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• Using hashing to group similar records

  - by Neil Dobson

  I work for a fulfillment company and we have to pack and ship many orders from our warehouse to customers. To improve efficiency we would like to group identical orders and pack these in the most optimum way. By identical I mean having the same number of order lines containing the same SKUs and same order quantities. To achieve this I was thinking about hashing each order. We can then group by hash to quickly see which orders are the same. We are moving from an Access database to a PostgreSQL database and we have .NET based systems for data loading and general order processing systems, so we can either do the hashing during the data loading or hand this task over to the DB. My question firstly is should the hashing be managed by DB, possibly using triggers, or should the hash be created on-the-fly using a view or something? And secondly would it be best to calculate a hash for each order line and then to combine these to find an order-level hash for grouping, or should I just use a trigger for all CRUD operations on the order lines table which re-calculates a single hash for the entire order and store the value in the orders table? TIA

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• Component based web project directory layout with git and symlinks

  - by karlthorwald

  I am planning my directory structure for a linux/apache/php web project like this: Only www.example.com/webroot/ will be exposed in apache www.example.com/ webroot/ index.php comp1/ comp2/ component/ comp1/ comp1.class.php comp1.js comp2/ comp2.class.php comp2.css lib/ lib1/ lib1.class.php the component/ and lib/ directory will only be in the php path. To make the css and js files visible in the webroot directory I am planning to use symlinks. webroot/ index.php comp1/ comp1.js (symlinked) comp2/ comp2.css (symlinked) I tried following these principles: layout by components and libraries, not by file type and not by "public' or 'non public', index.php is an exception. This is for easier development. symlinking files that need to be public for the components and libs to a public location, but still mirroring the layout. So the component and library structure is also visible in the resulting html code in the links, which might help development. git usage should be safe and always work. it would be ok to follow some procedure to add a symlink to git, but after that checking them out or changing branches should be handled safely and clean How will git handle the symlinking of the single files correctly, is there something to consider? When it comes to images I will need to link directories, how to handle that with git? component/ comp3/ comp3.class.php img/ img1.jpg img2.jpg img3.jpg They should be linked here: webroot/ comp3/ img/ (symlinked ?) If using symlinks for that has disadvantages maybe I could move images to the webroot/ tree directly, which would break the first principle for the third (git practicability). So this is a git and symlink question. But I would be interested to hear comments about the php layout, maybe you want to use the comment function for this.

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• Correct way to do timer function in Python

  - by bwawok

  Hi. I have a GUI application that needs to do something simple in the background (update a wx python progress bar, but that doesn't really matter). I see that there is a threading.timer class.. but there seems to be no way to make it repeat. So if I use the timer, I end up having to make a new thread on every single execution... like : import threading import time def DoTheDew(): print "I did it" t = threading.Timer(1, function=DoTheDew) t.daemon = True t.start() if __name__ == '__main__': t = threading.Timer(1, function=DoTheDew) t.daemon = True t.start() time.sleep(10) This seems like I am making a bunch of threads that do 1 silly thing and die.. why not write it as : import threading import time def DoTheDew(): while True: print "I did it" time.sleep(1) if __name__ == '__main__': t = threading.Thread(target=DoTheDew) t.daemon = True t.start() time.sleep(10) Am I missing some way to make a timer keep doing something? Either of these options seems silly... I am looking for a timer more like a java.util.Timer that can schedule the thread to happen every second... If there isn't a way in Python, which of my above methods is better and why?

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• How do I debug into an ILMerged assembly?

  - by Rory Becker

  Summary I want to alter the build process of a 2-assembly solution, such that a call to ILMerge is invoked, and the build results in a single assembly. Further I would like to be able to debug into the resultant assembly. Preparation - A simple example New Solution - ClassLibrary1 Create a static function 'GetMessage' in Class1 which returns the string "Hello world" Create new console app which references the ClassLibrary. Output GetMessage from main() via the console. You now have a 2 assembly app which outputs "Hello World" to the console. So what next..? I would like to alter the Console app build process, to include a post build step which uses ILMerge, to merge the ClassLibrary assembly into the Console assembly After this step I should be able to: Run the Console app directly with no ClassLibrary1.dll present Run the Console app via F5 (or F11) in VS and be able to debug into each of the 2 projects. Limited Success I read this blogpost and managed to achieve the merge I was after with a post-build command of... "$(ProjectDir)ILMerge.bat" "$(TargetDir)" $(ProjectName) ...and an ILMerge.bat file which read... CD %1 Copy %2.exe temp.exe ILMerge.exe /out:%2.exe temp.exe ClassLibrary1.dll Del temp.exe Del ClassLibrary1.* This works fairly well, and does in fact produce an exe which runs outside the VS environment as required. However it does not appear to produce symbols (.pdb file) which VS is able to use in order to debug into the code. I think this is the last piece of the puzzle. Does anyone know how I can make this work? FWIW I am running VS2010 on an x64 Win7 x64 machine.

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• Why do WCF clients depend on the app.config file?

  - by routeNpingme

  Like a lot of things, I'm sure there's a good reason for this, so please help me understand... Why, by default, do WCF services store settings in app.config? This has been so frustrating trying to work with multiple Silverlight class libraries. These class libraries are supposed to be completely independent from each other, and this dependency on the app.config seems to cause the following headaches: Single Responsibility Principle - I should be able to add a reference to a class library and go. If that class library uses a service reference, this idea is shot before I even start coding against it. Muddy Configuration - To get other libraries to work, I have to copy and paste the service configurations into the "main" application configs. If an endpoint changes in any way, I can't just worry about a new version of that class DLL - I have to worry about anything that uses it, too. Complex Alternatives - Programmatically creating the endpoint isn't pretty. Period. There has to be a better way. Why doesn't WCF at least separate the service configurations into a ServiceName.config or something that gets copied to an output directory. What am I missing? How do you deal with this?

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• PHP Socket Server vs node.js: Web Chat

  - by Eliasdx

  I want to program a HTTP WebChat using long-held HTTP requests (Comet), ajax and websockets (depending on the browser used). Userdatabase is in mysql. Chat is written in PHP except maybe the chat stream itself which could also be written in javascript (node.js): I don't want to start a php process per user as there is no good way to send the chat messages between these php childs. So I thought about writing an own socket server in either PHP or node.js which should be able to handle more then 1000 connections (chat users). As a purely web developer (php) I'm not much familiar with sockets as I usually let web server care about connections. The chat messages won't be saved on disk nor in mysql but in RAM as an array or object for best speed. As far as I know there is no way to handle multiple connections at the same time in a single php process (socket server), however you can accept a great amount of socket connections and process them successive in a loop (read and write; incoming message - write to all socket connections). The problem is that there will most-likely be a lag with ~1000 users and mysql operations could slow the whole thing down which will then affect all users. My question is: Can node.js handle a socket server with better performance? Node.js is event-based but I'm not sure if it can process multiple events at the same time (wouldn't that need multi-threading?) or if there is just an event queue. With an event queue it would be just like php: process user after user. I could also spawn a php process per chat room (much less users) but afaik there are singlethreaded IRC servers which are also capable to handle thousands of users. (written in c++ or whatever) so maybe it's also possible in php. I would prefer PHP over Node.js because then the project would be php-only and not a mixture of programming languages. However if Node can process connections simultaneously I'd probably choose it.

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• Should methods that are required to be executed in a specific order be private?

  - by TooFat

  I have a Class that retrieves some data and images does some stuff to them and them uploads them to a third party app using web services. The object needs to perform some specific steps in order. My question is should I be explicitly exposing each method publicly like so. myObject obj = new myObject(); obj.RetrieveImages(); obj.RetrieveAssociatedData(); obj.LogIntoThirdPartyWebService(); obj.UploadStuffToWebService(); or should all of these methods be private and encapsulated in a single public method like so. public class myObject() { private void RetrieveImages(){}; private void RetrieveAssociatedData(){}; private void LogIntoThirdPartyWebService(){}; private void UploadStuffToWebService(){}; public void DoStuff() { this.RetrieveImages(); this.RetrieveAssociatedData(); this.LogIntoThirdPartyWebService(); this.UploadStuffToWebService(); } } which is called like so. myObject obj = new myObject(); obj.DoStuff();

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• .NET Regex - Replace multiple characters at once without overwriting?

  - by Everaldo Aguiar

  I'm implementing a c# program that should automatize a Mono-alphabetic substitution cipher. The functionality i'm working on at the moment is the simplest one: The user will provide a plain text and a cipher alphabet, for example: Plain text(input): THIS IS A TEST Cipher alphabet: A - Y, H - Z, I - K, S - L, E - J, T - Q Cipher Text(output): QZKL KL QJLQ I thought of using regular expressions since I've been programming in perl for a while, but I'm encountering some problems on c#. First I would like to know if someone would have a suggestion for a regular expression that would replace all occurrence of each letter by its corresponding cipher letter (provided by user) at once and without overwriting anything. Example: In this case, user provides plaintext "TEST", and on his cipher alphabet, he wishes to have all his T's replaced with E's, E's replaced with Y and S replaced with J. My first thought was to substitute each occurrence of a letter with an individual character and then replace that character by the cipherletter corresponding to the plaintext letter provided. Using the same example word "TEST", the steps taken by the program to provide an answer would be: 1 - replace T's with (lets say) @ 2 - replace E's with # 3 - replace S's with & 4 - Replace @ with E, # with Y, & with j 5 - Output = EYJE This solution doesn't seem to work for large texts. I would like to know if anyone can think of a single regular expression that would allow me to replace each letter in a given text by its corresponding letter in a 26-letter cipher alphabet without the need of splitting the task in an intermediate step as I mentioned. If it helps visualize the process, this is a print screen of my GUI for the program:

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• IIS URL Rewrite rule - Default document for subdirectories

  - by Antonio Bakula

  I would like create URL rewrite rule that will set default document for my virtual folders. eg. someting like this www.domain.com/en/ -> www.domain.com/en/index.aspx www.domain.com/hr/ -> www.domain.com/hr/index.aspx www.domain.com/de/ -> www.domain.com/de/index.aspx directories en, hr, de doesn't really exists on web server they are just markers for languange used in site used by home grown http module that will rewrite path with query params. Quick solution was define rule for every single lang, something like this : <rewrite> <rewriteMaps> <rewriteMap name="Langs"> <add key="/en" value="/en/index.aspx" /> <add key="/hr" value="/hr/index.aspx" /> <add key="/de" value="/de/index.aspx" /> </rewriteMap> </rewriteMaps> <rules> But I would really like solution that would not require changes in web.config and adding rewrite rule for every languange used on particular site. Thanks !

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• creating matrix with probabilities

  - by John Chan

  Hi all, I want to generate a matrix of NxN to test some code that I have where each row contains floats as the elements and has to add up to 1 (i.e. a row with a set of probabilities). Where it gets tricky is that I want to make sure that randomly some of the elements should be 0 (in fact most of the elements should be 0 except for some random ones to be the probabilities). I need the probabilities to be 1/m where m is the number of elements that are not 0 within a single row. I tried to think of ways to output this, but essentially I would need this stored in a C++ array. So even if I output to a file I would still have the issue of not having it in array as I need it. At the end of it all I need that array because I want to generate a Market Matrix file. I found an implementation in C++ to take an array and convert it to the market matrix file, so this is what I am basing my findings on. My input for the rest of the code takes in this market matrix file so I need that to be the primary form of output. The language does not matter, I just want to generate the file at the end (I found a way mmwrite and mmread in python as well) Please help, I am stuck and not really sure how to implement this.

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• JDBC transaction dead-lock solution required?

  - by user49767

  It's a scenario described my friend and challenged to find solution. He is using Oracle database and JDBC connection with read committed as transaction isolation level. In one of the transaction, he updates a record and executes selects statement and commits the transaction. when everything happening within single thread, things are fine. But when multiple requests are handled, dead-lock happens. Thread-A updates a record. Thread B updates another record. Thread-A issues select statement and waits for Thread-B's transaction to complete the commit operation. Thread-B issues select statement and waits for Thread-A's transaction to complete the commit operation. Now above causes dead-lock. Since they use command pattern, the base framework allows to issue commit only once (at the end of all the db operation), so they are unable to issue commit immediately after select statement. My argument was Thread-A supposed to select all the records which are committed and hence should not be issue. But he said that Thread-A will surely wait till Thread-B commits the record. is that true? What are all the ways, to avoid the above issue? is it possible to change isolation-level? (without changing underlying java framework) Little information about base framework, it is something similar to Struts action, their each and every request handled by one action, transaction begins before execution and commits after execution.

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• How to implement generic callbacks in C++

  - by Kylotan

  Forgive my ignorance in asking this basic question but I've become so used to using Python where this sort of thing is trivial that I've completely forgotten how I would attempt this in C++. I want to be able to pass a callback to a function that performs a slow process in the background, and have it called later when the process is complete. This callback could be a free function, a static function, or a member function. I'd also like to be able to inject some arbitrary arguments in there for context. (ie. Implementing a very poor man's coroutine, in a way.) On top of that, this function will always take a std::string, which is the output of the process. I don't mind if the position of this argument in the final callback parameter list is fixed. I get the feeling that the answer will involve boost::bind and boost::function but I can't work out the precise invocations that would be necessary in order to create arbitrary callables (while currying them to just take a single string), store them in the background process, and invoke the callable correctly with the string parameter.

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• Importing into a Exported object with MEF

  - by Nathan W

  I'm sorry if this question has already been asked 100 times, but I'm really struggling to get it to work. Say I have have three projects. Core.dll Has common interfaces Shell.exe Loads all modules in assembly folder. References Core.dll ModuleA.dll Exports Name, Version of module. References Core.dll Shell.exe has a [Export] that contains an single instance of a third party application that I need to inject into all loaded modules. So far the code that I have in Shell.exe is: static void Main(string[] args) { ThirdPartyApp map = new ThirdPartyApp(); var ad = new AssemblyCatalog(Assembly.GetExecutingAssembly()); var dircatalog = new DirectoryCatalog("."); var a = new AggregateCatalog(dircatalog, ad); // Not to sure what to do here. } class Test { [Export(typeof(ThirdPartyApp))] public ThirdPartyApp Instance { get; set; } [Import(typeof(IModule))] public IModule Module { get; set; } } I need to create a instance of Test, and load Instance with map from the Main method then load the Module from ModuleA.dll that is in the executing directory then [Import] Instance into the loaded module. In ModuleA I have a class like this: [Export(IModule)] class Module : IModule { [Import(ThirdPartyApp)] public ThirdPartyApp Instance {get;set;} } I know I'm half way there I just don't know how to put it all together, mainly with loading up test with a instance of map from Main. Could anyone help me with this.

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• functions with same names in javascript

  - by biju

  Hi, I tried to write a function on a js file and another function with the same name in the page.I expected an error but no error came and i got only the function from the js file to execute.How is this possible.Even if i write a function in a separate js file,everything is rendered in a single html file.Then how come it is possible <script type="text/javascript" language="javascript" src="JScript.js" /> <script language="javascript"> function Boo() { alert("Hai new"); } </script> <head runat="server"> <title></title> </head> <body> <form id="form1" runat="server"> <div> <asp:Button runat=server OnClientClick="Boo();" Text="Click" /> </div> </form> </body> and in the js file function Boo() { alert("Hai"); }

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• Generate and download a text file in javascript

  - by Mark B

  All my research so far suggests this can't be done, but I'm hoping someone here has some cunning ideas. I have a form on a website which allows users to bulk upload lots of URLs to add to a list on the server. There's quite a lot of server-side processing to do on each URL, so to avoid timeouts and to display progress, I've implemented the upload using jQuery to submit the URLs one at a time using ajax. This is all working nicely. However, part of the processing on each URL is deduplicating it against the complete list. The ajax call returns a status indicating either a successful upload or a rejection due to duplication. As the upload progresses, I tell the user how many URLs have been rejected as duplicates (along with overall progress and ETA). The problem now is how to give the user a complete list of the failed duplicate URLs. I've kept them in an array in my jQuery, and would like the user to be able to click on a link on the form to download a text file containing those URLs. Is this possible just using client-side processing? The server-side processing basically handles a single keyword at a time. I'd rather not have to store the duplicates in a database table with some kind of session key which gets sent with every ajax call, and is then used at the end to generate the text file server-side (and then gets cleaned up some time later). I can see how to do this, but it seems very clunky and a bit 20th century.

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• Jboss 6 Cluster Singleton Clustered

  - by DanC

  I am trying to set up a Jboss 6 in a clustered environment, and use it to host clustered stateful singleton EJBs. So far we succesfully installed a Singleton EJB within the cluster, where different entrypoints to our application (through a website deployed on each node) point to a single environment on which the EJB is hosted (thus mantaining the state of static variables). We achieved this using the following configuration: Bean interface: @Remote public interface IUniverse { ... } Bean implementation: @Clustered @Stateful public class Universe implements IUniverse { private static Vector<String> messages = new Vector<String>(); ... } jboss-beans.xml configuration: <deployment xmlns="urn:jboss:bean-deployer:2.0"> <!-- This bean is an example of a clustered singleton --> <bean name="Universe" class="Universe"> </bean> <bean name="UniverseController" class="org.jboss.ha.singleton.HASingletonController"> <property name="HAPartition"><inject bean="HAPartition"/></property> <property name="target"><inject bean="Universe"/></property> <property name="targetStartMethod">startSingleton</property> <property name="targetStopMethod">stopSingleton</property> </bean> </deployment> The main problem for this implementation is that, after the master node (the one that contains the state of the singleton EJB) shuts down gracefuly, the Singleton's state is lost and reset to default. Please note that everything was constructed following the JBoss 5 Clustering documents, as no JBoss 6 documents were found on this subject. Any information on how to solve this problem or where to find JBoss 6 documention on clustering is appreciated.

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• How do I relate two models/tables in Django based on non primary non unique keys?

  - by wizard

  I've got two tables that I need to relate on a single field po_num. The data is imported from another source so while I have a little bit of control over what the tables look like but I can't change them too much. What I want to do is relate these two models so I can look up one from the other based on the po_num fields. What I really need to do is join the two tables so I can do a where on a count of the related table. I would like to do filter for all Order objects that have 0 related EDI856 objects. I tried adding a foreign key to the Order model and specified the db_column and to_fields as po_num but django didn't like that the fact that Edi856.po_num wasn't unique. Here are the important fields of my current models that let me display but not filter for the data that I want. class Edi856(models.Model): po_num = models.CharField(max_length=90, db_index=True ) class Order(models.Model): po_num = models.CharField(max_length=90, db_index=True) def in_edi(self): '''Has the edi been processed?''' return Edi856.objects.filter(po_num = self.po_num).count() Thanks for taking the time to read about my problem. I'm not sure what to do from here.

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• Keeping sync in multiplayer RTS game that uses floating point arithmetic

  - by Calmarius

  I'm writing a 2D space RTS game in C#. Single player works. Now I want to add some multiplayer functionality. I googled for it and it seems there is only one way to have thousands of units continuously moving without a powerful net connection: send only the commands through the network while running the same simulation at every player. And now there is a problem the entire engine uses doubles everywhere. And floating point calculations are depends heavily on compiler optimalizations and cpu architecture so it is very hard to keep things syncronized. And it is not grid based at all, and have a simple phisics engine to move the space-ships (space ships have impulse and angular-momentum...). So recoding the entire stuff to use fixed point would be quite cumbersome (but probably the only solution). So I have 2 options so far: Say bye to the current code and restart from scratch using integers Make the game LAN only where there is enough bandwidth to have 8 players with thousands of units and sending the positions and orientation etc in (almost) every frame... So I looking for better opinions, (or even tips on migrating the code to fixed-point without messing everything up...)

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• Why might my PHP log file not entirely be text?

  - by Fletcher Moore

  I'm trying to debug a plugin-bloated Wordpress installation; so I've added a very simple homebrew logger that records all the callbacks, which are basically listed in a single, ultimately 250+ row multidimensional array in Wordpress (I can't use print_r() because I need to catch them right before they are called). My logger line is $logger->log("\t" . $callback . "\n"); The logger produces a dandy text file in normal situations, but at two points during this particular task it is adding something which causes my log file to no longer be encoded properly. Gedit (I'm on Ubuntu) won't open the file, claiming to not understand the encoding. In vim, the culprit corrupt callback (which I could not find in the debugger, looking at the array) is about in the middle and printed as ^@lambda_546 and at the end of file there's this cute guy ^M. The ^M and ^@ are blue in my vim, which has no color theme set for .txt files. I don't know what it means. I tried adding an is_string($callback) condition, but I get the same results. Any ideas?

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• alternative to #include within namespace { } block

  - by Jeff

  Edit: I know that method 1 is essentially invalid and will probably use method 2, but I'm looking for the best hack or a better solution to mitigate rampant, mutable namespace proliferation. I have multiple class or method definitions in one namespace that have different dependencies, and would like to use the fewest namespace blocks or explicit scopings possible but while grouping #include directives with the definitions that require them as best as possible. I've never seen any indication that any preprocessor could be told to exclude namespace {} scoping from #include contents, but I'm here to ask if something similar to this is possible: (see bottom for explanation of why I want something dead simple) // NOTE: apple.h, etc., contents are *NOT* intended to be in namespace Foo! // would prefer something most this: namespace Foo { #include "apple.h" B *A::blah(B const *x) { /* ... */ } #include "banana.h" int B::whatever(C const &var) { /* ... */ } #include "blueberry.h" void B::something() { /* ... */ } } // namespace Foo ... // over this: #include "apple.h" #include "banana.h" #include "blueberry.h" namespace Foo { B *A::blah(B const *x) { /* ... */ } int B::whatever(C const &var) { /* ... */ } void B::something() { /* ... */ } } // namespace Foo ... // or over this: #include "apple.h" namespace Foo { B *A::blah(B const *x) { /* ... */ } } // namespace Foo #include "banana.h" namespace Foo { int B::whatever(C const &var) { /* ... */ } } // namespace Foo #include "blueberry.h" namespace Foo { void B::something() { /* ... */ } } // namespace Foo My real problem is that I have projects where a module may need to be branched but have coexisting components from the branches in the same program. I have classes like FooA, etc., that I've called Foo::A in the hopes being able to branch less painfully as Foo::v1_2::A, where some program may need both a Foo::A and a Foo::v1_2::A. I'd like "Foo" or "Foo::v1_2" to show up only really once per file, as a single namespace block, if possible. Moreover, I tend to prefer to locate blocks of #include directives immediately above the first definition in the file that requires them. What's my best choice, or alternatively, what should I be doing instead of hijacking the namespaces?

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• Selenium Webdriver Java - looking for alternatives for Actions and Robot when performing drag-and-drop

  - by Ja-ke Alconcel

  I first tried Actions class and the drag-and-drop does work on different elements, however it was unable to locate the a specific draggable element on it's exact screen/webpage position. Here's the code I've used: Point loc = driver.findElement(By.id("thiselement")).getLocation(); System.out.println(loc); WebElement drag = driver.findElement(By.id("thiselement")); Actions test = new Actions(driver); test.dragAndDropBy(drag, 0, 60).build().perform(); I checked the element with it's pixel location and it prints (837, -52), which was somewhere on top of the webpage and was pixels away from the actual element. Then I tried using the Robot class and works perfectly fine on my script, but can only provide constant successful runs on a single test machine, running it with a different machine with different screen resolution and screen size will render the script to fail due to the dependency of Robot on the pixel location of the element. The sample code of the Robot script I'm using: Robot dragAndDrop = new Robot(); dragAndDrop.mouseMove(945, 166); //actual pixel location of the draggable element dragAndDrop.mousePress(InputEvent.BUTTON1_MASK); sleep(3000); dragAndDrop.mouseMove(945, 226); dragAndDrop.mouseRelease(InputEvent.BUTTON1_MASK); sleep(3000); Is there any alternative for Actions and Robot to automate drag-and-drop? Or maybe a help on working the script to work on Actions as I really can't use Robot. Thanks in advance.

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• Group / User based security. Table / SQL question

  - by Brett

  Hi, I'm setting up a group / user based security system. I have 4 tables as follows: user groups group_user_mappings acl where acl is the mapping between an item_id and either a group or a user. The way I've done the acl table, I have 3 columns of note (actually 4th one as an auto-id, but that is irrelevant) col 1 item_id (item to access) col 3 user_id (user that is allowed to access) col 3 group_id (group that is allowed to access) So for example item1, peter, , item2, , group1 item3, jane, , so either the acl will give access to a user or a group. Any one line in the ACL table with either have an item - user mapping, or an item group. If I want to have a query that returns all objects a user has access to, I think I need to have a SQL query with a UNION, because I need 2 separate queries that join like.. item - acl - group - user AND item - acl - user This I guess will work OK. Is this how its normally done? Am I doing this the right way? Seems a little messy. I was thinking I could get around it by creating a single user group for each person, so I only ever deal with groups in my SQL, but this seems a little messy as well..

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• What's the next steps for moving from appengine to full django?

  - by tomcritchlow

  Hey guys, I'm super new to programming and I've been using appengine to help me learn python and general coding. I'm getting better quickly and I'm loving it all the way :) Appengine was awesome for allowing me to just dive into writing my app and getting something live that works (see http://www.7bks.com/). But I'm realising that the longer I continue to learn on appengine the more I'm constraining myself and locking myself into a single system. I'd like to move to developing on full django (since django looks super cool!). What are my next steps? To give you a feel for my level of knowledge: I'm not a unix user I'm not familiar with command line controls (I still use appengine/python completely via the appengine SDK) I've never programmed in anything other than python, anywhere other than appengine I know the word SQL, but don't know what MySQL is really or how to use it. So, specifically: What are the skills I need to learn to get up and running with full django/python? If I'm going to host somewhere else I suppose I'll need to learn some sysadmin type skills (maybe even unix?). Is there anywhere that offers easy hosting (like appengine) but that supports django? I hear such great things about heroku I'm considering switching to RoR and going there I appreciate that I'm likely not quite ready to move away from appengine just yet but I'm a fiercely passionate learner (http://www.7bks.com/blog/179001) and would love it if I knew all the steps I needed to learn so I could set about learning them. At the moment, I don't even know what the steps are I need to learn! Thank you very much. Sorry this isn't a specific programming question but I've looked around and haven't found a good how-to for someone of my level of experience and I think others would appreciate a good roadmap for the things we need to learn to get up and running. Thanks, Tom PS - if anyone is in London and fancies showing me the ropes in person that would be super awesome :)

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• How to exclude rows where matching join is in an SQL tree

  - by Greg K

  Sorry for the poor title, I couldn't think how to concisely describe this problem. I have a set of items that should have a 1-to-1 relationship with an attribute. I have a query to return those rows where the data is wrong and this relationship has been broken (1-to-many). I'm gathering these rows to fix them and restore this 1-to-1 relationship. This is a theoretical simplification of my actual problem but I'll post example table schema here as it was requested. item table: +------------+------------+-----------+ | item_id | name | attr_id | +------------+------------+-----------+ | 1 | BMW 320d | 20 | | 1 | BMW 320d | 21 | | 2 | BMW 335i | 23 | | 2 | BMW 335i | 34 | +------------+------------+-----------+ attribute table: +---------+-----------------+------------+ | attr_id | value | parent_id | +---------+-----------------+------------+ | 20 | SE | 21 | | 21 | M Sport | 0 | | 23 | AC | 24 | | 24 | Climate control | 0 | .... | 34 | Leather seats | 0 | +---------+-----------------+------------+ A simple query to return items with more than one attribute. SELECT item_id, COUNT(DISTINCT(attr_id)) AS attributes FROM item GROUP BY item_id HAVING attributes > 1 This gets me a result set like so: +-----------+------------+ | item_id | attributes | +-----------+------------+ | 1 | 2 | | 2 | 2 | | 3 | 2 | -- etc. -- However, there's an exception. The attribute table can hold a tree structure, via parent links in the table. For certain rows, parent_id can hold the ID of another attribute. There's only one level to this tree. Example: +---------+-----------------+------------+ | attr_id | value | parent_id | +---------+-----------------+------------+ | 20 | SE | 21 | | 21 | M Sport | 0 | .... I do not want to retrieve items in my original query where, for a pair of associated attributes, they related like attributes 20 & 21. I do want to retrieve items where: the attributes have no parent for two or more attributes they are not related (e.g. attributes 23 & 34) Example result desired, just the item ID: +------------+ | item_id | +------------+ | 2 | +------------+ How can I join against attributes from items and exclude these rows? Do I use a temporary table or can I achieve this from a single query? Thanks.

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• FreqTable with random values(#C)

  - by Sef

  Hello, I would like to make a frequency table with random numbers. So i have created a array that generates 11 random values between 0 and 9999. public void FillArrayRandom(int[] T) { Random Rndint = new Random(); for (int i=0; i < T.Length; i++) { T[i] = Rndint.Next(0, 9999); } }/*FillArrayRandom*/ The result i want is something alike this:(bar height up to 21) So this will be a constant. * * * * * * (the highest value will have the largest row/bar) * * * * 0 1 2 3 .....(index value's) 931 6669 10 8899 .... (up to 11 random values) My question is how do i exactly caculate the frequency between those 11 random values? The bars should have a relative relation with each other depending on there frequency. I would only like to use 1 single array in my program (for the generated values). F = (F * 21?) / ...? Really no clue how to obtain the proper results. If a frequency is =21 write * If a frequency is =20 write * If a frequency is =19 write * etc... Regards.

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