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• Why represent shopping carts and order invoices differently in a domain model?

  - by Todd

  I've built some shopping cart systems in the past, but I always designed them such that the final order invoice is just a shopping cart that has been marked as "purchased". All the logic for adding/removing/changing items in a cart is also the logic for the order. All data is stored in the same tables in the database. But it seems this is not the proper way to design an e-commerce site.. Can someone explain the benefit of separating the shopping cart from invoices in the domain model? It seems to me this would lead to a lot of duplicated code, an extra set of tables in the database, and make it harder to maintain in the event the system need to start accommodating more complicated orders (like specifying selected options for an item which may or may not change the price/availability/shipping time of the order). I'm assuming I just haven't seen the light, as every book and other example I see seems to separate these two seemingly similar concerns -- but I can't find any explanation as to the benefit of doing such! It's also the case in the systems that I design that changes are often made after the initial order is confirmed. It's not uncommon for items to be removed, replaced, or added afterwards (but prior to fulfillment).

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• VS2008 Link Error Using SafeInt3.hpp in 64bit mode.

  - by photo_tom

  I have the below code that links and runs fine in 32bit mode - #include "safeint3.hpp" typedef SafeInt<SIZE_T> SAFE_SIZE_T; SAFE_SIZE_T sizeOfCache; SAFE_SIZE_T _allocateAmt; Where safeint3.hpp is current version that can be found on Codeplex SafeInt. For those who are unaware of it, safeint is a template class that makes working with different integer types and sizes "safe". To quote channel 9 video on software - "it writes the code that you should". Which is my case. I have a class that is managing a large in-memory cache of objects (6gb) and I am very concerned about making sure that I don't have overflow/underflow issues on my pointers/sizes/other integer variables. In this use, it solves many problems. My problem is coming when moving from 32bit dev mode to 64bit production mode. When I build the app in this mode, I'm getting the following linker warnings - 1>cachecontrol.obj : warning LNK4006: "bool __cdecl IntrinsicMultiplyUint64(unsigned __int64 const &,unsigned __int64 const &,unsigned __int64 *)" (?IntrinsicMultiplyUint64@@YA_NAEB_K0PEA_K@Z) already defined in ImageInRamCache.obj; second definition ignored 1>cachecontrol.obj : warning LNK4006: "bool __cdecl IntrinsicMultiplyInt64(__int64 const &,__int64 const &,__int64 *)" (?IntrinsicMultiplyInt64@@YA_NAEB_J0PEA_J@Z) already defined in ImageInRamCache.obj; second definition ignored While I understand I can ignore the error, I would like either (a) prevent the warning from occurring or (b) make it disappear so that my QA department doesn't flag it as a problem. And after spending some time researching it, I cannot find a way to do either.

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• jQuery.data() works in Mac OS WebKit, but not on iPhone OS?

  - by rpj

  I'm playing around with jQTouch for an iPhone OS app that I've been toying with off and on for a while. I wanted to try my hand building it as a web app so I started playing with jQTouch. For reference, here is the page+source (all my code is currently in index.html so you can just "View Source" to see it all): http://rpj.me/doughapp.com/wd/ Essentially, I'm trying to save pertinent JSON objects retrieved from Google Local into DOM objects using the data() method (in this example, obj is the Google Local object): $('#locPane').data('selected', obj); then later (in a different "pane"), retrieving that object to be used: $('#locPane').bind('pageAnimationEnd', function(e, inf) { var selobj = $(this).data('selected'); // use 'selobj' here ... } In Chromium and Safari on the desktop OS (Snow Leopard in my case), this works perfectly (try it out). However, the same code returns undefined for the call to $(this).data('selected') in the second snippet above. I've also tried $('#' + e.target.id).data('selected') and even the naive $('#locPane').data('selected'). All variants return undefined in the iPhone OS version of WebKit, but not on the desktop. Interestingly, the running this on Mobile Safari in the iPhone Simulator fails as well. If you look at the full source, you'll see that I even try to save this object into my global jQTouch object (named jqt in my code). This, too, fails on the mobile platform. Has anyone else ever ran into this? I'll admit to not being a web/javascript programmer by trade, so if I'm making an idiot's error please call me out on it. Thank you in advance for the help! -RPJ Update: I didn't make it clear in the original post, but I'm open to any workaround if it works consistently. Since I'm having trouble storing these objects in general, anything that allows me to keep them around is good enough for now. Thanks!

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• PHP Mailer Class - Securing Email Credentials

  - by Alan A

  I am using the php mailer class to send email via my scripts. The structure is as follows: $mail = new PHPMailer; $mail->IsSMTP(); // Set mailer to use SMTP $mail->Host = 'myserver.com'; // Specify main and backup server $mail->SMTPAuth = true; // Enable SMTP authentication $mail->Username = '[email protected]'; // SMTP username $mail->Password = 'user123'; // SMTP password $mail->SMTPSecure = 'pass123'; It seems to me to be a bit of a security hole having the mailbox credentials in plain view. So I thought I might put these in an external file outside of the web root. My question is how would I then assign the $mail object these values. I of course no how to use include and/or requires... would it simple be a case of.... $mail->IsSMTP(); // Set mailer to use SMTP $mail->Host = 'myserver.com'; // Specify main and backup server $mail->SMTPAuth = true; // Enable SMTP authentication includes '../locationOutsideWebroot/emailCredntials.php'; $mail->SMTPSecure = 'pass123'; Then emailCredentails.php: <?php $mail->Username = '[email protected]'; $mail->Password = 'user123'; ?> Would this be sufficient and secure enough? Thanks, Alan.

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• Circumvent c++ null-terminated string frustration

  - by ypnos

  I'm using boost::program_options and it suffers from the same as many other c++ libs, even std itself: It still uses C-style null-terminated strings, because nobody really likes the weak std::string. The method in question is: options_description_easy_init& operator()(const char* name, const value_semantic* s, const char* description); The typical use case is just fine: options.add_options() ("graphical", bool_switch(&isGraphical)->default_value(false), "Show any graphical output during runtime") However, I need the name of the option to be set dynamically. The reason is that in some cases I nead a custom prefix, which is added to the string by my function std::string key(const std::string& k): options.add_options() (key("graphical"), bool_switch(&isGraphical)->default_value(false), "Show any graphical output during runtime") This fails. I could now use c_str() on the std::string but that's evil -- I don't know how long program_options keeps the variable around and if my string is still alive when needed. I could also reserve memory in a buffer etc. and hand in that. The buffer is never freed and it sucks/is evil. Is there anything else I can do to circumvent the C-style string mess in this situation?

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• Best way to parse this particular string using awk / sed?

  - by Jack

  Hi, I need to get a particular version string from a file (call it version.lst) and use it to compare another in a shell script. For example sake, the file contains lines that look like this: V1.000 -- build date and other info here -- APP1 V1.000 -- build date and other info here -- APP2 V1.500 -- build date and other info here -- APP3 .. and so on. Let's say I am trying to grab the first version (in this case, V1.000) from APP1. Obviously, the versions can change and I want this to be dynamic. What I have right now works: var = `cat version.lst | grep " -- APP1" | grep -Eo V[0-9].[0-9]{3}` Pipe to grep will get the line containing APP1 and the second pipe to grep will get the version string. However, I hear grep is not the way to do this so I'd like to learn the best way using awk or sed. Any ideas? I am new to both and haven't found a tutorial easy enough to learn the syntax of it. Do they support egrep? Thanks!

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• Can the Visual Studio (2010) Command Window handle "external tools" with project/solution relative p

  - by ee

  I have been playing with the Command Window in Visual Studio (View-Other Windows-Command Window). It is great for several mouse-free scenarios. (The autocompleting file "Open" command rocks in a non-trivial solution.) That success got me thinking and experimenting: Possibility 1.1: You can use the Alias commands to create custom commands Possibility 1.2: You can use the Shell command to run arbitrary executables and specify parameters (and pipe the result to the output or command windows) Possibility 2: A previously setup external tool definition (with project-relative path variables) could be run from the command window What I am stuck on is: There doesn't appear to be a way to send parameters to an aliased command (and thus the underlying Shell call) There doesn't appear to be a way to use project/solution relative paths ($SolutionDir/$ProjectDir) on a Shell call Using absolute paths in Shell works, but is fragile and high-maintenance (one alias for each needed use case). Typically you want the command to run against a file relative to your project/solution. It seems you can't run the traditional external tools (Tools-External Tools...) in the command window Ultimately I want the external tool functionality in the command window in some way. Can anyone see a way to do this? Or am I barking up the wrong tree? So my questions: Can an "external tool" of some sort (using relative project/solution path parameters) be used in the Command Window? If yes, How? If no, what might be a suitable alternative?

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• How do you make use of the provider independency in the Entity Framework?

  - by Anders Svensson

  I'm trying to learn more about data access and the Entity Framework. My goal is to have a "provider independent" data access layer (to be able to switch easily e.g. from SQL Server to MySQL or vice versa), and since the EF is supposed to be provider independent it seems like a good way to go. But how do you use this provider independence? I mean, I was expecting to be able to sort of "program to an interface", and then just be able to switch database provider. But as far as I can tell I'm only getting a concrete type to program against, an "Entities" class, e.g. in my case it is: UserDBEntities _context = new UserDBEntities(); What I would have expected to be able to switch provider easily was to have an interface e.g. like IEntities _context = new UserDBEntities(); Sort of like I can do with datasets... But maybe that isn't how it works at all with EF? Or do you just switch provider in the connectionstring, and the model stays the same?? Please remember that I'm a complete newbie at this EF, and rather inexperienced with databases in general, so I would really appreciate if you could be as clear as possible :-)

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• MySQL + Joomla + remote c# access

  - by Jimmy

  Hello, I work on a Joomla web site, installed on a MySQL database and running on IIS7. It's all working fine. I now need to add functionality that lets (Joomla-)registered users change some configuration data. Though I haven't done this yet, it looks straightforward enough to do with Joomla. The data is private so all external access will be done through HTTPS. I also need an existing c# program, running on another machine, to read that configuration data. Sure enough, this data access needs to be as fast as possible. The data will be small (and filtered by query), but the latency should be kept to a minimum. A short-term, client-side cache (less than a minute, in case a user updates his configuration data) seems like a good idea. I have done practically zero database/asp programming so far, so what's the best way of doing that last step? Should the c# program access the database 'directly' (using what? LINQ?) or setup some sort of Facade (SOAP?) service? If a service should be used, should it be done through Joomla or with ASP on IIS? Thanks

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• Managing My Database in Source Control

  - by Jason

  As I am working with a new database project (within VS2008), and as I have never developed a database from scratch, I immediately began looking into how to manage a database within source control (in this case, Subversion). I found some information on SO, including this post: Keeping development databases in multiple environments in sync. One of the answers in particular pointed to a number of a links, all of which had good, useful information. I was reading a series of posts by K. Scott Allen which describe how he manages database change. From my reading (and please pardon the noobishness of my question), it seems as though the database itself is never checked into a repository. Rather, scripts that can build the database, along with test data (which is also populated from scripts) is checked into the repository. Ultimately, this means that, when a developer is testing his or her app, these scripts, which are part of the build process, are run. This ensures that the database is up-to-date, but is also run locally from every developer's machine. This makes sense to me (if I am indeed reading that correctly). However, if I am missing something, I would appreciate correction or additional guidance. In addition, another question I wanted to ask - does this also mean that I should NOT check in the mdf or ldf files that are created from Visual Studio? Thanks for any help and additional insight. Always appreciated.

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• How to "End Task" not "Kill" or "Terminate"?

  - by Luiscencio

  Hi community. I have a 3G card to provide internet to a remote computer... I have to run a program(provided with the card) to establish the connection... since connections suddenly is lost I wrote a script that Kills the program and reopens it so that the connection is reestablished, there are certain versions of this program that don't kill the connection when killed/terminated, just when closed properly. so I am looking for a script or program that "Properly Closes" a window so I can close it and reopen it in case the connection is lost. this is the code that kills the program Option Explicit Dim objWMIService, objProcess, colProcess Dim strComputer, strProcessKill strComputer = "." strProcessKill = "'Telcel3G.exe'" Set objWMIService = GetObject("winmgmts:" _ & "{impersonationLevel=impersonate}!\\" _ & strComputer & "\root\cimv2") Set colProcess = objWMIService.ExecQuery _ ("Select * from Win32_Process Where Name = " & strProcessKill ) For Each objProcess in colProcess objProcess.Terminate() Next WSCript.Echo "Just killed process " & strProcessKill _ & " on " & strComputer WScript.Quit

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• Why does the Maven goal "package" include the resources in the jar, but the goal "jar:jar" doesnt?

  - by Bernhard V

  Hi, when I package my project with the Maven goal "package", the resources are included as well. They are originally located in the directory "src/main/resources". Because I want to create an executable jar and add the classpath to the manifest, I'm using maven-jar-plugin. I've configured it as the following likes: <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <version>2.2</version> <configuration> <archive> <manifest> <addClasspath>true</addClasspath> <mainClass>at.sozvers.stp.zpv.ekvkumsetzer.Main</mainClass> </manifest> </archive> </configuration> </plugin> Why won't the jar file created with "jar:jar" include my resources as well. As far as I'm concerned it should use the same directories as the "package" goal (which are in my case inherited from the Maven Super POM).

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• Prevent duplicate entries in arraylist

  - by timyh

  Say I create some object class like so public class thing { private String name; private Integer num; public oDetails (String a, Integer b) { name = a; num = b; } ...gets/ sets/ etc Now I want to create an arraylist to hold a number of this object class like so. ArrayList<thing> myList = new ArrayList<thing>; thing first = new thing("Star Wars", 3); thing second = new thing("Star Wars", 1); myList.add(first); myList.add(second); I would like to include some sort of logic so that in this case...when we try and add object "second" rather than add a new object to the arrayList, we add second.getNum() to first.getNum(). So if you were to iterate through the ArrayList it would be "Star Wars", 4 I am having trouble coming up with an elegant way of handling this. And as the arraylist grows, searching through it to determine if there are duplicate name items becomes cumbersome. Can anyone provide some guidance on this?

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• Margically appearing margin in footer. Could use some fresh eye's on this.

  - by Banderdash

  Hi chaps! Got a nearly finished coded comp here: http://clients.pixelbleed.net/biodesign/ I realize it's not completely valid, what with my nesting of li's and ul's within A tags. Unfortunately that's the way it has to be. My issue is with the very bottom of the footer. It has a space showing the body's background color beneath it. Tried a number of things and this space after the black link bar on the very bottom is a resistant little bugger. Ideally the black box on the bottom should rest against the very base of the view-port, at least when the content is sufficiently long--which it is in this case. If someone would like to take a quick peak at my source and give me some ideas I'd be very grateful. The CSS can be found here: http://clients.pixelbleed.net/biodesign/css/core.css And, yes, I've tried removing the height:100%. Makes no difference it seems. I do believe the issue to be with the footer, as when I remove these Div's the content rests as it should. Just don't see anything in my CSS to cause the margin/spacing issue though. Thanks so much.

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• Define "Validation in the Model"

  - by sunwukung

  There have been a couple of discussions regarding the location of user input validation: http://stackoverflow.com/questions/659950/should-validation-be-done-in-form-objects-or-the-model http://stackoverflow.com/questions/134388/where-do-you-do-your-validation-model-controller-or-view These discussions were quite old, so I wanted to ask the question again to see if anyone had any fresh input. If not, I apologise in advance. If you come from the Validation in the Model camp - does Model mean OOP representation of data (i.e. Active Record/Data Mapper) as "Entity" (to borrow the DDD terminology) - in which case you would, I assume, want all Model classes to inherit common validation constraints. Or can these rules simply be part of a Service in the Model - i.e. a Validation service? For example, could you consider Zend_Form and it's validation classes part of the Model? The concept of a Domain Model does not appear to be limited to Entities, and so validation may not necessarily need to be confined to this Entities. It seems that you would require a lot of potentially superfluous handing of values and responses back and forth between forms and "Entities" - and in some instances you may not persist the data recieved from user input, or recieve it from user input at all.

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• Cached data accessed by reference?

  - by arthurdent510

  I am running into an odd problem, and this is the only thing I can think of. I'm storing a list in cache, and I am randomly losing items from my list as users use the site. I have a class that is called that either goes to cache and returns the list from there, or if the cache is over a certain time frame old, it goes to the database and refreshes the cache. So when I pull the data from cache, this is what it looks like.... results = (List<Software>)cache["software"]; And then I return results and do some processing, filter for security, and eventually it winds up on the screen. For each Software record, there can be multiple resources attached to it, and based on how the security goes they may see some, all, or none of the records. So in the security check it will remove some of those resources from the software record. So my question is.... when I return my results list, is it a reference directly to the cache object? So when I remove a resource from the software object, it is really removing from cache as well? If that is the case, is there any way to not return it as a reference? Thanks!

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• Is this linear search implementation actually useful?

  - by Helper Method

  In Matters Computational I found this interesting linear search implementation (it's actually my Java implementation ;-)): public static int linearSearch(int[] a, int key) { int high = a.length - 1; int tmp = a[high]; // put a sentinel at the end of the array a[high] = key; int i = 0; while (a[i] != key) { i++; } // restore original value a[high] = tmp; if (i == high && key != tmp) { return NOT_CONTAINED; } return i; } It basically uses a sentinel, which is the searched for value, so that you always find the value and don't have to check for array boundaries. The last element is stored in a temp variable, and then the sentinel is placed at the last position. When the value is found (remember, it is always found due to the sentinel), the original element is restored and the index is checked if it represents the last index and is unequal to the searched for value. If that's the case, -1 (NOT_CONTAINED) is returned, otherwise the index. While I found this implementation really clever, I wonder if it is actually useful. For small arrays, it seems to be always slower, and for large arrays it only seems to be faster when the value is not found. Any ideas?

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• Speed comparison - Template specialization vs. Virtual Function vs. If-Statement

  - by Person

  Just to get it out of the way... Premature optimization is the root of all evil Make use of OOP etc. I understand. Just looking for some advice regarding the speed of certain operations that I can store in my grey matter for future reference. Say you have an Animation class. An animation can be looped (plays over and over) or not looped (plays once), it may have unique frame times or not, etc. Let's say there are 3 of these "either or" attributes. Note that any method of the Animation class will at most check for one of these (i.e. this isn't a case of a giant branch of if-elseif). Here are some options. 1) Give it boolean members for the attributes given above, and use an if statement to check against them when playing the animation to perform the appropriate action. Problem: Conditional checked every single time the animation is played. 2) Make a base animation class, and derive other animations classes such as LoopedAnimation and AnimationUniqueFrames, etc. Problem: Vtable check upon every call to play the animation given that you have something like a vector<Animation>. Also, making a separate class for all of the possible combinations seems code bloaty. 3) Use template specialization, and specialize those functions that depend on those attributes. Like template<bool looped, bool uniqueFrameTimes> class Animation. Problem: The problem with this is that you couldn't just have a vector<Animation> for something's animations. Could also be bloaty. I'm wondering what kind of speed each of these options offer? I'm particularly interested in the 1st and 2nd option because the 3rd doesn't allow one to iterate through a general container of Animations. In short, what is faster - a vtable fetch or a conditional?

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• What should I use to increase performance. View/Query/Temporary Table

  - by Shantanu Gupta

  I want to know the performance of using Views, Temp Tables and Direct Queries Usage in a Stored Procedure. I have a table that gets created every time when a trigger gets fired. I know this trigger will be fired very rare and only once at the time of setup. Now I have to use that created table from triggers at many places for fetching data and I confirms it that no one make any changes in that table. i.e ReadOnly Table. I have to use this tables data along with multiple tables to join and fetch result for further queries say select * from triggertable By Using temp table select ... into #tx from triggertable join t2 join t3 and so on select a,b, c from #tx --do something select d,e,f from #tx ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. By Using Views create view viewname ( select ... from triggertable join t2 join t3 and so on ) select a,b, c from viewname --do something select d,e,f from viewname ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. This View can be used in other places as well. So I will be creating at database rather than at sp By Using Direct Query select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something . . --and so on --around 6-7 queries in a row in a stored procedure. Now I can create a view/temporary table/ directly query usage in all upcoming queries. What would be the best to use in this case.

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• Best way to limit results in MySQL with user subcategories

  - by JM4

  I am trying to essentially solve for the following: 1) Find all users in the system who ONLY have programID 1. 2) Find all users in the system who have programID 1 AND any other active program. My tables structures (in very simple terms are as follows): users userID | Name ================ 1 | John Smith 2 | Lewis Black 3 | Mickey Mantle 4 | Babe Ruth 5 | Tommy Bahama plans ID | userID | plan | status --------------------------- 1 | 1 | 1 | 1 2 | 1 | 2 | 1 3 | 1 | 3 | 1 4 | 2 | 1 | 1 5 | 2 | 3 | 1 6 | 3 | 1 | 0 7 | 3 | 2 | 1 8 | 3 | 3 | 1 9 | 3 | 4 | 1 10 | 4 | 2 | 1 11 | 4 | 4 | 1 12 | 5 | 1 | 1 I know I can easily find all members with a specific plan with something like the following: SELECT * FROM users a JOIN plans b ON (a.userID = b.userID) WHERE b.plan = 1 AND b.status = 1 but this will only tell me which users have an 'active' plan 1. How can I tell who ONLY has plan 1 (in this case only userID 5) and how to tell who has plan 1 AND any other active plan? Update: This is not to get a count, I will actually need the original member information, including all the plans they have so a COUNT(*) response may not be what I'm trying to achieve.

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• Strange befaviour of spring transaction support for JPA + Hibernate +@Transactional annotation

  - by abovesun

  I found out really strange behavior on relatively simple use case, probably I can't understand it because of not deep knowledges of spring @Transactional nature, but this is quite interesting. I have simple User dao that extends spring JpaDaoSupport class and contains standard save method: @Transactional public User save(User user) { getJpaTemplate().persist(user); return user; } If was working fine until I've add new method to same class: User getSuperUser(), this method should return user with isAdmin == true, and if there is no super user in db, method should create one. Thats how it was looking like: public User createSuperUser() { User admin = null; try { admin = (User) getJpaTemplate().execute(new JpaCallback() { public Object doInJpa(EntityManager em) throws PersistenceException { return em.createQuery("select u from UserImpl u where u.admin = true").getSingleResult(); } }); } catch (EmptyResultDataAccessException ex) { User admin = new User('login', 'password'); admin.setAdmin(true); save(admin); // THIS IS THE POINT WHERE STRANGE THING COMING OUT } return admin; } As you see code is strange forward and I was very confused when found out that no transaction was created and committed on invocation of save(admin) method and no new user wasn't actually created despite @Transactional annotation. In result we have situation: when save() method invokes from outside of UserDAO class - @Transactional annotation counted and user successfully created, but if save() invokes from inside of other method of the same dao class - @Transactional annotation ignored. Here how I was change save() method to force it always create transaction. public User save(User user) { getJpaTemplate().execute(new JpaCallback() { public Object doInJpa(EntityManager em) throws PersistenceException { em.getTransaction().begin(); em.persist(user); em.getTransaction().commit(); return null; } }); return user; } As you see I manually invoke begin and commit. Any ideas?

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• Generating a python file

  - by fema

  Hi! I'm havin issues with python (imo python itself is an issue). I have a txt file, it contains a custom language and I have to translate it to a working python code. The input: import sys n = int(sys.argv[1]) ;;print "Beginning of the program!" LOOP i in range(1,n) {print "The number:";;print i} BRANCH n < 5 {print n ;;print "less than 5"} The wanted output looks exactly like this: import sys n = int(sys.argv[1]) print "Beginning of the program!" for i in range(1,n) : print "The number:" print i if n < 5 : print n print "less than 5" The name of the input file is read from parameter. The out file is out.py. In case of a wrong parameter, it gives an error message. The ;; means a new line. When I tried to do it, I made an array, I read all the lines into it, split by " ". Then I wanted to strip it from the marks I don't need. I made 2 loops, one for the lines, one for the words. So then I started to replace the things. Everything went fine until it came to the } mark. It finds it, but it can not replace or strip it. I have no more idea what to do. Could someone help me, please? Thanks in advance!

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• Problem with reading and writing to binary file in C++

  - by Reem

  I need to make a file that contains "name" which is a string -array of char- and "data" which is array of bytes -array of char in C++- but the first problem I faced is how to separate the "name" from the "data"? newline character could work in this case (assuming that I don't have "\n" in the name) but I could have special characters in the "data" part so there's no way to know when it ends so I'm putting an int value in the file before the data which has the size of the "data"! I tried to do this with code as follow: if((fp = fopen("file.bin","wb")) == NULL) { return false; } char buffer[] = "first data\n"; fwrite( buffer ,1,sizeof(buffer),fp ); int number[1]; number[0]=10; fwrite( number ,1,1, fp ); char data[] = "1234567890"; fwrite( data , 1, number[0], fp ); fclose(fp); but I didn't know if the "int" part was right, so I tried many other codes including this one: char buffer[] = "first data\n"; fwrite( buffer ,1,sizeof(buffer),fp ); int size=10; fwrite( &size ,sizeof size,1, fp ); char data[] = "1234567890"; fwrite( data , 1, number[0], fp ); I see 4 "NULL" characters in the file when I open it instead of seeing an integer. Is that normal? The other problem I'm facing is reading that again from the file! The code I tried to read didn't work at all :( I tried it with "fread" but I'm not sure if I should use "fseek" with it or it just read the other character after it. Forgive me but I'm a beginner :(

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• Time complexity of a powerset generating function

  - by Lirik

  I'm trying to figure out the time complexity of a function that I wrote (it generates a power set for a given string): public static HashSet<string> GeneratePowerSet(string input) { HashSet<string> powerSet = new HashSet<string>(); if (string.IsNullOrEmpty(input)) return powerSet; int powSetSize = (int)Math.Pow(2.0, (double)input.Length); // Start at 1 to skip the empty string case for (int i = 1; i < powSetSize; i++) { string str = Convert.ToString(i, 2); string pset = str; for (int k = str.Length; k < input.Length; k++) { pset = "0" + pset; } string set = string.Empty; for (int j = 0; j < pset.Length; j++) { if (pset[j] == '1') { set = string.Concat(set, input[j].ToString()); } } powerSet.Add(set); } return powerSet; } So my attempt is this: let the size of the input string be n in the outer for loop, must iterate 2^n times (because the set size is 2^n). in the inner for loop, we must iterate 2*n times (at worst). 1. So Big-O would be O((2^n)*n) (since we drop the constant 2)... is that correct? And n*(2^n) is worse than n^2. if n = 4 then (4*(2^4)) = 64 (4^2) = 16 if n = 100 then (10*(2^10)) = 10240 (10^2) = 100 2. Is there a faster way to generate a power set, or is this about optimal?

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• Immutability and shared references - how to reconcile?

  - by davetron5000

  Consider this simplified application domain: Criminal Investigative database Person is anyone involved in an investigation Report is a bit of info that is part of an investigation A Report references a primary Person (the subject of an investigation) A Report has accomplices who are secondarily related (and could certainly be primary in other investigations or reports These classes have ids that are used to store them in a database, since their info can change over time (e.g. we might find new aliases for a person, or add persons of interest to a report) If these are stored in some sort of database and I wish to use immutable objects, there seems to be an issue regarding state and referencing. Supposing that I change some meta-data about a Person. Since my Person objects immutable, I might have some code like: class Person( val id:UUID, val aliases:List[String], val reports:List[Report]) { def addAlias(name:String) = new Person(id,name :: aliases,reports) } So that my Person with a new alias becomes a new object, also immutable. If a Report refers to that person, but the alias was changed elsewhere in the system, my Report now refers to the "old" person, i.e. the person without the new alias. Similarly, I might have: class Report(val id:UUID, val content:String) { /** Adding more info to our report */ def updateContent(newContent:String) = new Report(id,newContent) } Since these objects don't know who refers to them, it's not clear to me how to let all the "referrers" know that there is a new object available representing the most recent state. This could be done by having all objects "refresh" from a central data store and all operations that create new, updated, objects store to the central data store, but this feels like a cheesy reimplementation of the underlying language's referencing. i.e. it would be more clear to just make these "secondary storable objects" mutable. So, if I add an alias to a Person, all referrers see the new value without doing anything. How is this dealt with when we want to avoid mutability, or is this a case where immutability is not helpful?

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