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• Scalability 101: How can I design a scalable web application using PHP?

  - by Legend

  I am building a web-application and have a couple of quick questions. From what I learnt, one should not worry about scalability when initially building the app and should only start worrying when the traffic increases. However, this being my first web-application, I am not quite sure if I should take an approach where I design things in an ad-hoc manner and later "fix" them. I have been reading stories about how people start off with an app that gets millions of users in a week or two. Not that I will face the same situation but I can't help but wonder, how do these people do it? Currently, I bought a shared hosting account on Lunarpages and that got me started in building and testing the application. However, I am interested in learning how to build the same application in a scalable-manner using the cloud, for instance, Amazon's EC2. From my understanding, I can see a couple of components: There is a load balancer that first receives requests and then decides where to route each request This request is then handled by a server replica that then processes the request and updates (if required) the database and sends back the response to the client If a similar request comes in, then a caching mechanism like memcached kicks into picture and returns objects from the cache A blackbox that handles database replication Specifically, I am trying to do the following: Setting up a load balancer (my homework revealed that HAProxy is one such load balancer) Setting up replication so that databases can be synchronized Using memcached Configuring Apache to work with multiple web servers Partitioning application to use Amazon EC2 and Amazon S3 (my application is something that will need great deal of storage) Finally, how can I avoid burning myself when using Amazon services? Because this is just a learning phase, I can probably do with 2-3 servers with a simple load balancer and replication but until I want to avoid paying loads of money accidentally. I am able to find resources on individual topics but am unable to find something that starts off from the big picture. Can someone please help me get started?

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• How to test a Grails Service that utilizes a criteria query (with spock)?

  - by user569825

  I am trying to test a simple service method. That method mainly just returns the results of a criteria query for which I want to test if it returns the one result or not (depending on what is queried for). The problem is, that I am unaware of how to right the corresponding test correctly. I am trying to accomplish it via spock, but doing the same with any other way of testing also fails. Can one tell me how to amend the test in order to make it work for the task at hand? (BTW I'd like to keep it a unit test, if possible.) The EventService Method public HashSet<Event> listEventsForDate(Date date, int offset, int max) { date.clearTime() def c = Event.createCriteria() def results = c { and { le("startDate", date+1) // starts tonight at midnight or prior? ge("endDate", date) // ends today or later? } maxResults(max) order("startDate", "desc") } return results } The Spock Specification package myapp import grails.plugin.spock.* import spock.lang.* class EventServiceSpec extends Specification { def event def eventService = new EventService() def setup() { event = new Event() event.publisher = Mock(User) event.title = 'et' event.urlTitle = 'ut' event.details = 'details' event.location = 'location' event.startDate = new Date(2010,11,20, 9, 0) event.endDate = new Date(2011, 3, 7,18, 0) } def "list the Events of a specific date"() { given: "An event ranging over multiple days" when: "I look up a date for its respective events" def results = eventService.listEventsForDate(searchDate, 0, 100) then: "The event is found or not - depending on the requested date" numberOfResults == results.size() where: searchDate | numberOfResults new Date(2010,10,19) | 0 // one day before startDate new Date(2010,10,20) | 1 // at startDate new Date(2010,10,21) | 1 // one day after startDate new Date(2011, 1, 1) | 1 // someday during the event range new Date(2011, 3, 6) | 1 // one day before endDate new Date(2011, 3, 7) | 1 // at endDate new Date(2011, 3, 8) | 0 // one day after endDate } } The Error groovy.lang.MissingMethodException: No signature of method: static myapp.Event.createCriteria() is applicable for argument types: () values: [] at myapp.EventService.listEventsForDate(EventService.groovy:47) at myapp.EventServiceSpec.list the Events of a specific date(EventServiceSpec.groovy:29)

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• Link compatibility between C++ and D

  - by Caspin

  D easily interfaces with C. D just as easily interfaces with C++, but (and it's a big but) the C++ needs to be extremely trivial. The code cannot use: namespaces templates multiple inheritance mix virtual with non-virtual methods more? I completely understand the inheritance restriction. The rest however, feel like artificial limitations. Now I don't want to be able to use std::vector<T> directly, but I would really like to be able to link with std::vector<int> as an externed template. The C++ interfacing page has this particularly depressing comment. D templates have little in common with C++ templates, and it is very unlikely that any sort of reasonable method could be found to express C++ templates in a link-compatible way with D. This means that the C++ STL, and C++ Boost, likely will never be accessible from D. Admittedly I'll probably never need std::vector while coding in D, but I'd love to use QT or boost. So what's the deal. Why is it so hard to express non-trivial C++ classes in D? Would it not be worth it to add some special annotations or something to express at least namespaces?

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• a reusable query with modifications?

  - by fusion

  i'm using this mysql query alongwith php to search for multiple keywords: $query = "SELECT cQuotes, vAuthor, cArabic, vReference FROM ".$table." WHERE ("; $countFields = count($arrayFields); while ($a < $countFields) { while ($b < $countSearch) { $query = $query."$arrayFields[$a] LIKE '%$arraySearch[$b]%'"; $b++; if ($b < $countSearch) { $query = $query." AND "; } } $b = 0; $a++; if ($a < $countFields) { $query = $query.") OR ("; } } $query = $query.")"; $result = mysql_query($query, $conn) i'd like to reuse this query with a few modifications to it (for instance, the WHERE clause remains the same, while i query the number of rows using COUNT), but it doesn't seem practical to repeat the code again for a few additions. any suggestions?

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• Thread mutex behaviour

  - by Alberteddu

  Hi there, I'm learning C. I'm writing an application with multiple threads; I know that when a variable is shared between two or more threads, it is better to lock/unlock using a mutex to avoid deadlock and inconsistency of variables. This is very clear when I want to change or view one variable. int i = 0; /** Global */ static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /** Thread 1. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); /** Thread 2. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); This is correct, I think. The variable i, at the end of the executions, contains the integer 2. Anyway, there are some situations in which I don't know exactly where to put the two function calls. For example, suppose you have a function obtain(), which returns a global variable. I need to call that function from within the two threads. I have also two other threads that call the function set(), defined with a few arguments; this function will set the same global variable. The two functions are necessary when you need to do something before getting/setting the var. /** (0) */ /** Thread 1, or 2, or 3... */ if(obtain() == something) { if(obtain() == somethingElse) { // Do this, sometimes obtain() and sometimes set(random number) (1) } else { // Do that, just obtain(). (2) } } else { // Do this and do that (3) // If # of thread * 3 > 10, then set(3*10) For example. (4) } /** (5) */ Where I have to lock, and where I have to unlock? The situation can be, I think, even more complex. I will appreciate an exhaustive answer. Thank you in advance. —Alberto

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• How can I change jtable height at runtime

  - by wniroshan

  I hava a JFrame with multiple JPanels of similar width aligned one below other. I use one of these JPanels to display a JTable which is the last JPanel of the lot. This JPanel has a JScrollpane as a child component. This is where I try to add my table dynamically. Initial height of this JScrollpane is set to 40. I designed above template using Netbeans 6.8 Now I'm trying to add the table to the JPanel. When a button is pressed below code snippet is called. The class which includes this code extends javax.swing.JFrame class. I am expecting below code would adjust table height according to the row count and display the table. SearchTable = new JTable(RowData, DisplayNames) { @Override public boolean isCellEditable(int rowIndex, int vColIndex) { return false; } }; // if row count is less than 10 then display all the rows without a scroll bar if (SearchTable.getRowCount() < 10) { pnl_tblpanel.setPreferredSize(new Dimension(625, SearchTable.getRowHeight() * (SearchTable.getRowCount() + 4))); scr_tblholder.setPreferredSize(new Dimension(625, SearchTable.getRowHeight() * (SearchTable.getRowCount() + 4))); } else {// if row count is more than 10 display first 10 rows and add a scroll bar pnl_tblpanel.setPreferredSize(new Dimension(625, SearchTable.getRowHeight() * (10 + 2))); scr_tblholder.setAutoscrolls(true); } //pnl_tblpanel.add(scr_tblholder); scr_tblholder.setViewportView(SearchTable); //pnl_tblpanel.repaint(); pnl_tblpanel.validate(); this.validate(); //this.repaint(); pnl_tblpanel.setVisible(true); this.pack(); The table displays, but the table height is not changed according to the row count. It stays its default value. I have been trying many combinations of validate and repaint but nothing worked. (More in desperation) Can anyone shed some light on this Thank you

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• Binding Listbox item source to a collection of collections in windows phone 7

  - by Tee

  Hi there, I am trying to bind a Listbox ItemSource to a collection of multiple Lists. i.e. List PersonCollection List Person List Collection Now I need to show items from both of these list. In wpf you could use HierarchicalDataTemplate i believe, but not sure how I can do it in windows phone 7. Tried with Blend and it generates the following data template. <DataTemplate x:Key="PersonDataTemplate"> <Grid> <StackPanel Margin="0,0,1,0" Orientation="Vertical" VerticalAlignment="Top"> <TextBlock Margin="0,0,1,0" TextWrapping="Wrap" Text="{Binding Person[0].Name}" d:LayoutOverrides="Width"/> <TextBlock Margin="0,0,1,0" TextWrapping="Wrap" Text="{Binding Collection[0].Total}" d:LayoutOverrides="Width"/> </StackPanel> </Grid> </DataTemplate> Is there another way I can do this? I have tried to set the DataContext of Textbox in DataTemplate to individual arrays but did not seem to work. Cant find anything similar on the net apart from the confirmation that HierarchicalDataTemplate is not supported in Windows Phone 7. I have other ways to do but none elegant.. Thanks in advance. Regards

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• Appropriate use of die()?

  - by letseatfood

  I create pages in my current PHP project by using the following template: <?php include 'bootstrap.php'; head(); ?> <!-- Page content here --> <?php foot(); ?> Is the following example an appropriate use of die()? Also, what sort of problems might this cause for me, if any? <?php include 'bootstrap.php'; head(); try { //Simulate throwing an exception from some class throw new Exception('Something went wrong!'); } catch(Exception $e) { ?> <p>Please fix the following errors:</p> <p><?php echo $e->getMessage(); ?></p> <?php foot(); die(); } //If no exception is thrown above, continue script doSomething(); doSomeOtherThing(); foot(); ?> ?> <?php foot(); ?> Basically, I have a script with multiple tasks on it and I am trying to set up a graceful way to notify the user of input errors while preventing the remaining portion of the script from executing. Thanks!

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• Unit Testing - Algorithm or Sample based ?

  - by ohadsc

  Say I'm trying to test a simple Set class public IntSet : IEnumerable<int> { Add(int i) {...} //IEnumerable implementation... } And suppose I'm trying to test that no duplicate values can exist in the set. My first option is to insert some sample data into the set, and test for duplicates using my knowledge of the data I used, for example: //OPTION 1 void InsertDuplicateValues_OnlyOneInstancePerValueShouldBeInTheSet() { var set = new IntSet(); //3 will be added 3 times var values = new List<int> {1, 2, 3, 3, 3, 4, 5}; foreach (int i in values) set.Add(i); //I know 3 is the only candidate to appear multiple times int counter = 0; foreach (int i in set) if (i == 3) counter++; Assert.AreEqual(1, counter); } My second option is to test for my condition generically: //OPTION 2 void InsertDuplicateValues_OnlyOneInstancePerValueShouldBeInTheSet() { var set = new IntSet(); //The following could even be a list of random numbers with a duplicate var values = new List<int> { 1, 2, 3, 3, 3, 4, 5}; foreach (int i in values) set.Add(i); //I am not using my prior knowledge of the sample data //the following line would work for any data CollectionAssert.AreEquivalent(new HashSet<int>(values), set); } Of course, in this example, I conveniently have a set implementation to check against, as well as code to compare collections (CollectionAssert). But what if I didn't have either ? This is the situation when you are testing your real life custom business logic. Granted, testing for expected conditions generically covers more cases - but it becomes very similar to implementing the logic again (which is both tedious and useless - you can't use the same code to check itself!). Basically I'm asking whether my tests should look like "insert 1, 2, 3 then check something about 3" or "insert 1, 2, 3 and check for something in general" EDIT - To help me understand, please state in your answer if you prefer OPTION 1 or OPTION 2 (or neither, or that it depends on the case, etc )

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• How can I manage building library projects that produce both a static lib and a dll?

  - by Scott Langham

  I've got a large visual studio solution with ~50 projects. There are configurations for StaticDebug, StaticRelease, Debug and Release. Some libraries are needed in both dll and static lib form. To get them, we rebuild the solution with a different configuration. The Configuration Manager window is used to setup which projects need to build in which flavours, static lib, dynamic dll or both. This can by quite tricky to manage and it's a bit annoying to have to build the solution multiple times and select the configurations in the right order. Static versions need building before non-static versions. I'm wondering, instead of this current scheme, might it be simpler to manage if, for the projects I needed to produce both a static lib and dynamc dll, I created two projects. Eg: CoreLib CoreDll I could either make both of these projects reference all the same files and build them twice, or I'm wondering, would it be possible to build CoreLib and then get CoreDll to link it to generate the dll? I guess my question is, do you have any advice on how to structure your projects in this kind of situation? Thanks.

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• Prototyping Qt/C++ in Python

  - by tstenner

  I want to write a C++ application with Qt, but build a prototype first using Python and then gradually replace the Python code with C++. Is this the right approach, and what tools (bindings, binding generators, IDE) should I use? Ideally, everything should be available in the Ubuntu repositories so I wouldn't have to worry about incompatible or old versions and have everything set up with a simple aptitude install. Is there any comprehensive documentation about this process or do I have to learn every single component, and if yes, which ones? Right now I have multiple choices to make: Qt Creator, because of the nice auto completion and Qt integration. Eclipse, as it offers support for both C++ and Python. Eric (haven't used it yet) Vim PySide as it's working with CMake and Boost.Python, so theoretically it will make replacing python code easier. PyQt as it's more widely used (more support) and is available as a Debian package. Edit: As I will have to deploy the program to various computers, the C++-solution would require 1-5 files (the program and some library files if I'm linking it statically), using Python I'd have to build PyQt/PySide/SIP/whatever on every platform and explain how to install Python and everything else.

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• What are the Limitations for Connecting to an Access Query in Excel

  - by thornomad

  I have an Access 2007 database that has a number of tables, some are fairly large (100,000+ records); I have created a union query to pull some of the same types of data from multiple tables into one large query for pivot table manipulation and reporting. For example: SELECT Language FROM Table1 UNION ALL SELECT Language FROM Table2 UNION ALL SELECT Language FROM Table3; This works. I found, quickly, however, that a union query will not show up when connecting to the datasource from Excel 2007. So, I created a second query to reference the union query. Like so: SELECT * FROM [The Above Union Query]; This query works and it, initially, was accessible from Excel. Time passed, I've added more data. Suddenly, when I connect to my Access database from Excel my query referencing the union has disappeared. MS Access shows no signs of an issue (data displays in Access) and my other non-union queries are showing up in Excel 2007 ... but not the one that references the union. What could be going on? Why did it disappear? I noticed if I switch some of the referenced tables in the union query to a smaller table (with less rows) all of sudden the query appears in Excel again. At least, I think that's what the difference is. I really can't put my finger on why some of the union queries won't show up and some will. Am stumped and need some guidance. Thanks.

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• What is the best way to remove flickering from a fast series of image loads in Flash?

  - by msandbot

  Hi, working on making a flash program that loads about 1000 jpegs and then plays them like a movie. Have all the buttons and stuff working but the time it takes for an image to load is so high that the movie can't be played at 30 fps. I've tried multiple ways of fixing this using 1 scrollpane and changing its source ever 30 ms. This one is the worst but simplest. Flickers cause strobing and it is unwatchable. used 2 scrollpanes that were duplicates of each other until I had to load. I would then make that one invisible, load it , then make it visible. Then load the background one. Works but same problem as the first at high speeds, just less severe. used 1 scrollpane per image . This works great, except that it fails miserably on any more than 100 of them due to the number of objects. Has anyone else experienced/solved/wants to help me solve this? None of my fixes have worked. Currently using action script 3, but will change if its not possible in that. Also, I want to be able to zoom in and then scroll around the window hence the scrollpanes, but if that's not possible its a sacrifice I'm willing to make

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• How to direct link to an attribute set?

  - by monocat

  I have created attributes; “Shop by Type” and “Shop by Color”. They work great within the layered navigation and extended search. I’ve designed graphics and placed them in the home page and would like to link to the respective attribute’s assigned products. Been searching the webs, but so far have been unsuccessful. If there’s no direct possible way, the next method would be creating cms pages and linking to it directly. How can I display products that are assigned to a specific attribute? Specifically “Multiple Select” types. I know you guys prefer at least some attempts, but as mentioned, been playing with it with no luck. I would appreciate some kind of starting point. Happy Holidays! Edit: I was able to put together this code that lists all the products assigned to said category id. Tried to filter it down where it only displays products that have an assigned same attribute with no luck yet. Any ideas? <?php $cat_id = 123; // category id $category = Mage::getModel('catalog/category')->load($cat_id); $_products = $category->getProductCollection() ->addAttributeToSelect('shop_by_color'); if (($this->getProductCollection()) && $_products->getSize()): ?> By the way, $cat_id is a sub category of root. Is there an easier way to point to it instead of using direct id number?

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• Providing downloads on ASP.net website

  - by Dave

  I need to provide downloads of large files (upwards of 2 GB) on an ASP.net website. It has been some time since I've done something like this (I've been in the thick-client world for awhile now), and was wondering on current best practices for this. Ideally, I would like: To be able to track download statistics: # of downloads is essential; actual bytes sent would be nice. To provide downloads in a way that "plays nice" with third-party download managers. Many of our users have unreliable internet connections, and being able to resume a download is a must. To allow multiple users to download the same file simultaneously. My download files are not security-sensitive, so providing a direct link ("right-click to download...") is a possibility. Is just providing a direct link sufficient, letting IIS handle it, and then using some log analyzer service (any recommendations?) to compile and report the statistics? Or do I need to intercept the download request, store some info in a database, then send a custom Response? Or is there an ASP.net user control (built-in or third party) that does this? I appreciate all suggestions.

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• Best practice on structuring asynchronous mailers (using Sidekiq)

  - by gbdev

  Just wondering what's the best way to go about structuring asynchronous mailers in my Rails app (using Sidekiq)? I have one ActionMailer class with multiple methods/emails... notifier.rb: class Notifier < ActionMailer::Base default from: "\"Company Name\" <[email protected]>" default_url_options[:host] = Rails.env.production? ? 'domain.com' : 'localhost:5000' def welcome_email(user) @user = user mail to: @user.email, subject: "Thanks for signing up!" end ... def password_reset(user) @user = user @edit_password_reset_url = edit_password_reset_url(user.perishable_token) mail to: @user.email, subject: "Password Reset" end end Then for example, the password_reset mail is sent in my User model by doing... user.rb: def deliver_password_reset_instructions! reset_perishable_token! NotifierWorker.perform_async(self) end notifier_worker.rb: class NotifierWorker include Sidekiq::Worker sidekiq_options queue: "mail" def perform(user) Notifier.password_reset(user).deliver end end So I guess I'm wondering a couple things here... Is it possible to define many "perform" actions in one single worker? By doing so I could keep things simple (one notifier/mail worker) as I have it and send many different emails through it. Or should I create many workers? One for each mailer (e.g. WelcomeEmailWorker, PasswordResetWorker, etc) and just assign them all to use the same "mail" queue with Sidekiq. I know it works as it is, but should I break out each of those mail methods (welcome_email, password_reset, etc) into individually mailer classes or is it ok to have them all under one class like Notifier? Really appreciate any advice here. Thanks!

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• Linq - reuse expression on child property

  - by user175528

  Not sure if what I am trying is possible or not, but I'd like to reuse a linq expression on an objects parent property. With the given classes: class Parent { int Id { get; set; } IList<Child> Children { get; set; } string Name { get; set; } } class Child{ int Id { get; set; } Parent Dad { get; set; } string Name { get; set; } } If i then have a helper Expression<Func<Parent,bool> ParentQuery() { Expression<Func<Parent,bool> q = p => p.Name=="foo"; } I then want to use this when querying data out for a child, along the lines of: using(var context=new Entities.Context) { var data=context.Child.Where(c => c.Name=="bar" && c.Dad.Where(ParentQuery)); } I know I can do that on child collections: using(var context=new Entities.Context) { var data=context.Parent.Where(p => p.Name=="foo" && p.Childen.Where(childQuery)); } but cant see any way to do this on a property that isnt a collection. This is just a simplified example, actually the ParentQuery will be more complex and I want to avoid having this repeated in multiple places as rather than just having 2 layers I'll have closer to 5 or 6, but all of them will need to reference the parent query to ensure security.

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• What hash algorithms are parallelizable? Optimizing the hashing of large files utilizing on multi-co

  - by DanO

  I'm interested in optimizing the hashing of some large files (optimizing wall clock time). The I/O has been optimized well enough already and the I/O device (local SSD) is only tapped at about 25% of capacity, while one of the CPU cores is completely maxed-out. I have more cores available, and in the future will likely have even more cores. So far I've only been able to tap into more cores if I happen to need multiple hashes of the same file, say an MD5 AND a SHA256 at the same time. I can use the same I/O stream to feed two or more hash algorithms, and I get the faster algorithms done for free (as far as wall clock time). As I understand most hash algorithms, each new bit changes the entire result, and it is inherently challenging/impossible to do in parallel. Are any of the mainstream hash algorithms parallelizable? Are there any non-mainstream hashes that are parallelizable (and that have at least a sample implementation available)? As future CPUs will trend toward more cores and a leveling off in clock speed, is there any way to improve the performance of file hashing? (other than liquid nitrogen cooled overclocking?) or is it inherently non-parallelizable?

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• How expensive is a context switch? Is it better to implement a manual task switch than to rely on OS

  - by Vilx-

  The title says it all. Imagine I have two (three, four, whatever) tasks that have to run in parallel. Now, the easy way to do this would be to create separate threads and forget about it. But on a plain old single-core CPU that would mean a lot of context switching - and we all know that context switching is big, bad, slow, and generally simply Evil. It should be avoided, right? On that note, if I'm writing the software from ground up anyway, I could go the extra mile and implement my own task-switching. Split each task in parts, save the state inbetween, and then switch among them within a single thread. Or, if I detect that there are multiple CPU cores, I could just give each task to a separate thread and all would be well. The second solution does have the advantage of adapting to the number of available CPU cores, but will the manual task-switch really be faster than the one in the OS core? Especially if I'm trying to make the whole thing generic with a TaskManager and an ITask, etc?

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• iPhone Development - CoreData runtime error

  - by Mustafa

  I'm facing a strange CoreData issue. Here's the log: 2010-04-07 15:59:36.913 MyProject[263:207] <MyEntity: 0x180370> (entity: MyEntity; id: 0x17e890 <x-coredata://0F55C533-41BD-4F09-9CCA-0CB304CAB065/MyEntity/p380> ; data: <fault>) 2010-04-07 15:59:36.918 MyProject[263:207] *** Terminating app due to uncaught exception 'NSObjectInaccessibleException', reason: 'The NSManagedObject with ID:0x17e890 <x-coredata://0F55C533-41BD-4F09-9CCA-0CB304CAB065/MyEntity/p380> has been invalidated.' I have a hierarchy of UITableViewControllers that use NSFetchedResultsController to populate the table, and when a particular row is selected, the detail view is shown. UITableView (MyMainEntity) UITableView (MyEntity) UITableView (MyEntity) detail view Both MyMainEntity UITableView and MyEntity UITableView use NSFetchedResultsController to show the records. Sometimes it crashes when i'm scrolling the tableView, and sometimes it crashes when i try to open the detail view. I can navigate to the MyEntity detail view multiple times before application crashes. What does this error mean? and how can i fix it!?

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• Identity alternative for SQL Azure Federation : are Azure Queues or Service Bus Queues a good choice?

  - by JYL

  As many of developers, I'm looking for a way to integrate my existing app to SQL Azure Federations, and replacing the Identity columns (the primary keys of my tables) is a big problem. For many reasons, I do NOT want use GUID for my primary keys (please don't open the debate about the GUID or not, it's not my question : i just don't want a GUID, period). So I need to build a key provider to replace the "identity" feature of a standard SQL database. I'm using Entity Framework, so i can easily find one place to set the Id value just before the insert (by overriding the SaveChanges method of my ObjectContext class). I just need to find a "not too complicated" implementation for getting the current Id, which is "farm-ready". I've read this SO post : "ID Generation for Sharded Database (Azure Federated Database)" and "Synchronizing Multiple Nodes in Windows Azure from MSDN Magazine", but this solution sounds a bit complicated for me. I'm thinking about creating (automatically) one azure queue for each SQL table, which contain a pre-loaded list of consecutive integer. When I want an Id value, I just have to get a message from the queue (which becomes invisible and is deleted on the way), which give me the current available Id. About the choice between "Windows Azure Queues" and "Windows Azure Service Bus Queues", I prefere "Windows Azure Queues", due to the "high" latency of Service Bus Queues. I don't think that the lack of "ordering garantee" of Azure Queues is a problem. What do you think about that idea of using Azure Queues to provide Id values ? Do you see any argument to give up that idea ? Do you have a better idea, or even a good practice, to provider integer ids in SQL Azure Federation databases ? Thanks.

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• Catch a PHP Object Instantiation Error

  - by Rob Wilkerson

  It's really irking me that PHP considers the failure to instantiate an object a Fatal Error (which can't be caught) for the application as a whole. I have set of classes that aren't strictly necessary for my application to function--they're really a convenience. I have a factory object that attempts to instantiate the class variant that's indicated in a config file. This mechanism is being deployed for message storage and will support multiple store types: DatabaseMessageStore FileMessageStore MemcachedMessageStore etc. A MessageStoreFactory class will read the application's preference from a config file, instantiate and return an instance of the appropriate class. It might be easy enough to slap a conditional around the instantiation to ensure that class_exists(), but MemcachedMessageStore extends PHP's Memcached class. As a result, the class_exists() test will succeed--though instantiation will fail--if the memcached bindings for PHP aren't installed. Is there any other way to test whether a class can be instantiated properly? If it can't, all I need to do is tell the user which features won't be available to them, but let them continue one with the application. Thanks.

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• Advice: Python Framework Server/Worker Queue management (not Website)

  - by Muppet Geoff

  I am looking for some advice/opinions of which Python Framework to use in an implementation of multiple 'Worker' PCs co-ordinated from a central Queue Manager. For completeness, the 'Worker' PCs will be running Audio Conversion routines (which I do not need advice on, and have standalone code that works). The Audio conversion takes a long time, and I need to co-ordinate an arbitrary number of the 'Workers' from a central location, handing them conversion tasks (such as where to get the source files, or where to ask for the job configuration) with them reporting back some additional info, such as the runtime of the converted audio etc. At present, I have a script that makes a webservice call to get the 'configuration' for a conversion task, based on source files located on the worker already (we manually copy the source files to the worker, and that triggers a conversion routine). I want to change this, so that we can distribute conversion tasks ("Oy you, process this: xxx") based on availability, and in an ideal world, based on pending tasks too. There is a chance that Workers can go offline mid-conversion (but this is not likely). All the workers are Windows based, the co-ordinator can be WIndows or Linux. I have (in my initial searches) come across the following - and I know that some are cross-dependent: Celery (with RabbitMQ) Twisted Django Using a framework, rather than home-brewing, seems to make more sense to me right now. I have a limited timeframe in which to develop this functional extension. An additional consideration would be using a Framework that is compatible with PyQT/PySide so that I can write a simple UI to display Queue status etc. I appreciate that the specifics above are a little vague, and I hope that someone can offer me a pointer or two. Again: I am looking for general advice on which Python framework to investigate further, for developing a Server/Worker 'Queue management' solution, for non-web activities (this is why DJango didn't seem the right fit).

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• Trying to edit an entity with data from dropdowns in MVC...

  - by user598352

  Hello! I'm having trouble getting my head around sending multiple models to a view in mvc. My problem is the following. Using EF4 I have a table with attributes organised by category. Couldn't post an image :-( [Have a table called attributes (AttributeTitle, AttributeName, CategoryID) connected to a table called Category (CategoryTitle).] What I want to do is be able to edit an attribute entity and have a dropdown of categories to choose from. I tried to make a custom viewmodel public class AttributeViewModel { public AttributeViewModel() { } public Attribute Attribute { get; set; } public IQueryable<Category> AllCategories { get; set; } } But it just ended up being a mess. <div class="editor-field"> <%: Html.DropDownList("Category", new SelectList((IEnumerable)Model.AllCategories, "CategoryID", "CategoryName")) %> </div> I was getting it back to the controller... [HttpPost] public ActionResult Edit(int AttributeID, FormCollection formcollection) { var _attribute = ProfileDB.GetAttribute(AttributeID); int _selcategory = Convert.ToInt32(formcollection["Category"]); _attribute.CategoryID = (int)_selcategory; try { UpdateModel(_attribute); (<---Error here) ProfileDB.SaveChanges(); return RedirectToAction("Index"); } catch (Exception e) { return View(_attribute); } } I've debugged the code and my _attribute looks correct and _attribute.CategoryID = (int)_selcategory updates the model, but then I get the error. Somewhere here I thought that there should be a cleaner way to do this, and that if I could only send two models to the view instead of having to make a custom viewmodel. To sum it up: I want to edit my attribute and have a dropdown of all of the available categories. Any help much appreciated!

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• Haskell quiz: a simple function

  - by levy

  I'm not a Haskell programmer, but I'm curious about the following questions. Informal function specification: Let MapProduct be a function that takes a function called F and multiple lists. It returns a list containing the results of calling F with one argument from each list in each possible combination. Example: Call MapProduct with F being a function that simply returns a list of its arguments, and two lists. One of the lists contains the integers 1 and 2, the other one contains the strings "a" and "b". It should return a list that contains the lists: 1 and "a", 1 and "b", 2 and "a", 2 and "b". Questions: How is MapProduct implemented? What is the function's type? What is F's type? Can one guess what the function does just by looking at its type? Can you handle inhomogeneous lists as input? (e.g. 1 and "a" in one of the input lists) What extra limitation (if any) do you need to introduce to implement MapProduct?

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