto game is easy to solve. The thing is, none of them actually say what that "easy" solution is.

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• Which design pattern fits - strategy makes sense ?

  - by user554833

  --Bump *One desperate try to get someone's attention I have a simple database table that stores list of users who have subscribed to folders either by email OR to show up on the site (only on the web UI). In the storage table this is controlled by a number(1 - show on site 2- by email). When I am showing in UI I need to show a checkbox next to each of folders for which the user has subscribed (both email & on site). There is a separate table which stores a set of default subscriptions which would apply to each user if user has not expressed his subscription. This is basically a folder ID and a virtual group name. But, Email subscriptions do not count for applying these default groups. So if no "on site" subscription apply default group. Thats the rule. How about a strategy pattern here (Pseudo code) Interface ISubscription public ArrayList GetSubscriptionData(Pass query object) Public class SubscriptionWithDefaultGroup Implement ArrayList GetSubscriptionData(Pass query object) Public class SubscriptionWithoutDefaultGroup Implement ArrayList GetSubscriptionData(Pass query object) Public class SubscriptionOnlyDefaultGroup Implement ArrayList GetSubscriptionData(Pass query object) does this even make sense? I would be more than glad for receive any criticism / help / notes. I am learning. Cheers

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• App hosting Report Viewer crashes on exit after export

  - by Paul Sasik

  We have a .NET Winforms application that hosts the Crystal Reports Viewer control (Version XI). It works well for the most part but when an export of data from the viewer is performed the application will crash on exit and in unmanaged code. The error message is not very useful and just says that an incorrect memory location was accessed. No other info such a specific DLL etc. is provided. This only happens after the viewer is used to export a report to CSV, XML etc. My guess is that at some point in the export process Crystal creates a resource that attempts an action on shut down to a parent window (perhaps) that no longer exists. I've seen a number of memory leak and shut down issues with Crystal but this one's new. Has anyone seen it and come up with a workaround or has ideas for workarounds? So far we've tried explicitly disposing of all crystal-related objects, setting to null and even setting a Thread.Sleep cycle on shut down to "give Crystal time to clean up." Update: The crash happens only on shut down (so not immediate) All export formats work All export files are created properly CR is installed on the same machine as the hosting .NET app not sure about exporting from the IDE... is that even possible?

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• how to let the parser print help message rather than error and exit

  - by fluter

  Hi, I am using argparse to handle cmd args, I wanna if there is no args specified, then print the help message, but now the parse will output a error, and then exit. my code is: def main(): print "in abing/start/main" parser = argparse.ArgumentParser(prog="abing")#, usage="%(prog)s <command> [args] [--help]") parser.add_argument("-v", "--verbose", action="store_true", default=False, help="show verbose output") subparsers = parser.add_subparsers(title="commands") bkr_subparser = subparsers.add_parser("beaker", help="beaker inspection") bkr_subparser.set_defaults(command=beaker_command) bkr_subparser.add_argument("-m", "--max", action="store", default=3, type=int, help="max resubmit count") bkr_subparser.add_argument("-g", "--grain", action="store", default="J", choices=["J", "RS", "R", "T", "job", "recipeset", "recipe", "task"], type=str, help="resubmit selection granularity") bkr_subparser.add_argument("job_ids", nargs=1, action="store", help="list of job id to be monitored") et_subparser = subparsers.add_parser("errata", help="errata inspection") et_subparser.set_defaults(command=errata_command) et_subparser.add_argument("-w", "--workflows", action="store_true", help="generate workflows for the erratum") et_subparser.add_argument("-r", "--run", action="store_true", help="generate workflows, and run for the erratum") et_subparser.add_argument("-s", "--start-monitor", action="store_true", help="start monitor the errata system") et_subparser.add_argument("-d", "--daemon", action="store_true", help="run monitor into daemon mode") et_subparser.add_argument("erratum", action="store", nargs=1, metavar="ERRATUM", help="erratum id") if len(sys.argv) == 1: parser.print_help() return args = parser.parse_args() args.command(args) return how can I do that? thanks.

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• Make a PHP GET request from a PHP script and exit

  - by Abs

  Hello all, Is there something simpler than the following. I am trying to make a GET request to a PHP script and then exit the current script. I think this is a job for CURL but is there something simpler as I don't want to really worry about enabling the CURL php extension? In addition, will the below start the PHP script and then just come back and not wait for it to finish? //set GET variables $url = 'http://domain.com/get-post.php'; $fields = array( 'lname'=>urlencode($last_name), 'fname'=>urlencode($first_name) ); //url-ify the data for the GET foreach($fields as $key=>$value) { $fields_string .= $key.'='.$value.'&'; } rtrim($fields_string,'&'); //open connection $ch = curl_init(); //set the url, number of POST vars, POST data curl_setopt($ch,CURLOPT_URL,$url); curl_setopt($ch,CURLOPT_GET,count($fields)); curl_setopt($ch,CURLOPT_GETFIELDS,$fields_string); //execute GET $result = curl_exec($ch); //close connection curl_close($ch); I want to run the other script which contains functions when a condition is met so a simple include won't work as the if condition wraps around the functions, right? Please note, I am on windows machine and the code I am writing will only be used on a Windows OS. Thanks all for any help and advice

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• Rails exit controller after rendering

  - by codysehl

  I have an action in my controller that I am having trouble with. This is my first rails app, so I'm not sure of the best practices surrounding rails. I have a model called Group and a few actions that go in it's controller. I have written a test that should cause the controller to render an error in JSON because of an invalid Group ID. Instead of rendering and exiting, it looks like the controller is rendering and continuing to execute. Test test 'should not remove group because of invalid group id' do post(:remove, {'group_id' => '3333'}) response = JSON.parse(@response.body) assert_response :success assert_equal 'Success', response['message'] end Controller action # Post remove # group_id def remove if((@group = Group.find_by_id(params[:group_id])) == nil) render :json => { :message => "group_id not found" } end @group.destroy if(!Group.exists?(@group)) render :json => { :message => "Success" } else render :json => { :errors => @group.errors.full_messages } end end In the controller, the first if statement executes: render :json => { :message => "group_id not found" } but @group.destroy is still being executed. This seems counter-intuitive to me, I would think that the render method should exit the controller. Why is the controller not exiting after render is called? The purpose of this block of code is to recover gracefully when no record can be found with the passed in ID. Is this the correct way of doing something like this?

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• What is "Call By Name"?

  - by forellana

  Hi to everyone! I'm working in a homework, and the professor asked me to implement the evaluation strategy called "call by name" in scheme in a certain language that we developed and he gave us an example at http://www.scala-lang.org/node/138 in the scala language, but i don't understand in what consists the call by name evaluation strategy? what differences it has with call by need? thanks, greetings

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• How to auto advance a PowerPoint slide after an exit animation is over?

  - by joooc

  PowerPoint entrance animation set up with "Start: With Previous" starts right when a new slide is advanced. However, if you set up an exit animation in the same way, it doesn't start with a slide ending sequence. Instead, the "Start: On Click" trigger needs to be used and after your exit animation is over you still need one extra click just to advance to the next slide. Workarounds to this are obvious: create a duplicate slide, make your ending animations from the original slide being your starting animations on the duplicate slide and let them be followed with whatever you want or create a transition slide with those ending animations only and set up "Change Advance slide - Automatically after - [the time it takes your animations to finish]". These workarounds will make it work for your audience, visually. However, it has an impact on slide numbers you might need to adjust accordingly and/or duplicate content changes. If you are the only one creating and using your presentation, this might be just fine. But if you are creating a presentation in collaborative mode with three other people and don't even know who will be the presenter at the end, you can mess things up. Let's be specific: most of my slides have 0.2s fly in entrance animation applied to blocks of content coming from right, bottom or left. Advancing to the next slide I want them to fly out in another 0.2s exit animation being followed by new slide 0.2s fly in entrance animation of the new blocks. The swapping of the blocks should be triggered while advancing to the next slide, as usually. As mentioned, I'm not able to achieve this without one extra click between the slides. I wrote a VBA script that should start together with an exit animation and will auto advance a slide after 0.3s when the exit animation is over. That way I should get rid of those extra clicks which are needed right now. Sub nextslide() iTime = 0.3 Start = Timer While Timer < Start + iTime DoEvents Wend With SlideShowWindows(1).View .GotoSlide (ActivePresentation.SlideShowWindow.View.Slide.SlideIndex + 1) End With End Sub It works well when binded on a box, button or another object. But I can't make it run on a single click (anywhere on the slide) so that it could start together with the exit animation onclick trigger. Creating a big transparent rectangular shape over the whole slide and binding the macro on it doesn't help either. By clicking it you only get the macro running, exit animation is not triggered. Anyway, I don't want to bind the macro to any other workaround object but the slide itself. Anyone knows how to trigger a PowerPoint VBA script on slide onclick event? Anyone knows a secret setting that will make the exit animation work as expected i.e. animating right before exiting a slide while transitioning to the next one? Anyone knows how to beat this dragon? Thank you!

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• undefined reference to `main' collect2: ld returned 1 exit status

  - by sobingt

  I am working on this QT project and i am making test cases for my project. Here is a small test case #include <QApplication> #include <QPalette> #include <QPixmap> #include <QSplashScreen> #include <qthread.h> #define BOOST_TEST_MAIN #include <boost/test/unit_test.hpp> #include <boost/make_shared.hpp> # include <boost/thread.hpp> #include "MainWindow.h" namespace { const std::string dbname = "Project.db"; struct SongFixture { SongFixture(const std::string &fixturePath) { // Create the Master file Master::creator(); // Create/open file std::pair<int, SQLiteDbPtr> result = open( dbname, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, 0); if (result.first != SQLITE_OK) { throw SQLiteError(result.first, sqlite3_errmsg(result.second.get())); } SQLiteDbPtr &spDb = result.second; // Execute all the SQL from the fixture file execSQLFromFile(spDb, fixturePath); } }; std::auto_ptr<SongFixture> pf; } class I : public QThread { public: static void sleep(unsigned long secs) { QThread::sleep(secs); } }; void free_test_function() { BOOST_CHECK(true ); } test_suite* init_unit_test_suite(int argc, char *argv[]) { // Create a fixture for the peer: // Manage fixture creation manually instead of using // BOOST_FIXTURE_TEST_CASE because the fixture depends on runtime args. std::ostringstream fixturePathSS; fixturePathSS << PROJECT_DIR << "/test/songs_fixture.sql"; std::string fixturePath = fixturePathSS.str(); pf.reset(new SongFixture(fixturePath)); QApplication app(argc, argv); MainWindow window("artists"); window.show(); framework::master_test_suite().add( BOOST_TEST_CASE( &free_test_function )); return app.exec(); } Well i am getting any error /usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../x86_64-linux-gnu/crt1.o: In function _start': (.text+0x20): undefined reference tomain' collect2: ld returned 1 exit status pls help me you have a lead..thankz I tired adding #define BOOST_TEST_MAIN then i get ../test/UI/main.cpp: In function ‘boost::unit_test::test_suite* init_unit_test_suite(int, char**)’: ../test/UI/main.cpp:75:31: error: redefinition of ‘boost::unit_test::test_suite* init_unit_test_suite(int, char**)’ /usr/local/include/boost/test/unit_test_suite.hpp:223:1: error: ‘boost::unit_test::test_suite* init_unit_test_suite(int, char**)’ previously defined here Well the program is working in Windows but in Linux the above mention problem is observed

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• What does the status code of the Perl interpreter mean?

  - by futureelite7

  Hi, This might sound slightly confusing, but please bear with me. I'm trying to execute a copy of the Perl interpreter using Java's Runtime.exec(). However, it returned error code 9. After running the file a few times, the perl interpreter mysteriously started to return code 253 with no changes in my command at all. What does code 253 / code 9 mean? A google search for perl interpreter's exit codes turned up nothing. Where can I find a list of exit codes for the Perl interpreter? Thanks!

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• What might cause ruby to lock up while exiting?

  - by user30997

  I have a ruby script that does a few perforce operations (through the scripting API) then simply ends: def foo() ... end def bar() ... end foo() bar() puts __LINE__ exit 0 #end of file ...and while the LINE will print out, the process never ends, whether the exit(0) is there or not. This is ruby 1.8.6, primarily on the mac, but I'm seeing this on the PC as well. I'm doing the usual google poking around, but hoped there might be a voice of experience here to bank on. Thanks.

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• Exit code 3 (not my return value, looking for source)

  - by Kathoz

  Greetings, my program exits with the code 3. No error messages, no exceptions, and the exit is not initiated by my code. The problem occurs when I am trying to read extremely long integer values from a text file (the text file is present and correctly opened, with successful prior reading). I am using very large amounts of memory (in fact, I think that this might be the cause, as I am nearly sure I go over the 2GB per process memory limit). I am also using the GMP (or, rather, MPIR) library to multiply bignums. I am fairly sure that this is not a file I/O problem as I got the same error code on a previous program version that was fully in-memory. System: MS Visual Studio 2008 MS Windows Vista Home Premium x86 MPIR 2.1.0 rc2 4GB RAM Where might this error code originate from? EDIT: this is the procedure that exits with the code void condenseBinSplitFile(const char *sourceFilename, int partCount){ //condense results file into final P and Q std::string tempFilename; std::string inputFilename(sourceFilename); std::string outputFilename(BIN_SPLIT_FILENAME_DATA2); mpz_class *P = new mpz_class(0); mpz_class *Q = new mpz_class(0); mpz_class *PP = new mpz_class(0); mpz_class *QQ = new mpz_class(0); FILE *sourceFile; FILE *resultFile; fpos_t oldPos; int swapCount = 0; while (partCount > 1){ std::cout << partCount << std::endl; sourceFile = fopen(inputFilename.c_str(), "r"); resultFile = fopen(outputFilename.c_str(), "w"); for (int i=0; i<partCount/2; i++){ //Multiplication order: //Get Q, skip P //Get QQ, mul Q and QQ, print Q, delete Q //Jump back to P, get P //Mul P and QQ, delete QQ //Skip QQ, get PP //Mul P and PP, delete P and PP //Get Q, skip P mpz_inp_str(Q->get_mpz_t(), sourceFile, CALC_BASE); fgetpos(sourceFile, &oldPos); skipLine(sourceFile); skipLine(sourceFile); //Get QQ, mul Q and QQ, print Q, delete Q mpz_inp_str(QQ->get_mpz_t(), sourceFile, CALC_BASE); (*Q) *= (*QQ); mpz_out_str(resultFile, CALC_BASE, Q->get_mpz_t()); fputc('\n', resultFile); (*Q) = 0; //Jump back to P, get P fsetpos(sourceFile, &oldPos); mpz_inp_str(P->get_mpz_t(), sourceFile, CALC_BASE); //Mul P and QQ, delete QQ (*P) *= (*QQ); (*QQ) = 0; //Skip QQ, get PP skipLine(sourceFile); skipLine(sourceFile); mpz_inp_str(PP->get_mpz_t(), sourceFile, CALC_BASE); //Mul P and PP, delete PP, print P, delete P (*P) += (*PP); (*PP) = 0; mpz_out_str(resultFile, CALC_BASE, P->get_mpz_t()); fputc('\n', resultFile); (*P) = 0; } partCount /= 2; fclose(sourceFile); fclose(resultFile); //swap filenames tempFilename = inputFilename; inputFilename = outputFilename; outputFilename = tempFilename; swapCount++; } delete P; delete Q; delete PP; delete QQ; remove(BIN_SPLIT_FILENAME_RESULTS); if (swapCount%2 == 0) rename(sourceFilename, BIN_SPLIT_FILENAME_RESULTS); else rename(BIN_SPLIT_FILENAME_DATA2, BIN_SPLIT_FILENAME_RESULTS); }

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• How can I close my software in a save way?

  - by Roman

  Up to now I used my application as a stand alone product. So, when user pressed "Stop" button I called System.exit(0); and it was fine. Now my application will be called (in a programmatic way) from another program. So, I afraid that System.exit(0); will kill not only my process but also the external software which started my program. So, what is the correct way to shutdown my application if a corresponding request from an external software is received? My application is an GUI application. So, I want to close the window but I also want to close all processes performed by my program. ADDED: To be more specific, I want to close all threads started by my program. My program does not start any OS process or any other program.

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• Detecting when a process has finished (but not exited)

  - by Egwor

  I have a program that's run in unix (that I have no control over) that when finished prints 'Completed successfully' but does not exit. I want to automatically detect when the process finishes (by checking the output of the command), so that I can kill the process and so that I can proceed do other activities. The complexity comes because I want to be able to run multiples of these scripts concurrently. (One activity I need to do requires the script to be called with various inputs, but each time the script runs it takes a while to return, and so I want to do them in parallel) Has anyone done something similar to this? I could redirect the stderr and stdout output of the command to a temporary file which has a random file name, then tail the file and pipe to grep for the end conditions (I.e. the certain log lines). The problem is, surely tail -f would keep running, and so it would never exit. Should I poll? If so, what's the best approach?

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• Inheritance Mapping Strategies with Entity Framework Code First CTP5: Part 3 – Table per Concrete Type (TPC) and Choosing Strategy Guidelines

  - by mortezam

  This is the third (and last) post in a series that explains different approaches to map an inheritance hierarchy with EF Code First. I've described these strategies in previous posts: Part 1 – Table per Hierarchy (TPH) Part 2 – Table per Type (TPT)In today’s blog post I am going to discuss Table per Concrete Type (TPC) which completes the inheritance mapping strategies supported by EF Code First. At the end of this post I will provide some guidelines to choose an inheritance strategy mainly based on what we've learned in this series. TPC and Entity Framework in the Past Table per Concrete type is somehow the simplest approach suggested, yet using TPC with EF is one of those concepts that has not been covered very well so far and I've seen in some resources that it was even discouraged. The reason for that is just because Entity Data Model Designer in VS2010 doesn't support TPC (even though the EF runtime does). That basically means if you are following EF's Database-First or Model-First approaches then configuring TPC requires manually writing XML in the EDMX file which is not considered to be a fun practice. Well, no more. You'll see that with Code First, creating TPC is perfectly possible with fluent API just like other strategies and you don't need to avoid TPC due to the lack of designer support as you would probably do in other EF approaches. Table per Concrete Type (TPC)In Table per Concrete type (aka Table per Concrete class) we use exactly one table for each (nonabstract) class. All properties of a class, including inherited properties, can be mapped to columns of this table, as shown in the following figure: As you can see, the SQL schema is not aware of the inheritance; effectively, we’ve mapped two unrelated tables to a more expressive class structure. If the base class was concrete, then an additional table would be needed to hold instances of that class. I have to emphasize that there is no relationship between the database tables, except for the fact that they share some similar columns. TPC Implementation in Code First Just like the TPT implementation, we need to specify a separate table for each of the subclasses. We also need to tell Code First that we want all of the inherited properties to be mapped as part of this table. In CTP5, there is a new helper method on EntityMappingConfiguration class called MapInheritedProperties that exactly does this for us. Here is the complete object model as well as the fluent API to create a TPC mapping: public abstract class BillingDetail {     public int BillingDetailId { get; set; }     public string Owner { get; set; }     public string Number { get; set; } }          public class BankAccount : BillingDetail {     public string BankName { get; set; }     public string Swift { get; set; } }          public class CreditCard : BillingDetail {     public int CardType { get; set; }     public string ExpiryMonth { get; set; }     public string ExpiryYear { get; set; } }      public class InheritanceMappingContext : DbContext {     public DbSet<BillingDetail> BillingDetails { get; set; }              protected override void OnModelCreating(ModelBuilder modelBuilder)     {         modelBuilder.Entity<BankAccount>().Map(m =>         {             m.MapInheritedProperties();             m.ToTable("BankAccounts");         });         modelBuilder.Entity<CreditCard>().Map(m =>         {             m.MapInheritedProperties();             m.ToTable("CreditCards");         });                 } } The Importance of EntityMappingConfiguration ClassAs a side note, it worth mentioning that EntityMappingConfiguration class turns out to be a key type for inheritance mapping in Code First. Here is an snapshot of this class: namespace System.Data.Entity.ModelConfiguration.Configuration.Mapping {     public class EntityMappingConfiguration<TEntityType> where TEntityType : class     {         public ValueConditionConfiguration Requires(string discriminator);         public void ToTable(string tableName);         public void MapInheritedProperties();     } } As you have seen so far, we used its Requires method to customize TPH. We also used its ToTable method to create a TPT and now we are using its MapInheritedProperties along with ToTable method to create our TPC mapping. TPC Configuration is Not Done Yet!We are not quite done with our TPC configuration and there is more into this story even though the fluent API we saw perfectly created a TPC mapping for us in the database. To see why, let's start working with our object model. For example, the following code creates two new objects of BankAccount and CreditCard types and tries to add them to the database: using (var context = new InheritanceMappingContext()) {     BankAccount bankAccount = new BankAccount();     CreditCard creditCard = new CreditCard() { CardType = 1 };                      context.BillingDetails.Add(bankAccount);     context.BillingDetails.Add(creditCard);     context.SaveChanges(); } Running this code throws an InvalidOperationException with this message: The changes to the database were committed successfully, but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: AcceptChanges cannot continue because the object's key values conflict with another object in the ObjectStateManager. Make sure that the key values are unique before calling AcceptChanges. The reason we got this exception is because DbContext.SaveChanges() internally invokes SaveChanges method of its internal ObjectContext. ObjectContext's SaveChanges method on its turn by default calls AcceptAllChanges after it has performed the database modifications. AcceptAllChanges method merely iterates over all entries in ObjectStateManager and invokes AcceptChanges on each of them. Since the entities are in Added state, AcceptChanges method replaces their temporary EntityKey with a regular EntityKey based on the primary key values (i.e. BillingDetailId) that come back from the database and that's where the problem occurs since both the entities have been assigned the same value for their primary key by the database (i.e. on both BillingDetailId = 1) and the problem is that ObjectStateManager cannot track objects of the same type (i.e. BillingDetail) with the same EntityKey value hence it throws. If you take a closer look at the TPC's SQL schema above, you'll see why the database generated the same values for the primary keys: the BillingDetailId column in both BankAccounts and CreditCards table has been marked as identity. How to Solve The Identity Problem in TPC As you saw, using SQL Server’s int identity columns doesn't work very well together with TPC since there will be duplicate entity keys when inserting in subclasses tables with all having the same identity seed. Therefore, to solve this, either a spread seed (where each table has its own initial seed value) will be needed, or a mechanism other than SQL Server’s int identity should be used. Some other RDBMSes have other mechanisms allowing a sequence (identity) to be shared by multiple tables, and something similar can be achieved with GUID keys in SQL Server. While using GUID keys, or int identity keys with different starting seeds will solve the problem but yet another solution would be to completely switch off identity on the primary key property. As a result, we need to take the responsibility of providing unique keys when inserting records to the database. We will go with this solution since it works regardless of which database engine is used. Switching Off Identity in Code First We can switch off identity simply by placing DatabaseGenerated attribute on the primary key property and pass DatabaseGenerationOption.None to its constructor. DatabaseGenerated attribute is a new data annotation which has been added to System.ComponentModel.DataAnnotations namespace in CTP5: public abstract class BillingDetail {     [DatabaseGenerated(DatabaseGenerationOption.None)]     public int BillingDetailId { get; set; }     public string Owner { get; set; }     public string Number { get; set; } } As always, we can achieve the same result by using fluent API, if you prefer that: modelBuilder.Entity<BillingDetail>()             .Property(p => p.BillingDetailId)             .HasDatabaseGenerationOption(DatabaseGenerationOption.None); Working With The Object Model Our TPC mapping is ready and we can try adding new records to the database. But, like I said, now we need to take care of providing unique keys when creating new objects: using (var context = new InheritanceMappingContext()) {     BankAccount bankAccount = new BankAccount()      {          BillingDetailId = 1                          };     CreditCard creditCard = new CreditCard()      {          BillingDetailId = 2,         CardType = 1     };                      context.BillingDetails.Add(bankAccount);     context.BillingDetails.Add(creditCard);     context.SaveChanges(); } Polymorphic Associations with TPC is Problematic The main problem with this approach is that it doesn’t support Polymorphic Associations very well. After all, in the database, associations are represented as foreign key relationships and in TPC, the subclasses are all mapped to different tables so a polymorphic association to their base class (abstract BillingDetail in our example) cannot be represented as a simple foreign key relationship. For example, consider the the domain model we introduced here where User has a polymorphic association with BillingDetail. This would be problematic in our TPC Schema, because if User has a many-to-one relationship with BillingDetail, the Users table would need a single foreign key column, which would have to refer both concrete subclass tables. This isn’t possible with regular foreign key constraints. Schema Evolution with TPC is Complex A further conceptual problem with this mapping strategy is that several different columns, of different tables, share exactly the same semantics. This makes schema evolution more complex. For example, a change to a base class property results in changes to multiple columns. It also makes it much more difficult to implement database integrity constraints that apply to all subclasses. Generated SQLLet's examine SQL output for polymorphic queries in TPC mapping. For example, consider this polymorphic query for all BillingDetails and the resulting SQL statements that being executed in the database: var query = from b in context.BillingDetails select b; Just like the SQL query generated by TPT mapping, the CASE statements that you see in the beginning of the query is merely to ensure columns that are irrelevant for a particular row have NULL values in the returning flattened table. (e.g. BankName for a row that represents a CreditCard type). TPC's SQL Queries are Union Based As you can see in the above screenshot, the first SELECT uses a FROM-clause subquery (which is selected with a red rectangle) to retrieve all instances of BillingDetails from all concrete class tables. The tables are combined with a UNION operator, and a literal (in this case, 0 and 1) is inserted into the intermediate result; (look at the lines highlighted in yellow.) EF reads this to instantiate the correct class given the data from a particular row. A union requires that the queries that are combined, project over the same columns; hence, EF has to pad and fill up nonexistent columns with NULL. This query will really perform well since here we can let the database optimizer find the best execution plan to combine rows from several tables. There is also no Joins involved so it has a better performance than the SQL queries generated by TPT where a Join is required between the base and subclasses tables. Choosing Strategy GuidelinesBefore we get into this discussion, I want to emphasize that there is no one single "best strategy fits all scenarios" exists. As you saw, each of the approaches have their own advantages and drawbacks. Here are some rules of thumb to identify the best strategy in a particular scenario: If you don’t require polymorphic associations or queries, lean toward TPC—in other words, if you never or rarely query for BillingDetails and you have no class that has an association to BillingDetail base class. I recommend TPC (only) for the top level of your class hierarchy, where polymorphism isn’t usually required, and when modification of the base class in the future is unlikely. If you do require polymorphic associations or queries, and subclasses declare relatively few properties (particularly if the main difference between subclasses is in their behavior), lean toward TPH. Your goal is to minimize the number of nullable columns and to convince yourself (and your DBA) that a denormalized schema won’t create problems in the long run. If you do require polymorphic associations or queries, and subclasses declare many properties (subclasses differ mainly by the data they hold), lean toward TPT. Or, depending on the width and depth of your inheritance hierarchy and the possible cost of joins versus unions, use TPC. By default, choose TPH only for simple problems. For more complex cases (or when you’re overruled by a data modeler insisting on the importance of nullability constraints and normalization), you should consider the TPT strategy. But at that point, ask yourself whether it may not be better to remodel inheritance as delegation in the object model (delegation is a way of making composition as powerful for reuse as inheritance). Complex inheritance is often best avoided for all sorts of reasons unrelated to persistence or ORM. EF acts as a buffer between the domain and relational models, but that doesn’t mean you can ignore persistence concerns when designing your classes. SummaryIn this series, we focused on one of the main structural aspect of the object/relational paradigm mismatch which is inheritance and discussed how EF solve this problem as an ORM solution. We learned about the three well-known inheritance mapping strategies and their implementations in EF Code First. Hopefully it gives you a better insight about the mapping of inheritance hierarchies as well as choosing the best strategy for your particular scenario. Happy New Year and Happy Code-Firsting! References ADO.NET team blog Java Persistence with Hibernate book a { color: #5A99FF; } a:visited { color: #5A99FF; } .title { padding-bottom: 5px; font-family: Segoe UI; font-size: 11pt; font-weight: bold; padding-top: 15px; } .code, .typeName { font-family: consolas; } .typeName { color: #2b91af; } .padTop5 { padding-top: 5px; } .padTop10 { padding-top: 10px; } .exception { background-color: #f0f0f0; font-style: italic; padding-bottom: 5px; padding-left: 5px; padding-top: 5px; padding-right: 5px; }

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• Load balancing and HTTPS strategies

  - by Dan

  I am faced with the following problem: Servers get saturated since current load balancing strategy is based on client IP. Some corporate clients access our servers from behind large proxies so all clients appear with same IP to our load balancer. I think we are using some hardware load balancing device (can investigate further if necessary). We need to maintain session affinity (site is constructed in ASP), so all requests with same IP get routed to the same node. Since all the communication goes over the HTTPS, no request data (like session Id) is available to balancer as a client discriminator. Is there a way to use some other data besides the IP to distinguish between clients and route the clients even when coming from same IP to different nodes? Note: I need to maintain the traffic between the balancer and nodes safe (encrypted).

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• Save open emails when exiting Outlook 2007?

  - by BigChief

  I use open emails as my todo list in Outlook 2007. For instance, when I look at my Inbox in the morning, I open all emails which I need to respond to, and throughout the day read, respond to and close each one. It's an odd system but it's how I manage my emails. Are there any addons available which will save open emails and reopen them if Outlook is restarted? I'm looking for behavior like Firefox's tabs, which will reopen each one if the process gets killed.

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• How to extract $lastexitcode from c# powershell script execution.

  - by scope-creep

  Hi, I've got a scipt executing in C# using the powershell async execution code on code project here: http://www.codeproject.com/KB/threads/AsyncPowerShell.aspx?display=PrintAll&fid=407636&df=90&mpp=25&noise=3&sort=Position&view=Quick&select=2130851#xx2130851xx I need to return the $lastexitcode and Jean-Paul describes how you can use a custom pshost class to return it. I can't find any method or property in pshost that returns the exit code. This engine I have needs to ensure that script executes correctly. Any help would be appreciated. regards Bob. Its the $lastexitcode and the $? variables I need to bring back. Hi, Finally answered. I found out about the $host variable. It implements a callback into the host, specifically a custom PSHost object, enabling you to return the $lastexitcode. Here is a link to an explanation of $host. http://mshforfun.blogspot.com/2006/08/do-you-know-there-is-host-variable.html It seems to be obscure, badly documented, as usual with powershell docs. Using point 4, calling $host.SetShouldExit(1) returns 1 to the SetShouldExit method of pshost, as described here. http://msdn.microsoft.com/en-us/library/system.management.automation.host.pshost.setshouldexit(VS.85).aspx Its really depends on defining your own exit code defintion. 0 and 1 suffixes I guess. regards Bob.

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• Running PowerShell from MSdeploy runcommand does not exit

  - by Peter Moberg

  Im am trying to get MSDeploy to execute a PowerShell script on a remote server. This is how i execute MSDeploy: msdeploy \ -verb:sync \ -source:runCommand='C:\temp\HelloWorld.bat', \ waitInterval=15000,waitAttempts=1 \ -dest:auto,computername=$WebDeployService$Credentials -verbose HelloWorld.bat contains: echo "Hello world!" powershell.exe C:\temp\WebDeploy\Package\HelloWorld.ps1 echo "Done" The HelloWorld.ps1 only contains: Write-Host "Hello world from PowerShell!" However, it seems like PowerShell never terminates. This is the output from running the msdeploy: Verbose: Performing synchronization pass #1. Verbose: Source runCommand (C:\temp\HelloWorld.bat) does not match destination (C:\temp\HelloWorld.bat) differing in attributes (isSource['True','False']). Update pending. Info: Updating runCommand (C:\temp\HelloWorld.bat). Info: Info: C:\temp>echo "Hello world!" "Hello world!" C:\temp\WebDeploy>powershell.exe C:\temp\HelloWorld.ps1 Info: Hello world from Powershell! Info: Warning: The process 'C:\Windows\system32\cmd.exe' (command line '/c "C:\Users\peter\AppData\Local\Temp\gaskgh55.b2q.bat "') is still running. Waiting for 15000 ms (attempt 1 of 1). Error: The process 'C:\Windows\system32\cmd.exe' (command line '/c "C:\Users\peter\AppData\Local\Temp\gaskgh55.b2q.bat"' ) was terminated because it exceeded the wait time. Error count: 1. Anyone knows a solution?

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• Fastest Strategy for Drawing Flash Particles

  - by user146543

  I am wondering what the fastest approach might be for using Flash/AS3 to render a 2D point plot (sonar lofargram) ; basically screens full of tiny 2D dots using Flash as fast as possible. Any suggestions on where to start? Is Flash capable of displaying 10's of thousands of 2D points (or more) with an acceptable fps?

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• Mercurial Tagging/Branching Strategy

  - by Tony Trozzo

  My current project is broken down into 3 parts: Website, Desktop Client, and a Plug-in for a third party program. We had started out originally with Subversion for our source control but decided to try Mercurial after reading Joel Spolsky's final post. Considering we haven't really used the majority of svn's potential before, we figured starting fresh with some basic ideas of how source control worked would make this transition easy. However, after setting up our initial repository, we're lost as to how tagging and branching should work on a project like this. Essentially, we're working on all 3 of these parts at the same time. We want a release to be a combination of the 3 parts. Currently we're working in one repository. For the Plug-in part, we have the first iteration finished which we've been referring to as Plug-In v0.1. For the first official build of the other two parts, we'd also like to refer to them as Website v0.1 and Desktop Client v0.1. When all three parts are at v0.1, we'd like to have a Full Project v0.1. Our problem is we're not sure how to manage all of this in the Hg repository. Would the best way to handle this be to create 3 separate repositories for the 3 stable versions and then 3 more repositories for the current developments? Currently we have this all in one repository. Should we do this in branches (are branches any different from cloning repositories?) and tags? Any help is greatly appreciated.

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• Resharper Live Template Macro that changes variable name upon exit

  - by Luhmann

  I would like to create a Resharper Live Template that changes all spaces to underscores ind my "fact" Live template variable $testname$: <Fact()> _ Public Sub $testnames$() ' Arrange $END$ ' Act ' Assert End Sub I have this: [Macro("applyRegex", ShortDescription = "Run on {#0:variable}", LongDescription = "")] class ApplyRegexMacro : IMacro { public string EvaluateQuickResult(IHotspotContext context, IList<string> arguments) { return Regex.Replace(arguments[0], " ", "_", RegexOptions.IgnoreCase); } public HotspotItems GetLookupItems(IHotspotContext context, IList<string> arguments) { return null; } public string GetPlaceholder() { return "placeholder"; } public bool HandleExpansion(IHotspotContext context, IList<string> arguments) { return false; } public ParameterInfo[] Parameters { get { return new[] { new ParameterInfo(ParameterType.String), new ParameterInfo(ParameterType.String), new ParameterInfo(ParameterType.VariableReference) }; } } } But this only runs when i press tab. I want the macro to run after I tab out of $testname$. I want to be able to just write the test name in a single line of text with spaces, and then the Macro turns all the spaces into underscores. Is this possible?

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