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• Dynamically showing fields to a Dev Express Grid view on windows form

  - by Bhaskar

  In one of windows application in C# , I am using Dev Express Grid view control to bind some data and display it to user. I have custom business objects with properties defined for this purpose.Then I simple set the DataSource of the grid to the list of my custom business objects. A while ago , there came a requirement which means that the columns to be displayed on to the grid will be dynamic. This means I cannot know at design time which fields I will need to display. I was thinking of abandoning setting the DataSource and populating the grid manually by code. But I think this will cause many of the grid's features not to work properly, for example , grouping the data by drag n drop of fields to the header area etc. Is there any way to tell a grid at runtime to skip certain fields from a list of BO's when databinding to the grid ?

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• Why aren't my coordinates matching my JFrame size?

  - by AsLanFromNarnia

  I want to do some drawing in a JPanel but the enclosing JFrame size doesn't seem to match where I've asked the coordinates to be drawn. In my example code, the JFrame size is set to (700, 700) and the last point is drawn at (600, 600). I would expect this point to be drawn 100 pixels away from the right and bottom edges but it isn't (please see screenshot). Here's the code I'm using: import java.awt.Graphics; import javax.swing.JFrame; import javax.swing.JPanel; public class Scratch extends JPanel { static int frameWidth = 700; static int frameHeight = 700; public static void main(String[] args) { JFrame frame = new JFrame(); frame.setSize(frameWidth, frameHeight); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); Scratch scratch = new Scratch(); frame.getContentPane().add(scratch); frame.setVisible(true); } @Override public void paintComponent(Graphics g) { g.drawRect(100, 100, 1, 1); g.drawString("100", 100, 100); g.drawRect(200, 200, 1, 1); g.drawString("200", 200, 200); g.drawRect(300, 300, 1, 1); g.drawString("300", 300, 300); g.drawRect(400, 400, 1, 1); g.drawString("400", 400, 400); g.drawRect(500, 500, 1, 1); g.drawString("500", 500, 500); g.drawRect(600, 600, 1, 1); g.drawString("600", 600, 600); } }

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• Threads in Java

  - by owca

  I've created simple program to test Threads in Java. I'd like it to print me numbers infinitely, like 123123123123123. Dunno why, but currently it stops after one cycle finishing 213 only. Anyone knows why ? public class Main { int number; public Main(int number){ } public static void main(String[] args) { new Infinite(2).start(); new Infinite(1).start(); new Infinite(3).start(); } } class Infinite extends Thread { static int which=1; static int order=1; int id; int number; Object console = new Object(); public Infinite(int number){ id = which; which++; this.number = number; } @Override public void run(){ while(1==1){ synchronized(console){ if(order == id){ System.out.print(number); order++; if(order >= which){ order = 1; } try{ console.notifyAll(); console.wait(); } catch(Exception e) {} } else { try{ console.notifyAll(); console.wait(); } catch(Exception e) {} } } try{Thread.sleep(0);} catch(Exception e) {} } } }

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• Speeding up templates in GAE-Py by aggregating RPC calls

  - by Sudhir Jonathan

  Here's my problem: class City(Model): name = StringProperty() class Author(Model): name = StringProperty() city = ReferenceProperty(City) class Post(Model): author = ReferenceProperty(Author) content = StringProperty() The code isn't important... its this django template: {% for post in posts %} <div>{{post.content}}</div> <div>by {{post.author.name}} from {{post.author.city.name}}</div> {% endfor %} Now lets say I get the first 100 posts using Post.all().fetch(limit=100), and pass this list to the template - what happens? It makes 200 more datastore gets - 100 to get each author, 100 to get each author's city. This is perfectly understandable, actually, since the post only has a reference to the author, and the author only has a reference to the city. The __get__ accessor on the post.author and author.city objects transparently do a get and pull the data back (See this question). Some ways around this are Use Post.author.get_value_for_datastore(post) to collect the author keys (see the link above), and then do a batch get to get them all - the trouble here is that we need to re-construct a template data object... something which needs extra code and maintenance for each model and handler. Write an accessor, say cached_author, that checks memcache for the author first and returns that - the problem here is that post.cached_author is going to be called 100 times, which could probably mean 100 memcache calls. Hold a static key to object map (and refresh it maybe once in five minutes) if the data doesn't have to be very up to date. The cached_author accessor can then just refer to this map. All these ideas need extra code and maintenance, and they're not very transparent. What if we could do @prefetch def render_template(path, data) template.render(path, data) Turns out we can... hooks and Guido's instrumentation module both prove it. If the @prefetch method wraps a template render by capturing which keys are requested we can (atleast to one level of depth) capture which keys are being requested, return mock objects, and do a batch get on them. This could be repeated for all depth levels, till no new keys are being requested. The final render could intercept the gets and return the objects from a map. This would change a total of 200 gets into 3, transparently and without any extra code. Not to mention greatly cut down the need for memcache and help in situations where memcache can't be used. Trouble is I don't know how to do it (yet). Before I start trying, has anyone else done this? Or does anyone want to help? Or do you see a massive flaw in the plan?

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• Why this code showing error in W3C validator?

  - by metal-gear-solid

  Why this code showing error in W3C validator "character data is not allowed here" <blockquote>all visible objects, man, are but as pasteboard masks. But in each event -- in the living act, the undoubted deed -- there, some unknown but still reasoning thing puts forth the mouldings of its feature from behind the unreasoning mask. If man will strike, strike through the mask. All visible objects, man, are but as pasteboard masks. But in each event -- in the living act, the undoubted deed -- there, some unknown but still reasoning thing puts forth the mouldings of its feature from behind the unreasoning mask. If man will strike, strike through the mask.</blockquote> It does not giving any error in this validator http://www.onlinewebcheck.com/ and not in https://addons.mozilla.org/en-US/firefox/addon/249/

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• Android: Deciding between SurfaceView and OpenGL (GLSurfaceView)

  - by Rich

  Is there a way to decide up front based on the expected complexity of a game/app in the planning phase whether to use regular Canvas drawing in a SurfaceView or to go with OpenGL? I've been playing around with a Canvas and only need 2D movement, and on a fairly new phone I'm getting pretty decent performance with a bunch of primitive objects and a few bitmaps running around the screen on a solid background. Is it fair to say that if I'm going to be drawing background images and increasing the number of objects being moved and drawn on top of them that I should go straight to OpenGL?

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• An Efficient data structure for Sorted List

  - by holydiver

  I want to save my objects according to a key in the attributes of my object in a sorted fashion. Later on I'll access these objects sequentially from max key to min key. I'll do some search tasks as well. I consider to use either AVL tree or RB Tree. As far as i know they are nearly equivalent in theory(Both have O(logn)). But in practice which one might be better in performance in my situation. And is there a better alternative than those, considering that I'll mostly do insert and sequentially access to the ds.

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• How much does Website Development cost nowadays?

  - by Andreas Grech

  I am thinking of setting up my own freelance business but coming from a workplace that offers a particular service to huge clients, I do not know what are the current charges for websites are nowadays. I know that as technology just keeps changing and changing (most of the time, for the better...), the amount you charge for a single website is constantly differing. Like for example, I don't think static websites (with just static html pages) are that expensive today, no? (as i said, I might be mistaken since I haven't really touched on this freelance industry yet) So, freelance web-developers out there, can you give me estimates on how much you charge for your clients? Some examples of websites that I want to know an approx charge: ~10 static html pages ~10 dhtml pages (with maybe a flasy menu on the top/side) Database driven websites with a standard CMS (be it the one you developed, or an existing one) Database driven but with a custom-built cms for the particular client Using an existing template for a design Starting the design from scratch etc... I know that the normally clients don't really care about the technologies used to construct their websites, but do you charge differently according to which technology you use to build the website with?; as in, is the technology a factor when setting the price? ...being ASP.Net, PHP, Ruby On Rails etc... Also, how do you go on about charging your clients for your services? What are the major factors that you consider when setting a price tag for a website to a client ? And better yet, how do you even find prospective clients? <= [or should I leave this question for a different post?] Btw, in your post, also mention some numbers (in cash values, be it in USD, GBP, EUR or anything) because I want to be able to take calculate some averages from this post when some answers stack up

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• Using Doctrine to abstract CRUD operations

  - by TomWilsonFL

  This has bothered me for quite a while, but now it is necessity that I find the answer. We are working on quite a large project using CodeIgniter plus Doctrine. Our application has a front end and also an admin area for the company to check/change/delete data. When we designed the front end, we simply consumed most of the Doctrine code right in the controller: //In semi-pseudocode function register() { $data = get_post_data(); if (count($data) && isValid($data)) { $U = new User(); $U->fromArray($data); $U->save(); $C = new Customer(); $C->fromArray($data); $C->user_id = $U->id; $C->save(); redirect_to_next_step(); } } Obviously when we went to do the admin views code duplication began and considering we were in a "get it DONE" mode so it now stinks with code bloat. I have moved a lot of functionality (business logic) into the model using model methods, but the basic CRUD does not fit there. I was going to attempt to place the CRUD into static methods, i.e. Customer::save($array) [would perform both insert and update depending on if prikey is present in array], Customer::delete($id), Customer::getObj($id = false) [if false, get all data]. This is going to become painful though for 32 model objects (and growing). Also, at times models need to interact (as the interaction above between user data and customer data), which can't be done in a static method without breaking encapsulation. I envision adding another layer to this (exposing web services), so knowing there are going to be 3 "controllers" at some point I need to encapsulate this CRUD somewhere (obviously), but are static methods the way to go, or is there another road? Your input is much appreciated.

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• C# app running as either Windows Form or as Console Application

  - by Aeolien

  I am looking to have one of my Windows Forms applications be run programmatically—from the command line. In preparation, I have separated the logic in its own class from the Form. Now I am stuck trying to get the application to switch back and forth based on the presence of command line arguments. Here is the code for the main class: static class Program { /// <summary> /// The main entry point for the application. /// </summary> [STAThread] static void Main() { string[] args = Environment.GetCommandLineArgs(); if (args.Length > 1) // gets passed its path, by default { CommandLineWork(args); return; } Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(new Form1()); } private static void CommandLineWork(string[] args) { Console.WriteLine("It works!"); Console.ReadLine(); } where Form1 is my form and the It works! string is just a placeholder for the actual logic. Right now, when running this from within Visual Studio (with command line arguments), the phrase It works! is printed to the Output. However, when running the /bin/Debug/Program.exe file (or /Release for that matter) the application crashes. Am I going about this the right way? Would it make more sense (i.e. take less developer time) to have my logic class be a DLL that gets loaded by two separate applications? Or is there something entirely different that I'm not aware of? Thanks in advance!

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• How to build boost foreach cycle

  - by Ockonal

  Hi guys! I have some abstract class called IClass (has pure virtual function). There are some classes which inherit IClass: CFirst, CSecond. I want to add objects of classes which inherit into boost::ptr_vector: class IClass { virtual void someFunc() = 0; }; class CFirst : public IClass { }; class CSecond : public IClass { }; boost::ptr_vector<IClass> objectsList; objectsList.push_back(new CFirst()); objectsList.push_back(new CSecond()); And now my goal is to call function (which is declarated in IClass) from all objects in objectsList. I'd prefer to use BOOST_FOREACH: foreach(IClass tempObj, objectsList) { tempObj.someFunc(); } The problem is that IClass - abstract class, so I can't make instance of it for the foreach-cycle. What should I do?

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• Java map with values limited by key's type parameter

  - by Ashley Mercer

  Is there a way in Java to have a map where the type parameter of a value is tied to the type parameter of a key? What I want to write is something like the following: public class Foo { // This declaration won't compile - what should it be? private static Map<Class<T>, T> defaultValues; // These two methods are just fine public static <T> void setDefaultValue(Class<T> clazz, T value) { defaultValues.put(clazz, value); } public static <T> T getDefaultValue(Class<T> clazz) { return defaultValues.get(clazz); } } That is, I can store any default value against a Class object, provided the value's type matches that of the Class object. I don't see why this shouldn't be allowed since I can ensure when setting/getting values that the types are correct. EDIT: Thanks to cletus for his answer. I don't actually need the type parameters on the map itself since I can ensure consistency in the methods which get/set values, even if it means using some slightly ugly casts.

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• Advice on Method overloads.

  - by Muhammad Kashif Nadeem

  Please see following methods. public static ProductsCollection GetDummyData(int? customerId, int? supplierId) { try { if (customerId != null && customerId > 0) { Filter.Add(Customres.CustomerId == customerId); } if (supplierId != null && supplierId > 0) { Filter.Add(Suppliers.SupplierId == supplierId); } ProductsCollection products = new ProductsCollection(); products.FetchData(Filter); return products; } catch { throw; } } public static ProductsCollection GetDummyData(int? customerId) { return ProductsCollection GetDummyData(customerId, (int?)null); } public static ProductsCollection GetDummyData() { return ProductsCollection GetDummyData((int?)null); } 1- Please advice how can I make overloads for both CustomerId and SupplierId because only one overload can be created with GetDummyData(int? ). Should I add another argument to mention that first argument is CustomerId or SupplierId for example GetDummyData(int?, string). OR should I use enum as 2nd argument and mention that first argument is CustoemId or SupplierId. 2- Is this condition is correct or just checking 0 is sufficient - if (customerId != null && customerId 0) 3- Using Try/catch like this is correct? 4- Passing (int?)null is correct or any other better approach. Edit: I have found some other posts like this and because I have no knowledge of Generics that is why I am facing this problem. Am I right? Following is the post. http://stackoverflow.com/questions/422625/overloaded-method-calling-overloaded-method

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• "Unable to find any mappings for the given content, keyPath=null" RestKit 0.2

  - by abisson

  So I switched to using RestKit 0.2 and CoreData and I've been having a lot of trouble trying to get the mappings correct... I don't understand why. The JSON Response of my server is like this: { "meta": { "limit": 20, "next": null, "offset": 0, "previous": null, "total_count": 2 }, "objects": [{ "creation_date": "2012-10-15T20:16:47", "description": "", "id": 1, "last_modified": "2012-10-15T20:16:47", "order": 1, "other_names": "", "primary_name": "Mixing", "production_line": "/api/rest/productionlines/1/", "resource_uri": "/api/rest/cells/1/" }, { "creation_date": "2012-10-15T20:16:47", "description": "", "id": 2, "last_modified": "2012-10-15T20:16:47", "order": 2, "other_names": "", "primary_name": "Packaging", "production_line": "/api/rest/productionlines/1/", "resource_uri": "/api/rest/cells/2/" }] } Then in XCode I have: RKObjectManager *objectManager = [RKObjectManager sharedManager]; [AFNetworkActivityIndicatorManager sharedManager].enabled = YES; NSManagedObjectModel *managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil]; RKManagedObjectStore *managedObjectStore = [[RKManagedObjectStore alloc] initWithManagedObjectModel:managedObjectModel]; objectManager.managedObjectStore = managedObjectStore; RKEntityMapping *cellMapping = [RKEntityMapping mappingForEntityForName:@"Cell" inManagedObjectStore:managedObjectStore]; cellMapping.primaryKeyAttribute = @"identifier"; [cellMapping addAttributeMappingsFromDictionary:@{ @"id": @"identifier", @"primary_name": @"primaryName", }]; RKResponseDescriptor *responseCell = [RKResponseDescriptor responseDescriptorWithMapping:cellMapping pathPattern:@"/api/rest/cells/?format=json" keyPath:@"objects" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)]; [objectManager addResponseDescriptorsFromArray:@[responseCell, responseUser, responseCompany]]; [managedObjectStore createPersistentStoreCoordinator]; NSString *storePath = [RKApplicationDataDirectory() stringByAppendingPathComponent:@"AppDB.sqlite"]; NSString *seedPath = [[NSBundle mainBundle] pathForResource:@"SeedDatabase" ofType:@"sqlite"]; NSError *error; NSPersistentStore *persistentStore = [managedObjectStore addSQLitePersistentStoreAtPath:storePath fromSeedDatabaseAtPath:seedPath withConfiguration:nil options:nil error:&error]; NSAssert(persistentStore, @"Failed to add persistent store with error: %@", error); // Create the managed object contexts [managedObjectStore createManagedObjectContexts]; // Configure a managed object cache to ensure we do not create duplicate objects managedObjectStore.managedObjectCache = [[RKInMemoryManagedObjectCache alloc] initWithManagedObjectContext:managedObjectStore.persistentStoreManagedObjectContext]; My request is: [[RKObjectManager sharedManager] getObjectsAtPath:@"/api/rest/cells/?format=json" parameters:nil success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) { RKLogInfo(@"Load complete: Table should refresh..."); [[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:@"LastUpdatedAt"]; [[NSUserDefaults standardUserDefaults] synchronize]; } failure:^(RKObjectRequestOperation *operation, NSError *error) { RKLogError(@"Load failed with error: %@", error); }]; And I always get the following error: **Error Domain=org.restkit.RestKit.ErrorDomain Code=1001 "Unable to find any mappings for the given content" UserInfo=0x1102d500 {DetailedErrors=(), NSLocalizedDescription=Unable to find any mappings for the given content, keyPath=null}** Thanks a lot!

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• How do you deal with the conflict between ActiveSupport::JSON and the JSON gem?

  - by Luke Francl

  I am stumped with this problem. ActiveSupport::JSON defines to_json on various core objects and so does the JSON gem. However, the implementation is not the same -- the ActiveSupport version takes arguments and the JSON gem version doesn't. I installed a gem that required the JSON gem and my app broke. The issue is that I'm using to_json in a controller that returns a list of objects, but I want to control which attributes are returned. When code anywhere in my system does require 'json' I get this error message: TypeError: wrong argument type Hash (expected Data) I tried a couple of things that I read online to fix it, but nothing worked. I ended up re-writing the gem to use ActiveSupport::JSON.decode instead of JSON.parse. This works but it's not sustainable...I can't be forking gems every time I want to use a gem that requires the JSON gem. Update: The best solution of this problem is to upgrade to Rails 2.3 or higher, which fixed it.

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• Recommendations for an in memory database vs thread safe data structures

  - by yx

  TLDR: What are the pros/cons of using an in-memory database vs locks and concurrent data structures? I am currently working on an application that has many (possibly remote) displays that collect live data from multiple data sources and renders them on screen in real time. One of the other developers have suggested the use of an in memory database instead of doing it the standard way our other systems behaves, which is to use concurrent hashmaps, queues, arrays, and other objects to store the graphical objects and handling them safely with locks if necessary. His argument is that the DB will lessen the need to worry about concurrency since it will handle read/write locks automatically, and also the DB will offer an easier way to structure the data into as many tables as we need instead of having create hashmaps of hashmaps of lists, etc and keeping track of it all. I do not have much DB experience myself so I am asking fellow SO users what experiences they have had and what are the pros & cons of inserting the DB into the system?

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• django left join with null

  - by SledgehammerPL

  The model: class Product(models.Model): name = models.CharField(max_length = 128) def __unicode__(self): return self.name class Receipt(models.Model): name = models.CharField(max_length=128) components = models.ManyToManyField(Product, through='ReceiptComponent') class Admin: pass def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive The idea: there are a components on stock. I'd like to find out which recipes I can made with components which I have. It's not easy - but possible - I made a SQL view, which gets the solution. But I'm learning python and Django so I'd like to make it Django-style ;D The concept of solution: get the set of recipes which has at last one component: list_of_available_components = ReceiptComponent.objects.filter(product__in=list_of_available_products).distinct() list_of_related_receipts = Receipt.objects.filter(receiptcomponent__in = list_of_available_components).distinct() get recipes (from list_of_related_receipts) which has not at last one component list_of_incomplete_recipes = (SELECT * FROM drinkbook_receiptcomponent LEFT JOIN drinkstore_stock_products USING(product_id) WHERE drinkstore_stock_products.stock_id IS NULL AND receipt_id IN (SELECT receipt_id FROM drinkbook_receiptcomponent JOIN drinkstore_stock_products USING(product_id))) get recipes (from list_of_related_receipts) which are not in "list_of_incomplete_recipes"

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• Scheme: what are the benefits of letrec?

  - by Ixmatus

  While reading "The Seasoned Schemer" I've begun to learn about letrec. I understand what it does (can be duplicated with a Y-Combinator) but the book is using it in lieu of recurring on the already defined function operating on arguments that remain static. An example of an old function using the defined function recurring on itself (nothing special): (define (substitute new old lat) (cond ((null? l) '()) ((eq? (car l) old) (cons new (substitute new old (cdr l)))) (else (cons (car l) (substitute new old (cdr l)))))) Now for an example of that same function but using letrec: (define (substitute new old lat) (letrec ((replace (lambda (l) (cond ((null? l) '()) ((eq? (car l) old) (cons new (replace (cdr l)))) (else (cons (car l) (replace (cdr l)))))))) (replace lat))) Aside from being slightly longer and more difficult to read I don't know why they are rewriting functions in the book to use letrec. Is there a speed enhancement when recurring over a static variable this way because you don't keep passing it?? Is this standard practice for functions with arguments that remain static but one argument that is reduced (such as recurring down the elements of a list)? Some input from more experienced Schemers/LISPers would help!

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• to connect matlab with java

  - by user304005

  Through the below given code I was able to connect to matlab. But I was not able to execute the script file containing matlab code...Please help me to modify the code so as to execute the matlab code.... Here luck2 is a .m file.... import java.io.InputStreamReader; import java.io.*; public class matlab { private static File myMATLABScript; public static String runScript(File luck2) { String output = "" ; String error = ""; try { String commandToRun ="C:\\Program Files\\MATLAB\\R2009a\\bin\\matlab -nodisplay <" + "Z:\\sem\\java\\luck2"; //String commandToRun = "matlab -nosplash -r myMATLABScript -nodisplay -nodesktop < " + opentxt; System.out.println(commandToRun); Process p = Runtime.getRuntime().exec(commandToRun); String s; BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream())); BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream())); System.out.println("\nHere is the standard output of the command:\n"); while ((s = stdInput.readLine()) != null) { System.out.println("haiiiiiiiiiiii"); output = s + "\n"; System.out.println(s); } while ((s = stdError.readLine()) != null) { error = s + "\n"; System.out.println(s); } } catch (Exception e) { System.out.println("exception happened here what I know:"); e.printStackTrace(); System.exit(-1); } return output + error; } public static void main(String[] args) throws IOException { matlab m = new matlab(); matlab.runScript(myMATLABScript); //matlab.runScript(); } }

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• How to deal with many to many relationships with NSFetchedResultsController?

  - by Phil Yates

  OK so I have two entities in my data model (let's say entityA and entityB), both of these entities have a to-many relationship to each other. I have setup a NSFetchedResultsController to fetch a bunch of entityA. Now I'm trying to have the section names for the tableview be the title of entityB. sectionNameKeyPath:@"entityB.title" Now this causes a problem, where by the section name returned from that relationship appears to be ({title1}) or ({title1,title2...titleN}) obviously depending on how many different entityB's are involved. This doesn't look great in a tableview and doesn't group the objects as I would like. What I would like is a section per entityB title with entityA appearing under each section, under multiple sections if necessary. I'm at a loss as how I am supposed to achieve this whether I need to update the predicate to get the entity to appear multiple times or whether I need to update the section and header functions to do some processing as the controller loops through the objects. Any help is appreciated :) Thanks

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• In Java it seems Public constructors are always a bad coding practice

  - by Adam Gent

  This maybe a controversial question and may not be suited for this forum (so I will not be insulted if you choose to close this question). It seems given the current capabilities of Java there is no reason to make constructors public ... ever. Friendly, private, protected are OK but public no. It seems that its almost always a better idea to provide a public static method for creating objects. Every Java Bean serialization technology (JAXB, Jackson, Spring etc...) can call a protected or private no-arg constructor. My questions are: I have never seen this practice decreed or written down anywhere? Maybe Bloch mentions it but I don't own is book. Is there a use case other than perhaps not being super DRY that I missed? EDIT: I explain why static methods are better. .1. For one you get better type inference. For example See Guava's http://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained .2. As a designer of the class you can later change what is returned with a static method. .3. Dealing with constructor inheritance is painful especially if you have to pre-calculate something.

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• Why is django admin not accepting Nullable foreign keys?

  - by p.g.l.hall

  Here is a simplified version of one of my models: class ImportRule(models.Model): feed = models.ForeignKey(Feed) name = models.CharField(max_length=255) feed_provider_category = models.ForeignKey(FeedProviderCategory, null=True) target_subcategories = models.ManyToManyField(Subcategory) This class manages a rule for importing a list of items from a feed into the database. The admin system won't let me add an ImportRule without selecting a feed_provider_category despite it being declared in the model as nullable. The database (SQLite at the moment) even checks out ok: >>> .schema ... CREATE TABLE "someapp_importrule" ( "id" integer NOT NULL PRIMARY KEY, "feed_id" integer NOT NULL REFERENCES "someapp_feed" ("id"), "name" varchar(255) NOT NULL, "feed_provider_category_id" integer REFERENCES "someapp_feedprovidercategory" ("id"), ); ... I can create the object in the python shell easily enough: f = Feed.objects.get(pk=1) i = ImportRule(name='test', feed=f) i.save() ...but the admin system won't let me edit it, of course. How can I get the admin to let me edit/create objects without specifying that foreign key?

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• Enumerable Contains Enumerable

  - by Tim

  For a method I have the following parameter IEnumerable<string> tags and with to query a list of objects, let's call them Post, that contains a property IEnumerable<string> Tags { get; set; }. My question is: How do I use linq to query for objects that contains all the tags from the tags parameter? private List<Post> posts = new List<Post>(); public IEnumerable<Post> GetPostsWithTags(IEnumerable<string> tags) { return ???; }

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• Factory Method pattern and public constructor

  - by H4mm3rHead

  Hi, Im making a factory method that returns new instances of my objects. I would like to prevent anyone using my code from using a public constructor on my objects. Is there any way of doing this? How is this typically accomplished: public abstract class CarFactory { public abstract ICar CreateSUV(); } public class MercedesFactory : CarFactory { public override ICar CreateSUV() { return new Mercedes4WD(); } } I then would like to limit/prevent the other developers (including me in a few months) from making an instance of Mercedes4WD. But make them call my factory method. How to?

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• What is a flexible, hybrid python collection object?

  - by Naveen

  As a way to get used to python, I am trying to translate some of my code to python from Autohotkey_L. I am immediately running into tons of choices for collection objects. Can you help me figure out a built in type or a 3rd party contributed type that has as much as possible, the functionality of the AutoHotkey_L object type and its methods. AutoHotkey_L Objects have features of a python dict, list, and a class instance. I understand that there are tradeoffs for space and speed, but I am just interested in functionality rather than optimization issues.

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