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• Active Record Associations:

  - by jmccartie

  I'm brand new to Rails, so bear with me. I have 3 models: User, Section, and Tick. Each section is created by a user. My guess with this association: class Section < ActiveRecord::Base has_one :user end Next, each user can "tick" off a section -- only once. So for each tick, I have a section_id, user_id, and timestamps. Here's where I'm stuck. Does this call for a "has_one :through" association? If so, which direction? If not, then I'm way off. Which association works here? Thanks!

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• C Programming: calling free() on error?

  - by kouei

  Hi all, This a follow up on my previous question. link here. My question is: Let's say I have the following code.. char* buf = (char*) malloc(1024); ... for(; i<20; i++) { if(read(fd, buf, 1024) == -1) { // read off a file and store in buffer perror("read failed"); return 1; } ... } free(buf); what i'm trying to get at is that - what if an error occurs at read()? does that mean my allocated memory never gets freed? If that's the case, how do I handle this? Should I be calling free() as part of error handling? Once again, I apologize for the bad English. ^^; Many thanks, K.

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• assignment vs std::swap and merging and keeping duplicates in seperate object

  - by rubenvb

  Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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• Fastest tr:hover method

  - by Alex

  What is the single fastest method for table row hover css change? I've tried jQuery (onmouseover/out) and CSS with tr:hover, but once I make my page fullscreen (1920x1200) the performance on my grid is getting just sluggish enough to give the entire page a feel of being sub-par. That's on a grid with 25 rows, and some spans and divs per row. I've tried IE and Google Chrome. Is there another, faster method? What is generally considered the fastest method across browsers for doing hover CSS changes?

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• How to Tweet from multiple acounts with twitter Gem in Rails?

  - by Jmlevick

  I have an application wich has Oauth access using Twitter as provider. I also have the ability to ask the logged user permisson to Read and Write in his/her account and once a user authorized the app, I can send tweets as the user with something like: u = User.find(id) u.twitter.update("Some-Status-Here") in the rails console... What I want to do is to Tweet as all the users in one command, but if I try something like: u = User.all u.twitter.update("Some-Status-Here") I get this error: undefined method `twitter' for #<Array:0x00000002e2f188> How can I tweet as all the users in one command? What am I doing wrong? I feel it is a very basic thing I'm missing... Can someone help me? Thank You.

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• Drag and drop objects onto a DIV.. relative vs absolute position and size of target DIV

  - by Scott

  Hi, I have a question about drag and drop and hoping one of you already solved it. I have an online web app where I can drag and drop annotations (arrows, stars) on top of an image that sits on a DIV. Here's some things to know. 1) The image can be any size (sometimes big sometimes small) 2) The DIV of wrapper can be left aligned or centered 3) The DIV of wrapper can be fixed or auto So is there any possible solution to make it so positions of annotations are always relative to the top left corner of the image? So I am using jQuery. How would I get an annotation's position always relative to the top left corner of an image once I drop object? Thanks!

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• How can I ensure that JavaScript inserted via AJAX will be executed after the accompanying HTML (als

  - by RenderIn

  I've got portions of pages being replaced with HTML retrieved via AJAX calls. Some of the HTML coming back has JavaScript that needs to be run once in order to initialize the accompanying HTML (setting up event handlers). Since the document has already been loaded, when I replace chunks of HTML using jQuery's .html function, having jQuery(document).ready(function() {...}); doesn't execute since the page loaded long before and this is just a snippet of HTML being replaced. What's the best way to attach event handlers whose code is packaged along with the HTML it's interested in, when that content is loaded via AJAX? Should I just put a procedural block of javascript after the HTML , so that when I insert the new HTML block, jQuery will execute the javascript immediately? Is the HTML definitely in the DOM and ready to be acted upon by JavaScript which is in the same .html call?

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• Jquery disable link for 5 seconds

  - by John

  I have this code: $('#page-refresh').click( function() { $.ajax({ url: "/page1.php", cache: false, dataType: "html", success: function(data) { $('#pagelist').html(data); } }); return false; }); In this code is it possible that on the ajax success function it disables the #page-refresh click for 5 seconds then re-enable it? Basically if a person clicks the button and this action happens I dont want them to click and run this action again for another 5 seconds. I looked at delay() to unbind the click for this then bind it again but once it unbinded it never allowed me to click the button anymore.

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• Which is quicker? Memcache or file query? (using maxmind geoip.dat file)

  - by tomcritchlow

  Hi, I'm using Python on Appengine and am looking up the geolocation of an IP address like this: import pygeoip gi = pygeoip.GeoIP('GeoIP.dat') Location = gi.country_code_by_addr(self.request.remote_addr) (pygeoip can be found here: http://code.google.com/p/pygeoip/) I want to geolocate each page of my app for a user so currently I lookup the IP address once then store it in memcache. My question - which is quicker? Looking up the IP address each time from the .dat file or fetching it from memcache? Are there any other pros/cons I need to be aware of? For general queries like this, is there a good guide to teach me how to optimise my code and run speed tests myself? I'm new to python and coding in general so apologies if this is a basic concept. Thanks! Tom

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• Best ASP.NET Background Service Implementation

  - by Jason N. Gaylord

  What's the best implementation for more than one background service in an ASP.NET application? Timer Callback Timer timer = new Timer(new TimerCallback(MyWorkCallback), HttpContext, 5000, 5000); Thread or ThreadPool Thread thread = new Thread(Work); thread.IsBackground = true; thread.Start(); BackgroundWorker BackgroundWorker worker = new BackgroundWorker(); worker.DoWork += new DoWorkEventHandler(DoMyWork); worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(DoMyWork_Completed); worker.RunWorkerAsync(); Caching like http://www.codeproject.com/KB/aspnet/ASPNETService.aspx (located in Jeff Atwood's post here) I need to run multiple background "services" at a given time. One service may run every 5 minutes where another may be once a day. It will never be more than 10 services running at a time.

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• What is the preferred way to indent cases in a switch?

  - by neutrino

  Hey there, As I was writing another switch in Eclipse, I once again came across a rather weird (to me, at least) default indentation, which is applied to 'switch' statements: switch (i) { case 1: ... case n: ... } I tend to prefer another way: switch (i) { case 1: ... case n: ... } Which way is more readable and eye-pleasing for you? I'm still not hundred percent determined what's best for me, so I'd like to stick to what's best for other people who would read my code. BTW, you're free to close this question if this is too subjective. :)

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• Help with Oracle SQL Count function! =)

  - by user363024

  Hi guys.. The question im struggling with is this: i have a list of helicopter names in different charters and i need to find out WHICH helicopter has the least amount of charters booked. Once i find that out i need to ONLY display the one that has the least. I so far have this: SELECT Helicopter_Name COUNT (Distinct Charter_NUM) FROM Charter_Table GROUP BY Helicopter Name ^ this is where i am stuck, i realise MIN could be used to pick out the value that is the smallest but i am not sure how to integrate this into the command. Something like Where MIN = MIN Value Id really appreciate it

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• Determining the angle to fire a shot when target and shooter moves, and bullet moves with shooter velocity added in

  - by Azaral

  I saw this question: Predicting enemy position in order to have an object lead its target and followed the link in the answer to stack overflow. In the stack overflow page I used the 2nd answer, the one that is a large mathematical derivation. My situation is a little different though. My first question though is will the answer provided in the stack overflow page even work to begin with, assuming the original circumstances of moving target and stationary shooter. My situation is a little different than that situation. My target moves, the shooter moves, and the bullets from the shooter start off with the velocities in x and y added to the bullets' x and y velocities. If you are sliding to the right, the bullets will remain in front of you as you move so as long as your velocity remains constant. What I'm trying to do is to get the enemy to be able to determine where they need to shoot in order to hit the player. Unless the player and enemy is stationary, the velocity from the ship adding to the velocity of the bullets will cause a miss. I'd rather like to prevent that. I used the formula in the stack overflow answer and did what I thought were the appropriate adjustments. I've been banging at this for the last four hours and I just can't make it click. It is probably something really simple and boneheaded that I am missing (that seems to be a lot of my problems lately). Here is the solution presented from the stack overflow answer: It boils down to solving a quadratic equation of the form: a * sqr(x) + b * x + c == 0 Note that by sqr I mean square, as opposed to square root. Use the following values: a := sqr(target.velocityX) + sqr(target.velocityY) - sqr(projectile_speed) b := 2 * (target.velocityX * (target.startX - cannon.X) + target.velocityY * (target.startY - cannon.Y)) c := sqr(target.startX - cannon.X) + sqr(target.startY - cannon.Y) Now we can look at the discriminant to determine if we have a possible solution. disc := sqr(b) - 4 * a * c If the discriminant is less than 0, forget about hitting your target -- your projectile can never get there in time. Otherwise, look at two candidate solutions: t1 := (-b + sqrt(disc)) / (2 * a) t2 := (-b - sqrt(disc)) / (2 * a) Note that if disc == 0 then t1 and t2 are equal. If there are no other considerations such as intervening obstacles, simply choose the smaller positive value. (Negative t values would require firing backward in time to use!) Substitute the chosen t value back into the target's position equations to get the coordinates of the leading point you should be aiming at: aim.X := t * target.velocityX + target.startX aim.Y := t * target.velocityY + target.startY Here is my code, after being corrected by Sam Hocevar (thank you again for your help!). It still doesn't work. For some reason it never enters the section of code inside the if(disc = 0) (obviously because it is always less than zero but...). However, if I plug the numbers from my game log on the enemy and player positions and velocities it outputs a valid firing solution. I have looked at the code side by side a couple of times now and I can't find any differences. There has got to be something simple I'm missing here. If someone else could look at this code and determine what is going on here I'd appreciate it. I know it's not going through that section because if it were, shouldShoot would become true and the enemy would be blasting away at the player. This section calls the function in question, CalculateShootHeading() if(shouldMove) { UseEngines(); } x += xVelocity; y += yVelocity; CalculateShootHeading(); if(shouldShoot) { ShootWeapons(); } UpdateWeapons(); This is CalculateShootHeading(). This is inside the enemy class so x and y are the enemy's x and y and the same with velocity. One output from my game log gives Player X = 2108, Player Y = -180.956, Player X velocity = 10.9949, Player Y Velocity = -6.26017, Enemy X = 1988.31, Enemy Y = -339.051, Enemy X velocity = 1.81666, Enemy Y velocity = -9.67762, 0 enemy projectiles. The output from the console tester is Bullet position = 2210.49, -239.313 and Player Position = 2210.49, -239.313. This doesn't make any sense. The only thing that could be different is the code or the input into my function in the game and I've checked that and I don't think that it is wrong as it's updated before this and never changed. float const bulletSpeed = 30.f; float const dx = playerX - x; float const dy = playerY - y; float const vx = playerXVelocity - xVelocity; float const vy = playerYVelocity - yVelocity; float const a = vx * vx + vy * vy - bulletSpeed * bulletSpeed; float const b = 2.f * (vx * dx + vy * dy); float const c = dx * dx + dy * dy; float const disc = b * b - 4.f * a * c; shouldShoot = false; if (disc >= 0.f) { float t0 = (-b - std::sqrt(disc)) / (2.f * a); float t1 = (-b + std::sqrt(disc)) / (2.f * a); if (t0 < 0.f || (t1 < t0 && t1 >= 0.f)) { t0 = t1; } if (t0 >= 0.f) { float shootx = vx + dx / t0; float shooty = vy + dy / t0; heading = std::atan2(shooty, shootx) * RAD2DEGREE; } shouldShoot = true; }

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• Getting Different IP each time

  - by Sarfraz

  Hello, I am creating a poll script for a facebook fan page: http://www.facebook.com/apps/application.php?id=115400635147687&v=app_115400635147687 I am getting the IP using: $_SERVER['REMOTE_ADDR'] But the problem is that each time I refresh the page, or make an ajax call, the IP is changed everytime. Someone told me that facebook has many IPs, proxies. Basically I need to save the IP in database, so that once a user from certain IP has voted, he should not be able to do so again. What is the solution or alternative to this?

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• handling activity destruction in multithreaded android app

  - by Jayesh

  Hi, I have a multithreded app where background threads are used to load data over network or from disk/db. Every once in a while user will perform some action e.g. fetch news over network, which will spawn a background AsyncTask, but for some reason user will quit the app (press back button so that activity gets destroyed). In most such scenarios, I make appropriate checks in the background thread after it returns from n/w i/o, so that it won't crash by accessing members of the activity that is destroyed by now. However some corner cases are left where crashes happen, because the background thread would access some member of activity that is now null. Do other Android developers have some generic/recommended framework to handle such scenarios? These are the times when I wish android would have guaranteed termination of all threads when activity destroys (in the same way that regular linux process cleans up when it's quit)... but I guess Android devs had good reasons for not exposing process lifetimes through the api.

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• What are the most frustrating Python hacks to unwind, rewrite, etc.?

  - by Bialecki

  My impression of Python from the short time I've been developing with it is that it's incredible powerful and flexible, but I can't help but feel like "with great power comes great responsibility." So while I've read numerous blog posts about simple and elegant Python snippets that solve a problems, I wonder if there are design patterns or abuses of Python language features that, once built into an application or library, cause the code to be incredibly brittle and near impossible to refactor. So the question is basically what are the most frustrating, but somewhat common, Python "hacks" or language feature abuses that someone can introduce that will cause nightmares for future maintainers of that code?

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• What requests do browsers' "F5" and "Ctrl + F5" refreshes generate?

  - by Morgan Cheng

  Is there a standard for what actions F5 and Ctrl+F5 trigger in web browsers? I once did experiment in IE6 and Firefox 2.x. The "F5" refresh would trigger a HTTP request sent to the server with an "If-Modified-Since" header, while "Ctrl+F5" would not have such a header. In my understanding, F5 will try to utilize cached content as much as possible, while "Ctrl+F5" is intended to abandon all cached content and just retrieve all content from the servers again. But today, I noticed that in some of the latest browsers (Chrome, IE8) it doesn't work in this way anymore. Both "F5" and "Ctrl+F5" send the "If-Modified-Since" header. So how is this supposed to work, or (if there is no standard) how do the major browsers differ in how they implement these refresh features?

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• Click Function on jQuery plugin only allows for single click

  - by user1427307

  I've created this simple plugin to add multiple animations on click but the problem is that once the object is clicked it can not repeat the animation by clicking again, i can't figure out why the added class is not removing itself after the click function is complete to allow it to be clicked again and repeat.. any suggestions? (function($) { $.fn.vivify = function(options) { var defaults = { animation: 'bounce', }; var options = $.extend(defaults, options); return this.each(function() { var o = options; var obj = $(this); var animation = o.animation; obj.bind("click", function() { obj.addClass(o.animation); obj.addClass('vivify'); }, function() { obj.removeClass(o.animation); }); }) } })(jQuery);

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• Using True and False to select items to print

  - by user1753915

  I have a workbook that contains rows of information that needs to printed to a seperate worksheet in excel. I am trying to utilize a checkbox to indicate which items need to print and which items need to be skipped. The checkbox is located in column "A" and once checked and the macro ran, I want it to pick up the data in each cell of that particular row, transfer it a seperate worksheet (form), prompt and save the worksheet to pdf, clear the form, and then return to the main worksheet to continue until all rows have been checked. However, right now, my code is only looping through the very first "TRUE" statement and not continuing to the rest. Here is the code: Private Sub CommandButton1_Click() On Error GoTo ErrHandler: Dim i As Integer For i = 1 To 10 If ActiveSheet.OLEObjects("CheckBox" & i).Object.Value = False Then Else If ActiveSheet.OLEObjects("CheckBox" & i).Object.Value = True Then Call PrintWO Else End If Do Until ActiveSheet.OLEObjects("CheckBox" & i).Object.Value = 10 MsgBox "Nothing Selected to Print" Exit Do Exit Sub Loop End If Next i ErrHandler: End Sub

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• No such directory when committing files using CVS from Eclipse

  - by Peter

  Hi all I am using Eclipse solely as a CVS client. Mostly it works very good, but once in a while, when I am right-clicking a file to commit it (a file that it itself says is changed and ready for commit), it tells me "cvs [server aborted]: no such directory `...' But the directory DOES exist?! If I navigate to the folder using tortoise CVS and right click for commit, it works fine? (this is the way I finally have to get those files committed) Has anyone experienced this as well, and more importantly - has anyone solved it? :) I am running Vista on the client PC and the CVS server is a Windows Server 2003 (please dont tell me to just switch to Linux - that is not much help). Thank you very much for your help!

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• Is it "legal" for C++ runtime to call terminate() when the C++ code is used inside some non-C++ prog

  - by sharptooth

  In certain cases - especially when an exception escapes a destructor during stack unwinding - C++ runtime calls terminate() which must do something reasonable post-mortem and then exit the program. When a question "why so harsh" arises the answer is usually "there's nothing more reasonable to do in such error situations". That sounds reasonable if the whole program is in C++. Now what if the C++ code is in a library and the program that uses the library is not in C++? This happens quite often - for example I might have a native C++ COM component consumed by a .NET program. Once terminate() is called inside the component code the .NET program suddenly ends abnormally. The program author will first of all think "I don't care of C++, why the hell is this library make my program exit?" How do I handle the latter scenario when developing libraries in C++? Is it reasonable that terminate() unexpectedly ends the program? Is there a better way to handle such situations?

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• IIS Active Directory double handshake hickup

  - by AngryHacker

  I have a .net 2.0 click-once application that connects to IIS web services on Windows 2003 R2 64-bits. The IIS is setup with Integrated Windows Authentication. So whenever a web service call is made to IIS web services, there is a double handshake taking place: Client Request #1 GetEmployeeList Server Response #1 <- 401 HTTP/1.1 401 Unauthorized WWW-Authenticate: Negotiate WWW-Authenticate: NTLM Client Request #2 REQUEST Header... Server Response #2 <- 200 Data Received Lately, however, Server Response #1 will sometimes (a good 20 percent of the calls) take a massive amount of time (like 25 to 30 seconds). How do I debug this problem? Is this a Active Directory problem or a Domain Controller problem?

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• How do I load only a single wordpress post via the url?

  - by Jared

  Hello, We are currently undergoing some reworking of our website - in the meantime, I am looking for a quick a dirty fix. We have wordpress setup, so that no-so-tech-savvy employees can add events, news, etc. However, there are currently sections on our site dedicated to what would be tags in Wordpress. For instance, we have posts in WP with the tag "events." It's easy enough to display all posts with that tag, but I need to do a PHP include on our old site, and only show JUST THE POST. I can use a rss2html tool, but it strips out somethings like necessary tables. So how do Display only a single WP post, without anything else (no menus, settings, no Wp interface) via a URL? I could use a theme that is stripped down (by using something like theme switcher), but I need it to only load that theme once, not be the default theme....

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• How to create plots in multiple windows and keep them seperate in R

  - by PaulHurleyuk

  Hello SOers, I'm sure this is an easy problem, but my google / help foo has failed me, so it's up to you. I have an R script that generates several plots, and I want to view all the plots on screen at once (in seperate windows), but I can't work out how to open multiple graphics windows. I'm using ggplot2, but I feel this is a more basic problem, so I'm just using base grapics for this simple example x<-c(1:10) y<-sin(x) z<-cos(x) dev.new() plot(y=y,x=x) dev.off() dev.new() plot(x=x,y=z) But this doesn't work. I'm on Windows if this matters (Windows + Eclipse + StatEt)

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• IE downloads and installs CAB dialog popup upon every page refresh

  I have a signed cab on an aspx page. I am seeing the following inconsistent behavior. Any insights would be highly appreciated. On some machines, the cab is downloaded and installed on every page refresh. On few of those machines, the IE "install cab" dialog pops up on every page refresh, while on the others it pops up only once. Additional info: The CAB contains a .NET DLL The CAB is slightly large (around 30 MB), hence recurring download behavior is a pain Target browsers are IE6 and IE7, and the behavior is common to both!

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