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• Ruby on Rails: building a model with an attribute not in the database?

  - by randombits

  I have a model that sets one of its attributes based off of a form parameter that a user submits. The model is a child resource to a parent resource Home. A hypothetical example is the following: A class Person has an age attribute. The user submits a birthdate as an HTTP POST parameter and from that, I need to derive the age of the user. So I'd do something like this: @home.people.build(:name => params[:name], :birthdate => params[:birthdate]) Rails would barf on that for obvious reasons, complaining it doesn't know what the attribute birthdate is. What's the proper way of going about this? Is it possible to use the build constructor with the supplied solution so that my foreign key relations are also setup properly? If not, what's a better way to work around this problem?

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• Filter across three tables using Django

  - by Vanessa MacDougal

  I have 3 django models, where the first has a foreign key to the second, and the second has a foreign key to the third. Like this: class Book(models.Model): year_published = models.IntField() author = models.ForeignKey(Author) class Author(models.Model): author_id = models.AutoField(primary_key=True) name = models.CharField(max_length=50) agent = models.ForeignKey(LitAgent) class LitAgent(models.Model): agent_id = models.AutoField(primary_key=True) name = models.CharField(max_length=50) I want to ask for all the literary agents whose authors had books published in 2006, for example. How can I do this in Django? I have looked at the documentation about filters and QuerySets, and don't see an obvious way. Thanks.

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• Should I use implicit conversions to enforce preconditions?

  - by Malvolio

  It occurs to me that I could use use implicit conversions to both announce and enforce preconditions. Consider this: object NonNegativeDouble { implicit def int2nnd(d : Double) : NonNegativeDouble = new NonNegativeDouble(d) implicit def nnd2int(d : NonNegativeDouble) : Double = d.v def sqrt(n : NonNegativeDouble) : NonNegativeDouble = scala.math.sqrt(n) } class NonNegativeDouble(val v : Double ) { if (v < 0) { throw new IllegalArgumentException("negative value") } } object Test { def t1 = { val d : Double = NonNegativeDouble.sqrt(3.0); printf("%f\n", d); val n : Double = NonNegativeDouble.sqrt(-3.0); } } Ignore for the moment the actual vacuity of the example: my point is, the subclass NonNegativeDouble expresses the notion that a function only takes a subset of the entire range of the class's values. First is this: A good idea, a bad idea, or an obvious idea everybody else already knows about Second, this would be most useful with basic types, like Int and String. Those classes are final, of course, so is there a good way to not only use the restricted type in functions (that's what the second implicit is for) but also delegate to all methods on the underlying value (short of hand-implementing every delegation)?

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• Windows 7 UAC elevation

  - by Goz

  I have a single thread that I'd like to run as an administrator in my application. The rest of the application I can happily run as the default user level (asInvoker). Is this possible? I notice there is an "ImpersonateLoggedOnUser" function. Can I somehow use this to log the administrator on and then get the thread to impersonate that person? It seems as though this ought to be something pretty trivial to do ... but there doesn't appear to be any obvious way to do it. Can anyone help me out?

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• Starting out with vote_fu

  - by zizee

  Hi All, Trying my luck with the vote_fu rails plugin. The functionality looks like exactly what I need for a project of mine, but I have hit a roadblock. I have followed the github readme to the letter, installing it as a plugin. I have put acts_as_voteable on my "Event" model and acts_as_voter on my User model. In the console, when I try: >> event.votes or >> user.votes it successfully returns an empty array. but when I try to do the following: user.vote_for(event) I get "NoMethodError: undefined method `user_id' for #<Vote:0x7f5ed4355540>" Any ideas? I'm probably just missing something obvious, but maybe something is missing from the plugin's readme. Thanks.

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• Combining DROP USER and DROP DATABASE with SELECT .. WHERE query?

  - by zsero

  I'd like to make a very simple thing, replicate the functionality of mysql's interactive mysql_secure_installation script. My question is that is there a simple, built-in way in MySQL to combine the output of a SELECT query with the input of a DROP user or DROP database script? For example, if I'd like to drop all users with empty passwords. How could I do that with DROP USER statement? I know an obvious solution would be to run everything for example from a Python script, run a query with mysql -Bse "select..." parse the output with some program construct the drop query run it. Is there an easy way to do it in a simple SQL query? I've seen some example here, but I wouldn't call it simple: http://stackoverflow.com/a/12097567/518169 Would you recommend making a combined query, or just to parse the output using for example Python or bash scripts/sed?

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• Mac OSX: Passing a link to file from user process to kernel module.

  - by Inso Reiges

  Hello, I need to pass a link to file from a user process to the OSX kernel driver. By link i mean anything that uniquely identifies a file on the local filesystem. I need that link to do I/O on that file in kernel. The most obvious solution seems to pass a file name and use a VFS vnode lookup. However i noticed, that Apple Disk Images helper process passes a raw data array for image-path property to driver when attaching a disk image file: <2f 56 6f 6c 75 6d 65 73 2f 73 74 6f 72 61 67 65 2f 74 65 73 74 32 2e 64 6d 67> What is that diskimages-helper passes to the kernel driver? Some serialized type perhaps? If yes, what type is it and how can i use it?

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• How can I check if an order with a given increment id already exists in magento?

  - by Thomas Vander Stichele

  I am new to Magento. What's the proper way to check if an order with a given increment id already exists ? The obvious way: $order = Mage::getModel('sales/order')->loadByIncrementId($reservedOrderId); if ($order) { Mage::log('already have order with id ' . $reservedOrderId); return $order; } does not work, because I get a new and empty model instance back. What's the correct way in magento to see if I have no such model for that id ?

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• Advantages of using a Dynamic Client with JAX-WS

  - by jconlin

  What are the advantages of using a dynamic client with JAX-WS services as opposed to just using generated client classes? What are the disadvantages? **For my particular case I am using Apache CXF, I'm not sure what other libraries allow "dynamic" clients. -I thought I didn't need to add this, but... I'm looking for non-obvious(I know...subjective) advantages. I don't need someone else to tell me that an advantage of not using generated classes is that I don't need to generate classes.

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• New/strange Java "try()" syntax?

  - by Ali

  While messing around with the custom formatting options in Eclipse, in one of the sample pieces of code, I say code as follows: /** * 'try-with-resources' */ class Example { void foo() { try (FileReader reader1 = new FileReader("file1"); FileReader reader2 = new FileReader("file2")) { } } } I've never seen try used like this and I've been coding in Java for 9 years! Does any one know why you would do this? What is a possible use-case / benefit of doing this? An other pieces of code I saw, I thought was a very useful shorthand so I'm sharing it here as well, it's pretty obvious what it does: /** * 'multi-catch' */ class Example { void foo() { try { } catch (IllegalArgumentException | NullPointerException | ClassCastException e) { e.printStackTrace(); } } }

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• Implicit declaration when using a function before it is defined in C, why can't the compiler figure this out?

  - by rolls

  As the title says, I know what causes this error but I want to know why the compiler gives it in this circumstance. Eg : main.c void test(){ test1(); } void test1(){ ... } Would give an implicit declaration warning as the compiler would reach the call to test1() before it has read its declaration, I can see the obvious problems with this (not knowing return type etc), but why can't the compiler do a simple pass to get all function declarations, then compile the code removing these errors? It just seems so simple to do and I don't believe I've seen similar warnings in other languages. Does anyone know if there is a specific purpose for this warning in this situation that I am overlooking?

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• Declaring a prototype of type "struct" - C

  - by Jamie Keeling

  I've been racking my brains on this for a while, I'm simply trying to create a method that returns a struct as I wish to return two int's. My prototype for the method is as follows: typedef struct RollDice(); Also the method itself: typedef struct RollDice() { diceData diceRoll; diceRoll.dice1 = 0; diceRoll.dice2 = 0; return diceRoll; } The compiler shows the error: "Syntax error: ')'" for both the prototype and actual method. The struct itself: typedef struct { int dice1; int dice2; }diceData; Is it obvious where I'm going wrong? I've tried everything I can think of. Thanks

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• Managing StringBuilder Resources in C#

  - by Jim Fell

  Hello. My C# (.NET 2.0) application has a StringBuilder variable with a capacity of 2.5MB. Obviously, I do not want to copy such a large buffer to a larger buffer space every time it fills. By that point, there is so much data in the buffer anyways, removing the older data is a viable option. Can anyone see any obvious problems with how I'm doing this (i.e. am I introducing more performance problems than I'm solving), or does it look okay? tText_c = new StringBuilder(2500000, 2500000); private void AppendToText(string text) { if (tText_c.Length * 100 / tText_c.Capacity > 95) { tText_c.Remove(0, tText_c.Length / 2); } tText_c.Append(text); } Thanks.

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• VB.NET: Force user to use the topmost form

  - by SiliconCelery

  I'm programming a Minesweeper clone in Visual Studio 2010, with VB.NET, as a Windows Form Application, and I'm having trouble with the Game Won and Game Lost forms. When I show those forms, I want the game form to still be visible, so that the player can see where the mines were, but I don't want the game form to be enabled until the Game Won or Game Lost form is closed. Exactly like Windows Minesweeper does when you win or lose. There aren't any obvious properties for this, as far as I can see, and I've had no luck Googling, I don't know what terms to search. Any help is appreciated, thanks.

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• Is there a way to load an icon from a memory file handler?

  - by Jon Trauntvein

  I am writing wxWidgets application where I am importing the .ICO file as a header. I am attempting to use a wxMemoryFSHandler to make this icon (and others as well) accessible as files. I am using the following code to do this: wxFileSystem::AddHandler(new wxMemoryFSHandler); wxMemoryFSHandler::AddFileWithMimeType( "app_inactive.ico", CsiWebAdmin_ico, sizeof(CsiWebAdmin_ico), "image/vnd.microsoft.icon"); Unfortunately, if I try to load an icon from this "file" as shown below, it does not work. As I stepped through the MSW source (wx 2.8.10), I can see that the loader never attempted to resolve the virtual file name. wxIcon icon("memory:app_inactive.ico"); I have also tried the following: wxIcon icon(wxIconLocation("memory:app_inactive.ico")); and have encountered the same results. I realise that I can use resources to load these files but I would still face the same dilemma when the time came to port my application to GTK. Is there something obvious that I am missing?

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• AsyncTask Threading Rule - Can it really only be used once?

  - by stormin986

  In the documentation on AsyncTask it gives the following as a rule related to threading: The task can be executed only once (an exception will be thrown if a second execution is attempted.) All this means is that you have to create a new instance of the class every time you want to use it, right? In other words, it must be done like this: new DownloadFilesTask().execute(url1, url2, url3); new DownloadFilesTask().execute(url4, url5, url6); Or conversely, you can NOT do the following: DownloadFilesTask dfTask = new DownloadFilesTask(); dfTask().execute(url1, url2, url3); dfTask().execute(url4, url5, url6); Can someone verify this is an accurate interpretation? I realize I pretty much just answered this for myself as I was typing this out... But it wasn't immediately obvious to me so I think this would be useful to have posted nonetheless.

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• iPhone - Make loadView entries fill up parent view?

  - by Eli

  I have a loadView call that basically places one view at the top (like a header) and one at the bottom (like a footer). It's possible via a passed in parameter to not have a header or a footer, to hide them later, or to resize the view. I have all this working, but it's very susceptible to breaking because the views can go in various places of various sizes and all must be manually set to the correct size or they will not use up all the space. I want one in between the two of them that automatically resizes to fill whatever space is not taken by the others. loadView doesn't seem to be able to obtain the size of its parent's frame (or where it's being fit in, exactly), nor do I see an obvious way to just put the center view at a certain position and have its width and height automatically adapted. Any ideas? If I'm not explaining myself well enough and you know Java Swing, think BorderLayout with a BorderLayout.NORTH, BorderLayout.SOUTH, and BorderLayout.CENTER component.

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• Efficient most common suffix algorithm?

  - by taw

  I have a few GBs worth of strings, and for every prefix I want to find 10 most common suffixes. Is there an efficient algorithm for that? An obvious solution would be: Store sorted list of <string, count> pairs. Identify by binary search extent for prefix we're searching. Find 10 highest counts in this extent. Possibly precompute it for all short prefixes, so it doesn't ever need to look at large portion of data. I'm not sure if that would actually be efficient at all. Is there a better way I overlooked? Answers must be real time, but it can take as much preprocessing as necessary.

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• Bash variable kills script execution

  - by Kyle Terry

  Sorry if this is better suited at serverfault, but I think it learns more towards the programming side of things. I have some code that's going into /etc/rc.local to detect what type of touch screen monitor is plugged in and changes out the xorg.conf before launching X. Here is a small snippet: CURRENT_MONITOR=`ls /dev/usb | grep 'egalax_touch\|quanta_touch'` case $CURRENT_MONITOR in '') CURRENT_MONITOR='none' ;; esac If one of those two touch screens is plugged in, it works just fine. If any other monitor is plugged in, it stops at the "CURRENT_MONITOR=ls /dev/usb | grep 'egalax_touch\|quanta_touch'." For testing I touched two files. One before creating CURRENT_MONITOR and one after CURRENT_MONITOR and only file touched before is created. I'm not a bash programmer so this might be something very obvious.

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• Can you create a HIPAA compliant Amazon S3 Web Application?

  - by xkingpin

  I am facing some questions when trying to design an S3 application using ASP.NET MVC and trying to stay HIPAA compliant. My initial plan was to require an SSL connection to my web server, encrypt the images on my server, then send them to s3 using my private keys. Here's my obvious concerns: You cannot store unencrypted images in any temporary file cache when client views images within the browser. Even if I setup an ashx to generically handle the image in memory, couldn't this get stored in cache? Saying the images will be encrpyted because you will be connecting to my server via https still does not guarantee all browsers will not cache data. It's not possible to even consider the "Query String" with expiration option since data will be encrypted before being stored on disk at s3, and will again be decrypted at my server in memory. I think my only option would be to write/purchase some sort of ActiveX component that will not expose the image as a simple html image source or write my app as a client side WinForm application.

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• Designing constructors around type erasure in Java

  - by Internet Friend

  Yesterday, I was designing a Java class which I wanted to be initalized with Lists of various generic types: TheClass(List<String> list) { ... } TheClass(List<OtherType> list) { ... } This will not compile, as the constructors have the same erasure. I just went with factory methods differentiated by their names instead: public static TheClass createWithStrings(List<String> list) public static TheClass createWithOtherTypes(List<OtherType> list) This is less than optimal, as there isn't a single obvious location where all the different options for creating instances are available. I tried to search for better design ideas, but found surprisingly few results. What other patterns exist for designing around this problem?

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• Releasing WinForm Program Updates

  - by Tinkerer_CardTracker

  Hello, Another quick question. I'd like to release some updates for a WinForm program, but to date I have simply released an all-new compile. People have to un-install the old version and install the new version. I bet there's a way to get around this, but I don't know what it's called. As you may guess, searches for "updates" "new version" "install" and the other obvious things I've tried have generated an impressive number of irrelevant results. _< I suspect this process has a particular name, which should point me in the right direction, but if it doesn't please link to a tutorial or something. Thanks again, this site is great! :)

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• Netbeans PHP require_once() problem

  - by mawg

  I'm stumped! In PHP in Netbeans (6.8), a project has two files, file1.php and file2.php file1.php starts require_once('file2.php'); and I get Warning: require_once(query_form.php): failed to open stream: No such file or directory in C:\xampp\htdocs\my_project\file1.php on line 3 Call Stack: 0.0741 322920 1. {main}() C:\xampp\htdocs\my_project\file1.php:0 Fatal error: require_once(): Failed opening required 'file2.php' (include_path='.;\xampp\php\PEAR') in C:\xampp\htdocs\my_project\file1.php on line 3 Call Stack: 0.0741 322920 1. {main}() C:\xampp\htdocs\my_project\file1.php:0 I tried require_once('./file2.php'); and require_once('.\file2.php'); since it is windows. I even added C:\xampp\htdocs\my_project\ to the projects include path and it shows up as such on the prject view and see file1.php and file2.php It doesn't show up on this error report, but possibly because Netbeans (or PHP ]) knows that C:\xampp\htdocs\my_project\ === . Any suggestions? Btw, I am new to Netbeans, so it i sprobably something very obvious.

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• Potential problems porting to different architectures

  - by Brendan Long

  I'm writing a Linux program that currently compiles and works fine on x86 and x86_64, and now I'm wondering if there's anything special I'll need to do to make it work on other architectures. What I've heard is that for cross platform code I should: Don't assume anything about the size of a pointer, int or size_t Don't make assumptions about byte order (I don't do any bit shifting -- I assume gcc will optimize my power of two multiplication/division for me) Don't use assembly blocks (obvious) Make sure your libraries work (I'm using SQLite, libcurl and Boost, which all seem pretty cross-platform) Is there anything else I need to worry about? I'm not currently targeting any other architectures, but I expect to support ARM at some point, and I figure I might as well make it work on any architecture if I can. Also, regarding my second point about byte order, do I need to do anything special with text input? I read files with getline(), so it seems like that should be done automatically as well.

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• Self hosted WCF console output from service

  - by user989056

  quick one: Is it possible to capture the output stream of a WCF service that is hosted via ServiceHost ( self hosted service) ? I have methods within my WCF service that output useful debugging information, is it possible to send these to it's host's console output? Edit: It appears that I have made an obvious blunder - I was using Debug instead of Console. It is possible to output to the console by using the standard Console output commands in your WCF service class. I have marked the answer that I have found the most useful.

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