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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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• Including the functionality of a tool within another program?

  - by darren

  Hi there I would like to write an application, for my own interest, that graphically visualizes some network concepts. Basically I would like to show the output from tools like ping, traceroute and nmap. The most obvious approach seems to be to use pipes to call out to these tools from my C program, and process the information they return. However, I would like to avoid this heavy-handed approach if possible. My question is, is it possible to somehow link against these tools, or are there APIs that can be used to gain programatic access instead? If so, is this behavior available on a tool-by-tool basis only? One reason for wanting to do this is to keep everything in a single process / address space and to avoid dependance on these external tools. For example, if I wrote an iphone application, I would not be able to spawn processes to call out to the external tools themselves. Thanks for any advice or suggestions.

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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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• 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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• 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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• 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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• Whats the best data-structure for storing 2-tuple (a, b) which support adding, deleting tuples and c

  - by bhups

  Hi So here is my problem. I want to store 2-tuple (key, val) and want to perform following operations: - keys are strings and values are Integers - multiple keys can have same value - adding new tuples - updating any key with new value (any new value or updated value is greater than the previous one, like timestamps) - fetching all the keys with values less than or greater than given value - deleting tuples. Hash seems to be the obvious choice for updating the key's value but then lookups via values will be going to take longer (O(n)). The other option is balanced binary search tree with key and value switched. So now lookups via values will be fast (O(lg(n))) but updating a key will take (O(n)). So is there any data-structure which can be used to address these issues? 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• Bash variable kills script execusion

  - 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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• 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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• C# ASP.NET Update database with datatable

  - by Sir Graystar

  Scenario: I'm just trying to update my database with the changes made by the user to their information. Here is my code: SqlCommandBuilder cb = new SqlCommandBuilder(da); dt.Rows[0][2] = txtname.Text; dt.Rows[0][3] = txtinterests.Text; dt.Rows[0][4] = txtlocation.Text; da.SelectCommand = new SqlCommand(sqlcommand, conn); da.Update(dt); I know its going to be something obvious, but what have I missed? There are no errors, everything compiles correctly, but nothing happens. The record remains unchanged.

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• Captcha Alternative, how secure?

  - by aslum

  I do the web page for my local library, and I was thinking it might be kind of appealing to have a "custom" captcha based on book covers. So serve up one of several dozen book covers, and have the patron filling out the form type the book title to prove they're human. Assuming I stripped the title/author info from the image and filename, would that be enough? Would the fact that it was a unique system on a fairly small website be enough to make it effective? Just how tricky are the spam bots these days? Would having the image name be the ISBN # be too obvious?

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• Writing shorter code/algorithms, is more efficient (performance)?

  - by Carlos

  After coming across the code golf trivia around the site it is obvious people try to find ways to write code and algorithms as short as the possibly can in terms of characters, lines and total size, even if that means writing something like: n=input() while n>1:n=(n/2,n*3+1)[n%2];print n So as a beginner I start to wonder whether size actually matters :D. It is obviously a very subjective question highly dependent on the actual code being used, but what is the rule of thumb in the real world. In the case that size wont matter, how come then we don't focus more on performance rather than size?

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• Trouble with Canvas rendering in Safari/Opera

  - by Jon

  Been banging my head against this one for a while, and figured I'd turn to the experts for some advice. I've made a jQuery snippet that grabs the values from a table and plots them in a line graph on a canvas element (also generated by the JS). All's well in Firefox and Chrome, but Safari and Opera aren't displaying the plotted points. I've reviewed in Firebug, Web Inspector debugger, JSLint, and checked the markup with the w3 validator, but still can't find anything glaringly obvious. Any chance one of you guys could help me out? Here's a page with a simplified example: http://bit.ly/aAshPQ Thanks!

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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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• How to set a __str__ method for all ctype Structure classes?

  - by Reuben Thomas

  [Since asking this question, I've found: http://www.cs.unc.edu/~gb/blog/2007/02/11/ctypes-tricks/ which gives a good answer.] I just wrote a __str__ method for a ctype-generated Structure class 'foo' thus: def foo_to_str(self): s = [] for i in foo._fields_: s.append('{}: {}'.format(i[0], foo.\_\_getattribute__(self, i[0]))) return '\n'.join(s) foo.\_\_str__ = foo_to_str But this is a fairly natural way to produce a __str__ method for any Structure class. How can I add this method directly to the Structure class, so that all Structure classes generated by ctypes get it? (I am using the h2xml and xml2py scripts to auto-generate ctypes code, and this offers no obvious way to change the names of the classes output, so simply subclassing Structure, Union &c. and adding my __str__ method there would involve post-processing the output of xml2py.)

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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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