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  • Resource mapping in a Ruby on Rails URL (RESTful API)

    - by randombits
    I'm having a bit of difficulty coming up with the right answer to this, so I will solicit my problem here. I'm working on a RESTFul API. Naturally, I have multiple resources, some of which consist of parent to child relationships, some of which are stand alone resources. Where I'm having a bit of difficulty is figuring out how to make things easier for the folks who will be building clients against my API. The situation is this. Hypothetically I have a 'Street' resource. Each street has multiple homes. So Street :has_many to Homes and Homes :belongs_to Street. If a user wants to request an HTTP GET on a specific home resource, the following should work: http://mymap/streets/5/homes/10 That allows a user to get information for a home with the id 10. Straight forward. My question is, am I breaking the rules of the book by giving the user access to: http://mymap/homes/10 Technically that home resource exists on its own without the street. It makes sense that it exists as its own entity without an encapsulating street, even though business logic says otherwise. What's the best way to handle this?

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  • Why is this Java Calendar comparison bad?

    - by joe7pak
    Hello folks. I'm having an inexplicable problem with the Java Calendar class when I'm trying to compare to dates. I'm trying to compare to Calendars and determine if their difference is than 1 day, and do things bases on that difference or not. But it doesn't work. If I do this with the two dates: String currDate = aCurrentUTCCalendar.getTime().toString(); String localDate = aLocalCalendar.getTime().toString(); I get these results: currDate = "Thu Jan 06 05:58:00 MST 2010" localDate = "Tue Jan 05 00:02:00 MST 2010" This is correct. But if I do this: long curr = aCurrentUTCCalendar.getTime().getTime(); long local = aLocalCalendar.getTime().getTime(); I get these results: ( in milliseconds since the epoch ) curr = -125566110120000 local = 1262674920000 Since there is only about a 30 hour different between the two, the magnitudes are vastly different, not to mention that annoying negative sign. This causes problems if I do this: long day = 60 * 60 * 24 * 1000; // 86400000 millis, one day if( local - curr > day ) { // do something } What's wrong? Why are the getTime().toString() calls correct, but the getTime().getTime() calls are vastly different? I'm using jdk 1.6_06 on WinXP. I can't upgrade the JDK for various reasons.

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  • How do i set the Transaction Isolation in EJB?

    - by Nitesh Panchal
    Hello, I am not able to find a way to set TransactionIsolation in ejb. Can anybody tell me how do i set it? I am using persistence. I have looked the following classes : EntityManager , EntityManagerFactory, UserTransaction. None of them seems to have any method like setTransactionIsolation or such. Do we need to change persistence.xml? I just read a book named Mastering EJB 3.0 4th edition. They gave a full 10 page theory about Isolation level that this problems occur and that occurs and such things but at the end they gave this paragraph :- "As we now know, the EJB standard does not deal with isolation levels directly, and rightly so. EJB is a component specification. It defines the behavior and contracts of a business component with clients and middleware infrastructure (containers) such that the component can be rendered as various middleware services properly. EJBs therefore are transactional components that interact with resource managers, such as the JDBC resource manager or JMS resource manager, via JTS, as part of a transaction. They are not, hence, resource components in themselves. Since isolation levels are very specific to the behavior and capabilities of the underlying resources, they should therefore be specified at the resource API levels. " What exactly does it mean? What is meant by resource level APIs? Please help me. If persistence has no way to set Isolation Level then why do they give such huge theory in an EJB book and make it heavy in weight unnecessarily :(

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  • open current page in new window including query string

    - by Hatch
    First of all, I am a total dud at all things related to web developement, so please bear with me here. I suspect this question is laughable for the web guys, but unfortunately I can't figure this out. Here goes: I have an application, that does some processing, writes some result files and then displays the results in an embedded IE browser control. This is done by navigating the browser control to a local html file together with a query string containing the generated result files to display it all. The link target would look something like: c:\SomeFolder\results.htm?results=file%201.xml;file%202.xml;file%203.xml So far, everything's fine. However, in the html page is a href that is suppossed to open up the exact same just in a normal browser window. What I thought would work is: <a href="#" target="_blank">Show in browser</a> Since it is a link in an html page displayed in an IE control, the link will open up in IE no matter what the default browser might be. This works for IE7 and 8, but not for IE6. With IE6 the query string gets cut off and the browser opens file://c:/results/results.htm# without the query string. I am sure there must be a much better way to do this without the # and which would work in all IEs. How would the pros solve this?

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  • Plotting a graph with GD

    - by Nayena
    Here it goes. I have been thinking about this for a long time, and havent really been able to put up a proper way to do it yet. I havent implemented anything yet, as im still designing the thing. The idea is that i crawl a website for internal links, i got this settled, its easy, but after the crawling, i end up with an array with lots of links, and how many times those particular link appears on the site that i crawled (and how they're connected). With this huge array, i want to draw a graph somehow. Assuming i can handle the data correctly, the real question here is how i can draw this in a image by the use of the GD library. I figured if theres less than 12 elements, i can align them up on a unit circle spacing them up as a circle and then connecting them accordingly, so anything up to 12 elements shouldn't be a problem, but if theres more than 12, it could be awesome getting them lined up like this Or well, thats just a rough drawing, but i guess its just to prove a point. So i'm here looking for guidance or tips towards getting the math down to getting the stuff lined up in a good way. I have previously made bar-graphs, so i have little experience doing math with GD. If possible, id prefer not using some plotter-library - in the end, it gives me a better understanding on how things are supposed to be.

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  • Have you dealt with space hardening?

    - by Tim Post
    I am very eager to study best practices when it comes to space hardening. For instance, I've read (though I can't find the article any longer) that some core parts of the Mars rovers did not use dynamic memory allocation, in fact it was forbidden. I've also read that old fashioned core memory may be preferable in space. I was looking at some of the projects associated with the Google Lunar Challenge and wondering what it would feel like to get code on the moon, or even just into space. I know that space hardened boards offer some sanity in such a harsh environment, however I'm wondering (as a C programmer) how I would need to adjust my thinking and code if I was writing something that would run in space? I think the next few years might show more growth in private space companies, I'd really like to at least be somewhat knowledgeable regarding best practices. Can anyone recommend some books, offer links to papers on the topic or (gasp) even a simulator that shows you what happens to a program if radiation, cold or heat bombards a board that sustained damage to its insulation? I think the goal is keeping humans inside of a space craft (as far as fixing or swapping stuff) and avoiding missions to fix things. Furthermore, if the board maintains some critical system, early warnings seem paramount.

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  • How the reading from and writing to sockets are synchronized?

    - by Roman
    We create a socket. On one side of the socket we have a "server" and on another side there is a "client". Both, the server and client, can write to and read from the socket. It is what i understand. I do not understand the following things: If a server reads from the socket, does it see in the socket only those stuff which was written to the socket by the client? I mean if server writes something to the socket and than reads from the socket, will it (server) see in the socket the stuff it (server) wrote there? I hope not. Let's consider the following situation. A client write something to the socket and then it writes something new to the socket and then server reads from the socket. What will the server see there? Only the "new" stuff written by the client or both "new" and "old" one? If a client (or server) writes to the socket, can it see if the written information was received by other side? For example out.println("Hello, Server!") will return true it server received this message.

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  • HELP ME !! I am Not able to update form data to mysql using php and jquery

    - by Jimson Jose
    i tired and was unable to find the answer i am looking for an answer. my problem is that i am unable to update the values enterd in the form. I have attached all the files i'm using MYSQL database to fetch data. what happens is that i'm able to add and delete records from form using jquery and PHP scripts to MYSQL database, but i am not able to update data which was retrived from database. the file structure is as follows index.php is a file with jquery functions where it displays form for adding new data to MYSQL using save.php file and list of all records are view without refrishing page (calling load-list.php to view all records from index.php works fine, and save.php to save data from form) - Delete is an function called from index.php to delete record from mysql database (function calling delete.php works fine) - Update is an function called from index.php to update data using update-form.php by retriving specific record from mysql tabel, (works fine) Problem lies in updating data from update-form.php to update.php (in which update query is wrriten for mysql) i had tried in many ways at last i had figured out that data is not being transfred from update-form.php to update.php there is a small problem in jquery ajax function where it is not transfering data to update.php page. some thing is missing in calling update.php page it is not entering into that page I am new bee in programming i had collected this script from many forums and made this one.So i was limited in solving this problem i cam to know that this is good platform for me and many where we get a help to create new things.. please guide me with your help to complete my effors !!!!! i will be greatfull to all including ths site which gave me an oppurtunity to present my self..... please find the link below to download all files which is of 35kb (virus free assurance) download mysmallform files in ZIPped format, including mysql query thanks a lot in advance, May GOD bless YOU and THIS SITE

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  • Reading JSON with Javascript/jQuery

    - by Josephine
    I'm building a game in javascript/html5 and I'm trying to build a database of locked doors in a maze that can be loaded from and overwritten to throughout gameplay. I've found a large number of tutorials online, but nothing is working. I was wondering if someone could look at what I'm trying and let me know what I'm doing wrong. My JSON file looks like this: { "doors": [ {"left":true, "right":false, "bottom":false}, {"left":false, "right":false, "bottom":false}, {"right":false, "bottom":false, "top":false}, {"left":false, "right":false, "top":false} ] } I want to build the HTML page so that when a player collides with a door it checks if its locked or not like: if (player.x < leftDoor.x + leftDoor.width && player.x + player.width > leftDoor.x && player.y < leftDoor.y + leftDoor.height && player.y + player.height > leftDoor.y) { if(doors[0].left == true) alert("door is locked"); else window.location = ( "2.html?p1="); } However I'm having trouble reading from the JSON file itself. I've tried things like: function loadJson() { $(document).ready(function() { $.getJSON('info.json', function(doors) { alert(doors[0].left); }); }); } But nothing happens, and I need to be able to access the information in the HTML as well. I'd rather use jQuery, but I'm not opposed to straight JS if it works. I've been trying to do this for ages and I'm getting absolutely no where. If someone could help that would be amazing. Thanks!

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  • flex 4 release changes to application are not showing up.

    - by guacamoly
    I just took over a clients flex project and I can't get the app to reflect even a simple trace statement. Before I took over, the project was last successfully built using the Flash Builder Beta 2 environment/sdk. I have the latest release version of Flash Builder 4. Upon importing the project into FB4, I got a ton of errors. Most of them mostly because of the changes made to the sdk from beta2 to release. Some of the things I corrected: - mx namespace from library://ns.adobe.com/flex/halo to library://ns.adobe.com/flex/mx - video player skinning: a lot of the state names for the video player component had been changed, more required states had been added. also there were other video related component and property names that had to be updated. But I fixed all that and the application was finally able to compile (although with some warnings mostly of the duplicate variable type) The only thing now is that whatever change I make to the project doesn't get reflected in the build (debug or release). I changed existing traces, added additional traces. Nothing shows up. I even removed the applicationComplete property in the main.mxml. Everything still ran like nothing changed. Also I can't seem to debug the app. Whenever I try to debug.. flash builder says.. "Swf Application doesn't contain the required debugging information ... " Anyone have any idea how I need to even begin tackling all this? Any help or pointers would be greatly appreciated.

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  • Ruby core documentation quality

    - by karatedog
    I'm relatively new to Ruby and have limited time therefore I try out simple things. Recently I needed to create a file and because I'm lazy as hell, I run to Google. The result: File.open(local_filename, 'w') {|f| f.write(doc) } Shame on me, it is very straightforward, should have done it myself. Then I wanted to check what ruby magic the File class' methods offer or if there's any 'simplification' when invoking those methods, so I headed for the documentation here, and checked for the File class. 1.8.6 documentation presents me with "ftools.rb: Extra tools for the File class" under 'File' class, which is not what I'm looking for. 1.8.7 documentation seems OK for 'File' class, there are a plethora of methods. Except 'open'. 1.9 documentation finally shows me the 'open' method. And I had an almost same tour with Net::HTTP. Do I exaggerate when I think good old Turbo Pascal's 7.0 documentation was better organized than Ruby documentation is right now? Is there any other source for the uninitiated to collect knowledge? Or is it possible that I just tumbled into a documentation hole and the rest are super-brilliant-five-star organized? Thanks

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  • Set service dependencies after install

    - by Dennis
    I have an application that runs as a Windows service. It stores various things settings in a database that are looked up when the service starts. I built the service to support various types of databases (SQL Server, Oracle, MySQL, etc). Often times end users choose to configure the software to use SQL Server (they can simply modify a config file with the connection string and restart the service). The problem is that when their machine boots up, often times SQL Server is started after my service so my service errors out on start up because it can't connect to the database. I know that I can specify dependencies for my service to help guide the Windows service manager to start the appropriate services before mine. However, I don't know what services to depend upon at install time (when my service is registered) since the user can change databases later on. So my question is: is there a way for the user to manually indicate the service dependencies based on the database that they are using? If not, what is the proper design approach that I should be taking? I've thought about trying to do something like wait 30 seconds after my service starts up before connecting to the database but this seems really flaky for various reasons. I've also considered trying to "lazily" connect to the database; the problem is that I need a connection immediately upon start up since the database contains various pieces of vital info that my service needs when it first starts. Any ideas?

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  • jQuery Grouping Similar Items and Counting When Repeated

    - by NessDan
    So I have this structure setup: <ul> <li>http://www.youtube.com/watch?v=dw1Vh9Yzryo</li> (Vid1) <li>http://www.youtube.com/watch?v=bOF3o8B292U</li> (Vid2) <li>http://www.youtube.com/watch?v=yAY4vNJd7A8</li> (Vid3) <li>http://www.youtube.com/watch?v=yAY4vNJd7A8</li> <li>http://www.youtube.com/watch?v=dw1Vh9Yzryo</li> <li>http://www.youtube.com/watch?v=bOF3o8B292U</li> <li>http://www.youtube.com/watch?v=yAY4vNJd7A8</li> <li>http://www.youtube.com/watch?v=dw1Vh9Yzryo</li> </ul> Vid1 is repeated 3 times, Vid2 is repeated 3 times, and Vid3 is repeated 2 times. I want to put them into a structure where I can reference them like this: Vid1 - 3 (Repeated), http://www.youtube.com/get_video?video_id=dw1Vh9Yzryo&fmt=36 (Download) Vid2 - 3 (Repeated), http://www.youtube.com/get_video?video_id=bOF3o8B292U&fmt=36 (Download) Vid3 - 2 (Repeated), http://www.youtube.com/get_video?video_id=yAY4vNJd7A8&fmt=36 (Download) "This video was repeated " + [Vid1][Repeated] + " times and you can download it here: " + [Vid1][Download]; How can I set this structure up? I think I should be using an array to achieve the above but I'm not sure how I would set it up or how to reference certain things in the array. The other question is how can I get how many times something was repeated? The URL I have no problem with. Can anyone help me out?

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  • Getting list of Facebook friends with latest API

    - by Eric
    I'm using the most recent version of the Facebook SDK (which lets to connect to something called the 'graph API' though I'm not sure). I've adapted Facebook's example code to let me connect to Facebook and that works... but I can't get a list of my friends. $friends = $facebook->api('friends.get'); This produces the error message: "Fatal error: Uncaught OAuthException: (#803) Some of the aliases you requested do not exist: friends.get thrown in /mycode/facebook.php on line 543" No clue why that is or what that means. Can someone tell me the right syntax (for the latest Facebook API) to get a list of friends? (I tried "$friends = $facebook-api-friends_get();" and get a different error, "Fatal error: Call to a member function friends_get() on a non-object in /mycode/example.php on line 129".) I can confirm that BEFORE this point in my code, things are fine: I'm connected to Facebook with a valid session and I can get my info and dump it to the screen just... i.e. this code executes perfectly before the failed friends.get call: $session = $facebook->getSession(); if ($session) { $uid = $facebook->getUser(); $me = $facebook->api('/me'); } print_r($me);

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  • Appropriate uses of Monad `fail` vs. MonadPlus `mzero`

    - by jberryman
    This is a question that has come up several times for me in the design code, especially libraries. There seems to be some interest in it so I thought it might make a good community wiki. The fail method in Monad is considered by some to be a wart; a somewhat arbitrary addition to the class that does not come from the original category theory. But of course in the current state of things, many Monad types have logical and useful fail instances. The MonadPlus class is a sub-class of Monad that provides an mzero method which logically encapsulates the idea of failure in a monad. So a library designer who wants to write some monadic code that does some sort of failure handling can choose to make his code use the fail method in Monad or restrict his code to the MonadPlus class, just so that he can feel good about using mzero, even though he doesn't care about the monoidal combining mplus operation at all. Some discussions on this subject are in this wiki page about proposals to reform the MonadPlus class. So I guess I have one specific question: What monad instances, if any, have a natural fail method, but cannot be instances of MonadPlus because they have no logical implementation for mplus? But I'm mostly interested in a discussion about this subject. Thanks! EDIT: One final thought occured to me. I recently learned (even though it's right there in the docs for fail) that monadic "do" notation is desugared in such a way that pattern match failures, as in (x:xs) <- return [] call the monad's fail. It seems like the language designers must have been strongly influenced by the prospect of some automatic failure handling built in to haskell's syntax in their inclusion of fail in Monad.

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  • Why does GLSL's arithmetic functions yield so different results on the iPad than on the simulator?

    - by cheeesus
    I'm currently chasing some bugs in my OpenGL ES 2.0 fragment shader code which is running on iOS devices. The code runs fine in the simulator, but on the iPad it has huge problems and some of the calculations yield vastly different results, I had for example 0.0 on the iPad and 4013.17 on the simulator, so I'm not talking about small differences which could be the result of some rounding errors. One of the things I noticed is that, on the iPad, float1 = pow(float2, 2.0); can yield results which are very different from the results of float1 = float2 * float2; Specifically, when using pow(x, 2.0) on a variable containing a larger negative number like -8, it seemed to return a value which satified the condition if (powResult <= 0.0). Also, the result of both operations (pow(x, 2.0) as well as x*x) yields different results in the simulator than on the iPad. Used floats are mediump, but I get the same stuff with highp. Is there a simple explanation for those differences? I'm narrowing the problem down, but it takes so much time, so maybe someone can help me here with a simple explanation.

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  • Formating a table date field from the Model in Codeigniter

    - by Landitus
    Hi, I', trying to re-format a date from a table in Codeigniter. The Controller is for a blog. I was succesfull when the date conversion happens in the View. I was hoping to convert the date in the Model to have things in order. Here's the date conversion as it happens in the View. This is inside the posts loop: <?php foreach($records as $row) : ?> <?php $fdate = "%d <abbr>%M</abbr> %Y"; $dateConv = mdate($fdate, mysql_to_unix($row->date)); ?> <div class="article section"> <span class="date"><?php echo $dateConv ;?></span> ... Keeps going ... This is the Model: class Novedades_model extends Model { function getAll() { $this->db->order_by('date','desc'); $query = $this->db->get('novedades'); if($query->num_rows() > 0) { foreach ($query->result() as $row) { $data[] = $row; } } return $data; } } How can I convert the date in the Model? Can I access the date key and refactor it?

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  • Field Members vs Method Variables?

    - by Braveyard
    Recently I've been thinking about performance difference between class field members and method variables. What exactly I mean is in the example below : Lets say we have a DataContext object for Linq2SQL class DataLayer { ProductDataContext context = new ProductDataContext(); public IQueryable<Product> GetData() { return context.Where(t=>t.ProductId == 2); } } In the example above, context will be stored in heap and the GetData method variables will be removed from Stack after Method is executed. So lets examine the following example to make a distinction : class DataLayer { public IQueryable<Product> GetData() { ProductDataContext context = new ProductDataContext(); return context.Where(t=>t.ProductId == 2); } } (*1) So okay first thing we know is if we define ProductDataContext instance as a field, we can reach it everywhere in the class which means we don't have to create same object instance all the time. But lets say we are talking about Asp.NET and once the users press submit button the post data is sent to the server and the events are executed and the posted data stored in a database via the method above so it is probable that the same user can send different data after one another.If I know correctly after the page is executed, the finalizers come into play and clear things from memory (from heap) and that means we lose our instance variables from memory as well and after another post, DataContext should be created once again for the new page cycle. So it seems the only benefit of declaring it publicly to the whole class is the just number one text above. Or is there something other? Thanks in advance... (If I told something incorrect please fix me.. )

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  • Cocoa - calling a VIEW method from the CONTROLLER

    - by eemerge
    Hello everyone, Got a little problem i asked about it before but maybe i didnt ask properly. I have a cocoa application, which amongst other things, must do the following task: - load some images from the disk, store them in an array and display them in a custom view. In the Interface Builder i have a CustomView and an OBJECT that points to TexturesController.h The custom view is a custom class, TextureBrowser. Below is the code for the controller and view: TexturesController #import <Cocoa/Cocoa.h> @class TextureBrowser; @interface TexturesController : NSObject { IBOutlet NSTextField *logWindow; IBOutlet TextureBrowser *textureView; NSMutableArray *textureList; } @property textureView; -(IBAction)loadTextures:(id)sender; -(IBAction)showTexturesInfo:(id)sender; @end TextureBrowser @interface TextureBrowser : NSView { NSMutableArray *textures; } @property NSMutableArray *textures; -(void)loadTextureList:(NSMutableArray *)source; @end These are just the headers. Now , what i need to do is: when loadTextures from the TexturesController is called, after i load the images i want to send this data to the view (TextureBrowser), for example, store it in the NSMutableArray *textures. I tried using the -(void)loadTextureList:(NSMutableArray*)source method from the view, but in the TextureController.m i get a warning : No -loadTextureList method found This is how i call the method : [textureView loadTextureList: textureList]; And even if i run it with the warning left there, the array in the view class doesnt get initialised. Maybe im missing something...maybe someone can give a simple example of what i need to do and how to do it (code). Thanks in advance.

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  • Specific Shopping Cart Recommendations

    - by Dean J
    I'm trying to suggest a solution for a friend who owns an existing web shop. The current solution isn't cutting it. The new solution needs to have a few things that look like they're enterprise-only if I go with Magento, and $12k a year for a store with maybe $20k in stock just doesn't work. The site should have items, which have one or more categories. Each category may have a parent category. Items have MSRP, and a discount rate by supplier, brand, and sometimes additional discount by product. When a user buys something, it should automatically setup a shipping label with UPS or USPS, depending on user's choice, and build two invoices; one to go in the box, one to go into records. This is crucial; it's low profit per item, so it needs to minimize labor here. Need to be able to have sales (limited by time), discount codes/coupon codes. Ideally would have private sales and/or members-only rates as well. It needs a payment gateway; Paypal/GCheckout-only isn't going to fly. Must be able to accept Visa/MC. Suggestions? I'm debating just building this myself in Java or PHP, but wanted to point my friend to a reasonable-cost solution that already exists if I can. This all seems pretty straightforward to code, save working with the UPS/USPS/Visa/MC APIs, and doing CSS for it.

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  • NSOutlineView not redrawing

    - by Septih
    Hello, I have an NSOutlineView with checkboxes. I have the checkbox state bound to a node item with the key shouldBeCopied. In the node item I have the getters and setters like so: -(BOOL)shouldBeCopied { if([[self parent] shouldBeCopied]) return YES; return shouldBeCopied; } -(void)setShouldBeCopied:(BOOL)value { shouldBeCopied = value; if(value && [[self children] count] > 0) [[self delegate] reloadData]; } The idea here is that if the parent is checked, so should the children. The problem I'm having is that when I check the parent, it does not update that view of the children if they are already expanded. I can understand that it should not be updated by the bindings because i'm not actually changing the value. But should reloadData not cause the bindings to re-get the value, thus calling -shouldBeCopied for the children? I have tried a few other things such as -setNeedsDisplay and -reloadItem:nil reloadChildren:YES but none work. I've noticed that the display gets refreshed when I swap to xcode and then back again and that's all I want, so how do I get it to behave that way?

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  • Inheritance and type parameters of Traversable

    - by Jesper
    I'm studying the source code of the Scala 2.8 collection classes. I have questions about the hierarchy of scala.collection.Traversable. Look at the following declarations: package scala.collection trait Traversable[+A] extends TraversableLike[A, Traversable[A]] with GenericTraversableTemplate[A, Traversable] trait TraversableLike[+A, +Repr] extends HasNewBuilder[A, Repr] with TraversableOnce[A] package scala.collection.generic trait HasNewBuilder[+A, +Repr] trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] extends HasNewBuilder[A, CC[A] @uncheckedVariance] Question: Why does Traversable extend GenericTraversableTemplate with type parameters [A, Traversable] - why not [A, Traversable[A]]? I tried some experimenting with a small program with the same structure and got a strange error message when I tried to change it to Traversable[A]: error: Traversable[A] takes no type parameters, expected: one I guess that the use of the @uncheckedVariance annotation in GenericTraversableTemplate also has to do with this? (That seems like a kind of potentially unsafe hack to force things to work...). Question: When you look at the hierarchy, you see that Traversable inherits HasNewBuilder twice (once via TraversableLike and once via GenericTraversableTemplate), but with slightly different type parameters. How does this work exactly? Why don't the different type parameters cause an error?

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  • Which class should store the lookup table?

    - by max
    The world contains agents at different locations, with only a single agent at any location. Each agent knows where he's at, but I also need to quickly check if there's an agent at a given location. Hence, I also maintain a map from locations to agents. I have a problem deciding where this map belongs to: class World, class Agent (as a class attribute) or elsewhere. In the following I put the lookup table, agent_locations, in class World. But now agents have to call world.update_agent_location every time they move. This is very annoying; what if I decide later to track other things about the agents, apart from their locations - would I need to add calls back to the world object all across the Agent code? class World: def __init__(self, n_agents): # ... self.agents = {} self.agent_locations = {} for id in range(n_agents): x, y = self.find_location() agent = Agent(self,x,y) self.agents.append(agent) self.agent_locations[x,y] = agent def update_agent_location(self, agent, x, y): del self.agent_locations[agent.x, agent.y] self.agent_locations[x, y] = agent def update(self): # next step in the simulation for agent in self.agents: agent.update() # next step for this agent # ... class Agent: def __init__(self, world, x, y): self.world = world self.x, self.y = x, y def move(self, x1, y1): self.world.update_agent_location(self, x1, y1) self.x, self.y = x1, y1 def update(): # find a good location that is not occupied and move there for x, y in self.valid_locations(): if not self.location_is_good(x, y): continue if self.world.agent_locations[x, y]: # location occupied continue self.move(x, y) I can instead put agent_locations in class Agent as a class attribute. But that only works when I have a single World object. If I later decide to instantiate multiple World objects, the lookup tables would need to be world-specific. I am sure there's a better solution... EDIT: I added a few lines to the code to show how agent_locations is used. Note that it's only used from inside Agent objects, but I don't know if that would remain the case forever.

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  • MVVM and avoiding Monolithic God object

    - by bufferz
    I am in the completion stage of a large project that has several large components: image acquisition, image processing, data storage, factory I/O (automation project) and several others. Each of these components is reasonably independent, but for the project to run as a whole I need at least one instance of each component. Each component also has a ViewModel and View (WPF) for monitoring status and changing things. My question is the safest, most efficient, and most maintainable method of instantiating all of these objects, subscribing one class to an Event in another, and having a common ViewModel and View for all of this. Would it best if I have a class called God that has a private instance of all of these objects? I've done this in the past and regretted it. Or would it be better if God relied on Singleton instances of these objects to get the ball rolling. Alternatively, should Program.cs (or wherever Main(...) is) instantiate all of these components, and pass them to God as parameters and then let Him (snicker) and His ViewModel deal with the particulars of running this projects. Any other suggestions I would love to hear. Thank you!

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  • Solr : how do i index and search several fields?

    - by sbrattla
    Hi, I've set up my first 'installation' of Solr, where each index (document) represents a musical work (with properties like number (int), title (string), version (string), composers (string) and keywords (string)). I've set the field 'title' as the default search field. However, what do I do when I would like to do a query on all fields? I'd like to give users the opportunity to search in all fields, and as far as I've understood there is at least two options for this: (1) Specify which fields the query should be made against. (2) Set up the Solr configuration with copyfields, so that values added to each of the fields will be copied to a 'catch-all'-like field which can be used for searching. However, in this case, i am uncertain how things would turn out when i take into consideration that the data types are not all the same for the various fields (the various fields will to a lesser og greater degree go through filters, but as copyfield values are taken from their original fields before the values have been run through their original fields' filters, i would have to apply one single filter to all values on the copyfield. This, again, would result in integers being 'filtered' just as strings would). Is this a case where i should use copyfields? At first glance, it seems a bit more 'flexible' to rather just search on all fields. However, maybe there's a cost? All feedback appreciated! Thanks!

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