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• Postgres : Post statement (or insert) asynchronous, non-blocking processing.

  - by Hassan Syed

  I'm wondering if it is possible, that after a collection of rows is inserted, to initiate an operation that is executed asynchronously, is non-blocking, and doesn't need to inform the originator of the request - of the result. I am working with large amounts of events and I can guarantee that the post-insert logic will not fail -- I just want to have a single insert thread in my event-sources, and I want this thread to keep flying without blocking, and without being responsible for any post-delivery book-keeping. I can tell you that I would potentially have a 100 of these jobs executing concurrently and each job might operate on 5 tables with anywhere between 200-1000 inserts on each of these tables. A hint in the right direction should be enough.

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• django related_name for field clashes.

  - by Absolute0

  I am getting a field clash in my models: class Visit(models.Model): user = models.ForeignKey(User) visitor = models.ForeignKey(User) Error: One or more models did not validate: profiles.visit: Accessor for field 'user' clashes with related field 'User.visit_set'. Add a related_name argument to the definition for 'user'. profiles.visit: Accessor for field 'visitor' clashes with related field 'User.visit_set'. Add a related_name argument to the definition for 'visitor'. what would be a sensible 'related_field' to use on visitor field? This model basically represents the visits that take place to a particular user's profile. Also should I replace any of the ForeignKey's with a ManyToManyField? The logic is a bit confusing. Edit: This seems to fix it, but I am unsure if its what I want. :) class Visit(models.Model): user = models.ForeignKey(User) visitor = models.ForeignKey(User, related_name='visitors')

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• Basic Conditional Checking for IF statements in C

  - by ZaZu

  Hi there, Can someone please explain what really goes on in this code ? If I put the AND statement, the message wont show if values are less than 0 or greater than 10 ... I think I must use 1 0 logic to work this out right ? I just need someone to briefly explain it please. #include<stdio.h> main(){ puts("enter number"); scanf("%d",num); if(num<0 || num >10) puts("yay"); } How is that IF statement different when AND is put : #include<stdio.h> main(){ puts("enter number"); scanf("%d",num); if(num<0 && num >10) puts("yay"); } Thanks !!

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• How do I measure distances in an image?

  - by Ram Bhat

  Let's say we have an image like so Let's say we've already used filters and an edge detection algorithm in this pic. Now my goal is to measure distances (NOT actual distances, distance can be in any arbitrary unit) . eg: How do I find the length of the hall? (until the window) Or the height of the bookshelves? How exactly do you place the "scale" and measure. I'm looking for ideas. However it would help if the answers were in terms of OpenCV.

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• Model-layer validation in Doctrine, Symfony

  - by Andree

  Hi there, I have a schema.yml containing something similiar to the following: Character: tableName: characters actAs: { Timestampable: ~ } columns: id: { type: integer(4), primary: true, autoincrement: true } name: { type: string(255), notnull: true, notblank: true, minlength: 3 } I define the minlength of the column name to be 3. I created a unit test to test the minlength validation, and I found out that the validation is not working. $character = new Character(); $character->set('name', 'Dw'); $t->ok(! $character->isValid()); # This test failed Can someone tell me what might be the problem here? Thanks, Andree

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• Combining features from other projects in an ASP.NET MVC application

  - by Katie D

  Hello, I am writing an ASP.NET MVC application that combines a set of features from existing applications. The new application is suppose to use UI features and logic created (especially for this purpose) in the existing applications. For that reason I wanted to create in the existing applications some kind of a "blackbox" that I will be able to drop in my new application along with a matching connection string, and it will work independently, binding data on it's own. I thought about using partial views, but I am having trouble with passing the model data to it, since the controller of the new application should not know about the model of the existing applications. I can not use ASP.NET WebForms, since my application should be a "postback-less" application, and ASP.NET AJAX toolkit or frameworks alike are out of the question. Any help would be greatly appreciated. Thank you, Katie

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• For what programs are Objective C and Ruby ideal on the Mac?

  - by Kurt

  Hi, as a Mac outsider it seems that two popular programming languages on the Mac appear to be Objective C and Ruby. From what I understand the main API Cocoa seems to be written in and optimized for Objective C, but it is also possible to use Ruby for that. Are there different areas where each language is ideal, for example, I could imagine Objective C could be ideal for a GUI layer, or standalone desktop app, and Ruby could be good for web services etc. What about classic business logic, or data access layers? What language would be a good choice for a library of services for example? Can we write a library in one language and link to it from a main program written in the other language? If I wanted to write a layered enterprise application using domain driven design and dependency injection which languages could support each concerns? Are things like DDD and DI common amongst Mac devs? Just a curious outsider.

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• slow php command line performance - is this normal or do I have an install problem?

  - by Frank Schwieterman

  I have a simple PHP app that prints 'hello world'. When I run it from the command line it takes 6 seconds. Is this normal? It seems to take 1 seconds before "hello world" prints, then 5 seconds after. I assume this is overhead of the interpreter. I am running PHP version 5.2.12 on Windows Server 2008 R2. Could this be an install issue, or is it typical? I did a manual install of PHP then added whatever components were needed to run Drupal. The only PHP addon I remember adding was MDB2, CGI support is there too. I am used to a Lua project I run from the command line, hundreds of lines of code that will run in under a second. I have some unit tests I run from the command line, and already with just a few they are very slow. I run them from Netbeans and the tests are still very slow.

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• Style of if: to nest or not to nest

  - by Marco

  A colleague of mine and me had a discussion about the following best-practice issue. Most functions/methods start with some parameter checking. I advocate the following style, which avoids nesting. if (parameter one is ugly) return ERROR; if (parameter two is nonsense || it is raining) return ERROR; // do the useful stuff return result; He, who comes from a more functional/logic programming background, prefers the following, because it reduces the number of exit points from the function. if (parameter one is ok) { if (parameter two is ok && the sun is shining) { // do the useful stuff return result } } return ERROR; Which one would you prefer and why?

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• How to send reminder notifications to subscribers for renewal from SQL Server 2005?

  - by codemonkie

  I have a table in SQL DB, namely dbo.subscribers, it contains following columns: -SubscriberID -JoinDateTime The business logic says a subscription last for 2 weeks and a reminder should be sent after 7 days from the JoinDateTime. The way that the system was designed to send reminders are via a URL call, e.g. http://xxx.xxx.xxx.xxx/renew_userid=SubscriberID/ and that can only be called from our webserver which is the only whitelisted IP machines given. Currently there is a windows service written to query the DB once a day at midnight to grab all expiring subscribers and send them reminders, however this batch approach only sends reminders to the nearest date, well, I could have set the interval down from 1 day to 1 hour such that the service can send notifications out closer to the exact JoinDateTime + 7 days requirements. I have heard a stored procedure can be written and perform task like this to a nearly real-time manner, if yes, please give me some hints on how to do it. Another question is - is SSRS bit of an overkill to perform things like this? Please advice. TIA

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• How to join nearly identical several queries into one?

  - by Devyn

  Hi, Assume I have an order_dummy table where order_dummy_id, order_id, user_id, book_id, author_id are stored. You may complain the logic of my table but I somehow need to do it that way. I want to execute following queries. SELECT * FROM order_dummy WHERE order_id = 1 AND user_id = 1 AND book_id = 1 ORDER BY `order_dummy_id` DESC LIMIT 1 SELECT * FROM order_dummy WHERE order_id = 1 AND user_id = 1 AND book_id = 2 ORDER BY `order_dummy_id` DESC LIMIT 1 SELECT * FROM order_dummy WHERE order_id = 1 AND user_id = 1 AND book_id = 3 ORDER BY `order_dummy_id` DESC LIMIT 1 Please keep in mind that several numbers of same book is included in one order. Therefore, I list order_dummy_id by descending and limit 1 so only LATEST ORDER of A BOOK is shown. But my goal is to show other books in that way in one table. I used group by like this ... SELECT * FROM order_dummy WHERE order_id = 1 AND user_id = 1 GROUP BY book_id but it only shows order_dummy_id with ascending result. I have no idea anymore. Looking forward your kindness help!

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• long running process in asp.net C#

  - by user339323

  Hello All, I have a web application that has a long running (resource intensive) process in the code behind and the end output is a pdf file (images to pdf conversion tool) It runs fine..and since I am on a dedicated server, it is not at all a problem with respect to resources right now. However, I wonder that the system would reach its resource limits if, there are more than 20 users processing at a time. I have seen services online where the user enters their email and the processes are, I suppose, queued in the background and the results emailed with the 1st in 1st out method. Can someone please give me a start on how to implement this kind of logic in asp.net applications using C#? Thanks a lot in advance, Prasad.

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• Proper abstraction of the database tier in a 3 tier system?

  - by Earlz

  Hello, I am creating a 3 tier application. Basically it goes Client - (through optional server to be a thin-client) - Business Logic - Database Layer And basically making it so that there is never any skipping around. As such, I want for all of the SQL queries and such to be in the Database Layer. Well, now I'm a bit confused. I made a few static classes to start off the database tier but what should I do for the database connections? Should I just create a new database connection anytime I enter the Database Layer or would that be wasteful? Does Connection.Open() take time whenever you have a ConnectionPool? To me, it just feels wrong for the Business tier to have to pass in a IdbConnection object to the Database tier. It seems like the Database tier should handle all of that DB-specific code. What do you think? How can I do it the proper way while staying practical?

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• Is there a free code coverage tool suitable for use with .NET 4 and NUnit?

  - by Damian Powell

  Is there a free code coverage tool suitable for use with .NET 4 and NUnit that runs from the command line (and is thus suitable for use on a build server)? Please note that any tools that require editions of Visual Studio higher than Professional are not appropriate in this case. I am asking this question because I can't get NCover 1.5.8 to work with NUnit 2.5.5 on a .NET 4 C# app. I can run the unit tests, and I can generate a Coverage.Xml file, but it is empty - it contains no sequence points. After a lot of research, I have concluded that this is because NCover 1.5.8 simply doesn't work with .NET 4. However, if you know better, please feel free to answer this question from another user.

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• Django complex queries

  - by Josh K

  I need to craft a filter for an object that checks date ranges. Right now I'm performing a very inefficient loop which checks all the objects. I would like to simplify this to a database call. The logic is you have a start and an end date objects. I need to check if the start OR the end is within the range of an appointment. if (start >= appointment.start && start < appointment.end) || (end > appointment.start && end <= appointment.end) I could do this in SQL, but I'm not as familiar with the Django model structure for more complex queries.

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• Trouble rendering a view inside a generic class

  - by Horace Loeb

  I'm trying to encapsulate the logic for generating my sitemap in a separate class so I can use Delayed::Job to generate it out of band: class ViewCacher include ActionController::UrlWriter def initialize @av = ActionView::Base.new(Rails::Configuration.new.view_path) @av.class_eval do include ApplicationHelper end end def cache_sitemap songs = Song.all sitemap = @av.render 'sitemap/sitemap', :songs => songs Rails.cache.write('sitemap', sitemap) end end But whenever I try ViewCacher.new.cache_sitemap I get this error: ActionView::TemplateError: ActionView::TemplateError (You have a nil object when you didn't expect it! The error occurred while evaluating nil.url_for) on line #5 of app/views/sitemap/_sitemap.builder: I assume this means that ActionController::UrlWriter is not included in the right place, but I really don't know

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• Performance Overhead of Perf Event Subsystem in Linux Kernel

  - by Bo Xiao

  Performance counters for Linux are a new kernel-based subsystem that provide a framework for all things performance analysis. It covers hardware level (CPU/PMU, Performance Monitoring Unit) features and software features (software counters, tracepoints) as well. Since 2.6.33, the kernel provide 'perf_event_create_kernel_counter' kernel api for developers to create kernel counter to collect system runtime information. What I concern most is the performance impact on overall system when tracepoint/ftrace is enabled. There are no docs I can find about them. I was once told that ftrace was implemented by dynamically patching code, will it slow the system dramatically?

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• Better method for flipping multidimensional array?

  - by sudowned

  I've retrieved some data from the database, which is in the following structure: [0] [item_id] = 197 [dice_chat_css] = "foo" [dice_image] = "bar.png" [1] [item_id] = 128 [dice_chat_css] = "foo" [dice_image] = "bar.png" The most convenient and computationally inexpensive way for me to pass this data to the rest of my (PHP) application is with item_id as the index, because it saves having to loop over the array to look up values. If this was a flat array, I could accomplish this trivially with array_flip, but since it isn't, it's my pick of using either the multidimensional array_flip listed in the comments on PHP.net, or roll my own logic: for ($i = 0; $i < sizeOf($r); $i++){ $s[$r[$i]['item_id']]['dice_image'] = $r[$i]['dice_image']; $s[$r[$i]['item_id']]['dice_chat_css'] = $r[$i]['dice_chat_css']; } I know it's simple, but it feels like I'm reinventing the wheel here. Is there an accepted, more optimized method available or am I being weird about this?

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• Should class IOException in Java have been an unchecked RuntimeException?

  - by Derek Mahar

  Do you agree that the designers of Java class java.io.IOException should have made it an unchecked run-time exception derived from java.lang.RuntimeException instead of a checked exception derived only from java.lang.Exception? I think that class IOException should have been an unchecked exception because there is little that an application can do to resolve problems like file system errors. However, in When You Can't Throw An Exception, Elliotte Rusty Harold claims that most I/O errors are transient and so you can retry an I/O operation several times before giving up: For instance, an IOComparator might not take an I/O error lying down, but — because many I/O problems are transient — you can retry a few times, as shown in Listing 7: Is this generally the case? Can a Java application correct I/O errors or wait for the system to recover? If so, then it is reasonable for IOException to be checked, but if it is not the case, then IOException should be unchecked so that business logic can delegate handling of this exception to a separate system error handler.

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• How to handle all unhandled exceptions when using Task Parallel Library?

  - by Buu Nguyen

  I'm using the TPL (Task Parallel Library) in .NET 4.0. I want to be able to centralize the handling logic of all unhandled exceptions by using the Thread.GetDomain().UnhandledException event. However, in my application, the event is never fired for threads started with TPL code, e.g. Task.Factory.StartNew(...). The event is indeed fired if I use something like new Thread(threadStart).Start(). This MSDN article suggests to use Task#Wait() to catch the AggregateException when working with TPL, but that is not I want because it is not "centralized" enough a mechanism. Does anyone experience same problem at all or is it just me? Do you have any solution for this?

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• Using the .where method in Rails3

  - by Elliot

  Hey Guys, I've just started using the .where method, and I'm a little bit confused about how to fully utilize it. I'd like to do something like: @books = Book.where(:author_id => 1 || 2) clearly I know that doesn't work, but I'm trying to demonstrate that I want some extra logic here. some "or" "and" "does not equal" etc. Any ideas for where I can research this? I was looking in the rails API but I didnt see anything that was that helpful. Thanks!

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• How can I use MVC ideas without using classes?

  - by jpjp

  As of right now, I am still shaky on classes, so I don't want to use any classes for my site. I'm still practicing with classes. But how can I implement the MVC idea without classes? Would this work for a MVC? index.php (the view) index_controller.php index_model.php Is this right for what a MVC should be? View: show html, css, forms Controller: get $_POST from forms and any data from the user, get info from db Model: do all the functions, insert/delete in db, etc Basically separate the HTML/css for the view, all the data collecting for the controller, and the logic for the model. And just connect them all using require_once.

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• Use where condition with unjoined table

  - by Dragos D

  I have the following problem: I am trying to retreive a sum value based on one condition. Problem is that I can't join the conditional value since my tables aren't joined. Here is my syntax: SELECT SUM(value) FROM value v join day d on v.day_id = d.day_id join budget b on d.budget_id = b.budget_id join unit u on v.unit_id = u.unit_id where #output.class = (SELECT distinct s.class FROM sale s where s.id = #output.sale_id) AND u.unit_name in ('electronics') With this sybtax I get no error but neither values. Can you please tell me where I do wrong?

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• Oracle SQL Update query takes days to update

  - by B Senthil Kumar

  I am trying to update a record in the target table based on the record coming in from source. For instance, if the incoming record is present in the target table I would update them in the target else I would simply insert. I have over one million records in my source while my target has 46 million records. The target table is partitioned based on calendar key. I implement this whole logic using Informatica. I find that the Informatica code is perfectly fine looking at the Informatica session log but its in the update it takes long time (more than 5 days to update one million records). Any suggestions as to what can be done on the scenario to improve the performance?

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• Should I create subclass NSManagedObject or not?

  - by TP

  Hi, I have spent a few days learning and writing NSCoding and finally got it working. However, it took very long to archive and unarchive the (quite complex) object graph, which is unacceptable. After searching the internet for some time, I think the better way is to use core data. Do you recommend that 1) I should rewrite all my classes as subclasses of NSManagedObject or 2) should I create an instance variable of NSManagedObject in each of my class so that any changes to the class also updates its core data representation? Doing either way will need significant changes to the exiting classes and I think I have to update lots of unit test cases as well if it changes the way the classes are initialized. What do you recommend? I really don't want to head to the wrong approach again... Thanks!

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