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  • Overriding as_json has no effect?

    - by Ola Tuvesson
    I'm trying to override as_json in one of my models, partly to include data from another model, partly to strip out some unnecessary fields. From what I've read this is the preferred approach in Rails 3. To keep it simple, let's say I've got something like: class Country < ActiveRecord::Base def as_json(options={}) super( :only => [:id,:name] ) end end and in my controller simply def show respond_to do |format| format.json { render :json => @country } end end Yet whatever i try, the output always contains the full data, the fields are not filtered by the ":only" clause. Basically, my override doesn't seem to kick in, though if I change it to, say... class Country < ActiveRecord::Base def as_json(options={}) {foo: "bar"} end end ...I do indeed get the expected JSON output. Have I simply got the syntax wrong?

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  • Django equivalent for latest entry for each user

    - by paul-ogrady
    Hi, I'm surprised this question hasn't come up. Couldn't find much on the web. Using Entry.objects.latest('created_at') I can recover the latest entry for all Entry objects, but say if I want the latest entry for each user? This is something similar to an SQL latest record query. But how do I achieve this using the ORM? Here is my approach I'm wondering if it is the most efficient way to do what I want. First I perform a sub query: Objects are grouped by user and the Max (latest) created_by field is returned for each user (created_at__max) I then filter Entry objects based on the results in the subquery and get the required objects. Entry.objects.filter(created_at__in=Entry.objects.values('user').annotate(Max('created_at')).values_list('created_at__max')) or using a manager: class UsersLatest(models.Manager): def get_query_set(self): return Super(UsersLatest,self).get_query_set().filter(created_at__in=self.model.objects.values('user').annotate(Max('created_at')).values_list('created_at__max')) Is there a more efficient way? possibly without sub query? Thanks, Paul

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  • comparing two angles

    - by Elazar Leibovich
    Given four points in the plane, A,B,X,Y, I wish to determine which of the following two angles is smaller ?ABX or ?ABY. I'd rather not use cos or sqrt, in order to preserve accuracy. In the case where A=(-1,0),B=(0,0), I can compare the two angles ?ABX and ?ABY, by calculating the dot product of the vectors X,Y, and watch it's sign. What I can do in this case is: Determine whether or not ABX turns right or left If ABX turns left check whether or not Y and A are on the same side of the line on segment BX. If they are - ?ABX is a smaller than ABY. If ABX turns right, then Y and A on the same side of BX means that ?ABX is larger than ?ABY. But this seems too complicated to me. Any simpler approach?

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  • managing library dependencies with Boost.Build and C++

    - by user931794
    I want to develop a project which can be built on a bunch of different platforms. The project code will be in C++, what's the the best way to manage libraries? I plan on using bjam as the build system because I'm going to be depending on Boost and their unit testing framework as well. The two dependent libraries are Boost itself and FLTK. The possibilities that come to mind for library management are: include build artifacts (binaries) and headers for all supported platforms in-tree include complete source for all dependent libraries in-tree, and somehow script them as dependencies A combination of 1 and 2, like node.js does with v8 inform the user that they need to build the libraries themselves and then have them on the PATH or in some special directory, like libcurl does with its dependencies What is the best approach here? The project will probably not grow beyond a few thousand lines over the next six months, but I want to make the right choice here so that I don't have to come back and switch everything around later.

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  • How to include javascript/css once with Struts 1.x

    - by Felix
    If this is the wrong approach, please suggest something better, but my current efforts have been trying to find something that exists for a single page load, such that I can cache which javascript/css files have been included so as to only include them once. I thought in a TagSupport subclass I could use (HttpServletRequest)pageContext.getRequest().getParameterMap().put(srcKey,true) but the request is per jsp, not per page load so it was a failure. I could set up a filter in web.xml, but it seems I would have to search the response for duplicates and rewrite the response...pain. I could try to store things in the session, but there are headaches with clearing values... Any help would be appreciated.

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  • OpenMP + SSE gives no speedup

    - by Sayan Ghosh
    Hi, My Professor found out this interesting experiment of 3D Linearly separable Kernel Convolution using SSE and OpenMP, and gave the task to me to benchmark the statistics on our system. The author claims a crazy 18 fold speedup from the serial approach! Might not be always, but we were expecting at least a 2-4 times speedup running this on a Dual Core Intel. http://software.intel.com/en-us/articles/16bit-3d-convolution-sse4openmp-implementation-on-penryn-cpu/#comment-41994 Alas, we could find exactly no speedup. The serial code performs always better, with or without OpenMP. I am using Linux, and observed a certain trend...when no other processes are running on the system, after a while the loadavg starts increasing, and the the %CPU utilization falls down. Another probable false positive which I ran into accidentally...I started the program, then immediately paused it. Then I ran it on background with bg, and saw a speedup of more than 2. This happens all the time! Any advice would be great. Thanks, Sayan

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  • Tips on creating a "build a bracelet" app

    - by Felipe Caldas
    I have an idea for an app/game which is basically a build your own bracelet. I will give to the user, say, 5 different types of beads, and the user and drag those beads into a line that is previously drawn in the screen and create his/her bracelet. I am now thinking on the best way to approach this. Would be using the android's OpenGL libraries (and therefore, creating the beads and loading its textures) the best and easiest way? Ultimately, I would like to push new beads into the application whenever I have a new bead texture. Thanks, Felipe

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  • How can I "best fit" an arbitrary cairo (pycairo) path?

    - by Daniel Straight
    It seems like given the information in stroke_extents() and the translate(x, y) and scale(x, y) functions, I should be able to take any arbitrary cairo (I'm using pycairo) path and "best fit" it. In other words, center it and expand it to fill the available space. Before drawing the path, I have scaled the canvas such that the origin is the lower left corner, up is y+, right is x+, and the height and width are both 1. Given these conditions, this code seems to correctly scale the path: # cr is the canvas extents = cr.stroke_extents() x_size = abs(extents[0]) + abs(extents[2]) y_size = abs(extents[1]) + abs(extents[3]) cr.scale(1.0 / x_size, 1.0 / y_size) I cannot for the life of me figure out the translating though. Is there a simpler approach? How can I "best fit" a cairo path on its canvas? Please ask for clarification if anything is unclear in this question.

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  • Linq sql Attach, Update Check set to Never, but still Concurrency conflicts

    - by remdao
    In the dbml designer I've set Update Check to Never on all properties. But i still get an exception when doing Attach: "An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported." This approach seems to have worked for others on here, but there must be something I've missed. using(TheDataContext dc = new TheDataContext()) { test = dc.Members.FirstOrDefault(m => m.fltId == 1); } test.Name = "test2"; using(TheDataContext dc = new TheDataContext()) { dc.Members.Attach(test, true); dc.SubmitChanges(); }

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  • What are the pros and cons of using an in memeory DB rather than a ThreadLocal

    - by Pangea
    we have been using ThreadLocal so far to carry some data so as to not clutter the API. However below are some of issues of using thread local that which I dont like 1) over the years the data items being carried in thread local has increased 2) Since we started using threads (for some light weight processing), we have also migrating these data to the threads in the pool and copying them back again I am thinking of using an in memory DB for these (we doesnt want to add this to the API). I wondering if this approach is good. What r the pros and cons. thx in advance.

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  • How to prevent column b containing the same value as any column a in Oracle?

    - by Janek Bogucki
    What is a good way to prevent a table with 2 columns, a and b, from having any record where column b is equal to any value in column a? This would be used for a table of corrections like this, MR -> Mr Prf. -> Prof. MRs -> Mrs I can see how it could be done with a trigger and a subquery assuming no concurrent activity but a more declarative approach would be preferable. This is an example of what should be prevented, Wing Commdr. -> Wing Cdr. Wing Cdr. -> Wing Commander Ideally the solution would work with concurrent inserts and updates.

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  • How do I access variables with hyphenated names in Smarty?

    - by abeger
    I've got a PHP page that parses an XML file with SimpleXml, then passes that object to a Smarty template. My problem is that the XML file has hyphens in its tag names, e.g. video-player. In PHP, this is no problem, I just use $xml->{'video-player'} and everything's fine. Smarty, on the other hand, throws a fit when I try to use that syntax. The only solution I've come up with so far is to use a variable to store the name, e.g., { assign var=name value="video-player" } { $xml->$name } But this isn't terribly graceful to say the least. Is there another, better, approach to referring to a hyphenated variable name in Smarty?

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  • Restart IIS7 webapp for debug in VS2008

    - by spender
    I'm developing an ASP.NET asyc generic handler which uses a static System.Threading.Timer instance to feed data to the response output stream while the context is in the asynchronous phase. I'm having issues at startup that I'd like to debug. Currently, because of the long-lived nature of the timer, I'm manually killing w3wp.exe in order to cause the application to restart. I'm aware that there are other ways to do this, but this is the best workflow I can find! Isn't there a way to force a cold start when I hit f5, instead of the standard VS approach of attaching to the existing IIS process?

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  • [Java] Form data transition into entity beans to persist them by the server side ORM

    - by cscsaba242
    Hello guys, Is there any good explanation or tutorial which describes the common way how can we create entity beans from the received data of the form ? The main reason of my question the treating the received ids (e.g id of country,city and so forth) which is the way from the id to entity ? Example: ................Client side form username:String countryid:Integer (could be a drop down) ................Server side entities public class UserBean { String username; CountryBean Country; } public class CountryBean { String cityname; Integer id; } ............................................ Maybe the question is dependent of the used technology, but I guess there is a very common way. I would like to comprehend the conventional approach of this problem. (For the sake of the completeness I would like to save the form data (received by Stripes) by JPA) Thanks advance. cscsaba242

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  • scanf("%d", char*) - char-as-int format string?

    - by SF.
    What is the format string modifier for char-as-number? I want to read in a number never exceeding 255 (actually much less) into an unsigned char type variable using sscanf. Using the typical char source[] = "x32"; char separator; unsigned char dest; int len; len = sscanf(source,"%c%d",&separator,&dest); // validate and proceed... I'm getting the expected warning: argument 4 of sscanf is type char*, int* expected. As I understand the specs, there is no modifier for char (like %sd for short, or %lld for 64-bit long) is it dangerous? (will overflow just overflow (roll-over) the variable or will it write outside the allocated space?) is there a prettier way to achieve that than allocating a temporary int variable? ...or would you suggest an entirely different approach altogether?

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  • NSKeyedArchiver save method ( that i made) crashed the iphone simulator

    - by Kevin
    i saw this approach on a tutorial, and the message is working for their example but when i implement this it does not work. from what i can tell the iphone simulator crashes when i do a [ self saveSettingsData]. TheSettings is class object that i declare and initialize in the appdelagate with these methods. the error says terminating due to uncaught exception. i am new to the iphone sdk and objective, so i really can't figure out what is going on thanks to any one who can help, i am ready to literally pull my hair out. (NSString *) SettingsDataFilePath { NSString * settingsDataFilePath ; NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) ; NSString * documentsDirectory = [paths objectAtIndex:0] ; settingsDataFilePath = [[documentsDirectory stringByAppendingPathComponent: @"SetggggtingsData.plist" ] retain] ; return settingsDataFilePath ; } (void) saveSettingsData { [NSKeyedArchiver archiveRootObject:[TheSettings copy] toFile:[self SettingsDataFilePath]] ;

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  • How To Aggregate API Data?

    - by Mindblip
    Hi, I have a system that connects to 2 popular APIs. I need to aggregate the data from each into a unified result that can then be paginated. The scope of the project means that the system could end up supporting 10's of APIs. Each API imposes a max limit of 50 results per request. What is the best way of aggregating this data so that it is reliable i.e ordered, no duplicates etc I am using CakePHP framework on a LAMP environment, however, I think this question relates to all programming languages. My approach so far is to query the search API of each provider and then populate a MySQL table. From this the results are ordered, paginated etc. However, my concern is performance: API communication, parsing, inserting and then reading all in one execution. Am I missing something, does anyone have any other ideas? I'm sure this is a common problem with many alternative solutions. Any help would be greatly appreciated. Thanks, Paul

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  • Piping SoX in Python - subprocess alternative?

    - by Cochise Ruhulessin
    I use SoX in an application. The application uses it to apply various operations on audiofiles, such as trimming. This works fine: from subprocess import Popen, PIPE kwargs = {'stdin': PIPE, 'stdout': PIPE, 'stderr': PIPE} pipe = Popen(['sox','-t','mp3','-', 'test.mp3','trim','0','15'], **kwargs) output, errors = pipe.communicate(input=open('test.mp3','rb').read()) if errors: raise RuntimeError(errors) This will cause problems on large files hower, since read() loads the complete file to memory; which is slow and may cause the pipes' buffer to overflow. A workaround exists: from subprocess import Popen, PIPE import tempfile import uuid import shutil import os kwargs = {'stdin': PIPE, 'stdout': PIPE, 'stderr': PIPE} tmp = os.path.join(tempfile.gettempdir(), uuid.uuid1().hex + '.mp3') pipe = Popen(['sox','test.mp3', tmp,'trim','0','15'], **kwargs) output, errors = pipe.communicate() if errors: raise RuntimeError(errors) shutil.copy2(tmp, 'test.mp3') os.remove(tmp) So the question stands as follows: Are there any alternatives to this approach, aside from writing a Python extension to the Sox C API?

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  • c# binarysearch a list<T> by a member of T

    - by Pygmy
    I have a baseclass Event with a DateTime member TimeStamp. Lots of other event-classes will derive from this. I want to be able to search a list of events (that can contain events with duplicate timestamps) fast, so I'd like to use a binary search. So I started out writing something like this : public class EventList<T> : List<T> where T : Event { private IComparer<T> comparer = (x, y) => Comparer<DateTime>.Default.Compare(x.TimeStamp, y.TimeStamp); public IEnumerable<T> EventsBetween(DateTime inFromTime, DateTime inToTime) { // Find the index for the beginning. int index = this.BinarySearch(inFromTime, comparer); // BLAH REST OF IMPLEMENTATION } } The problem is that the BinarySearch only accepts T (so - an Event type) as parameter, while I want to search based on a member of T - the TimeStamp. What would be a good way to approach this ?

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  • Is it safe to lock a static variable in a non-static class?

    - by Dario Solera
    I've got a class that manages a shared resource. Now, since access to the resource depends on many parameters, this class is instantiated and disposed several times during the normal execution of the program. The shared resource does not support concurrency, so some kind of locking is needed. The first thing that came into my mind is having a static instance in the class, and acquire locks on it, like this: // This thing is static! static readonly object MyLock = new object(); // This thing is NOT static! MyResource _resource = ...; public DoSomeWork() { lock(MyLock) { _resource.Access(); } } Does that make sense, or would you use another approach?

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  • Avoiding Redundancies in XML documents

    - by MarceloRamires
    I was working with a certain XML where there were no redundancies <person> <eye> <eye_info> <eye_color> blue </eye_color> </eye_info> </eye> <hair> <hair_info> <hair_color> blue </hair_color> </hair_info> </hair> </person> As you can see, the sub-tag eye-color makes reference to eye in it's name, so there was no need to avoid redundancies, I could get the eye color in a single line after loading the XML into a dataset: dataset.ReadXml(path); value = dataset.Tables("eye_info").Rows(0)("eye_color"); I do realise it's not the smartest way of doing so, and this situation I'm having now wasn't unforeseen. Now, let's say I have to read xml's that are in this format: <person> <eye> <info> <color> blue </color> </info> </eye> <hair> <info> <color> blue </color> </info> </hair> </person> So If I try to call it like this: dataset.ReadXml(path); value = dataset.Tables("info").Rows(0)("color"); There will be a redundancy, because I could only go as far as one up level to identify a single field in a XML with my previous method, and the 'disambiguator' is three levels above. Is there a practical way to reach with no mistake a single field given all the above (or at least a few) fields ?

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  • Getting a char array from a vector<int>?

    - by Legend
    I am trying to pass a value from C++ to TCL. As I cannot pass pointers without the use of some complicated modules, I was thinking of converting a vector to a char array and then passing this as a null terminated string (which is relatively easy). I have a vector as follows: 12, 32, 42, 84 which I want to convert into something like: "12 32 42 48" The approach I am thinking of is to use an iterator to iterate through the vector and then convert each integer into its string representation and then add it into a char array (which is dynamically created initially by passing the size of the vector). Is this the right way or is there a function that already does this?

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  • How to find a coding buddy

    - by Lirik
    I was reading Jeff Atwood's blog and he mentioned that he was suffering from code-paralysis (he called it analysis paralysis, but I feel like it's also code paralysis) when he didn't have a code buddy: http://www.codinghorror.com/blog/ Unfortunately I think that Jeff has set the bar a bit high, because he only works with developers who are really amazing. The only reason really amazing developers would work with me is if I was really amazing too, but sometimes I don't feel that amazing... the only thing I feel is that if I had a coding buddy I could be amazing :). I'm working on a project and I don't have many friends that are programmers, let alone friends that have time to spend on extracurricular activities. Jeff seems to have been able to find like-minded people that are actually willing to work together. I feel like I'm in a code-paralysis stage too and I need some coding buddies, where would I find some? How would I approach them?

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  • How would I best address this object type heirachy? Some kind of enum heirarchy?

    - by FerretallicA
    I'm curious as to any solutions out there for addressing object heirarchies in an ORM approach (in this instance, using Entity Framework 4). I'm working through some docs on EF4 and trying to apply it to a simple inventory tracking program. The possible types for inventory to fall into are as follows: INVENTORY ITEM TYPES: Hardware PC Desktop Server Laptop Accessory Input (keyboards, scanners etc) Output (monitors, printers etc) Storage (USB sticks, tape drives etc) Communication (network cards, routers etc) Software What recommendations are there for handling enums in a situation like this? Are enums even the solution? I don't really want to have a ridiculously normalised database for such a relatively simple experiment (eg tables for InventoryType, InventorySubtype, InventoryTypeToSubtype etc). I don't really want to over-complicate my data model with each subtype being inherited even though no additional properties or methods are included (except PC types which would ideally have associated accessories and software but that's probably out of scope here). It feels like there should be a really simple, elegant solution to this but I can't put my finger on it. Any assistance or input appreciated!

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  • Objective-C Plugin Architecture Security (Mac, not iphone)

    - by Tom Dalling
    I'm possibly writing a plugin system for a Cocoa application (Mac, not iphone). A common approach is the make each plugin a bundle, then inject the bundle into the main application. I'm concerned with the security implications of doing this, as the bundle will have complete access to the Objective-C runtime. I am especially concerned with a plugin having access to the code that handles registration and serial keys. Another plugin system we are considering is based on distributed notifications. Basically, each plugin will be a separate process, and they will communicate via distributed notifications only. Is there a way to load bundles securely (e.g. sandboxing)? If not, do you see any problems with using distributed notifications? Are there any other plugin architectures that would be better?

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