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  • DTO or Domain Model Object in the View Layer?

    - by smayers81
    I know this is probably an age-old question, but what is the better practice? Using a domain model object throughout all layers of your application, and even binding values directly to them on the JSP (I'm using JSF). Or convert a domain model object into a DTO in the DAO or Service layer and send a lightweight DTO to the presentation layer. I have been told it makes no sense to use DTOs because changes to the database will result in changes to all your DTOs whereas using Model Objects everywhere will just require changes to the affected model object. However, the ease of use and the lightweight nature of DTOs seems to outweigh that. I should note that my app uses Hibernate Model Objects AND uses its own custom-created model objects (meaning not bound to any DB session, always detached). Is either of the above scenarios more beneficial to a strict Model Object pattern? Using Hibernate has been a huge PITA with regards to things like Lazy Initialization Exceptions.

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  • Objects not loading on second request in Restkit

    - by Holger Edward Wardlow Sindbæk
    I'm sending off 2 requests simultaneously with Restkit and I receive a response back from both of them, but only one of the requests receives any objects. If I send them off one by one, then my objectloader receives all objects. First request: self.firstObjectManager = [RKObjectManager sharedManager]; [self.firstObjectManager loadObjectsAtResourcePath:[NSString stringWithFormat: @"/%@.json", subUrl] usingBlock:^(RKObjectLoader *loader){ [loader.mappingProvider setObjectMapping:designArrayMapping forKeyPath:@""]; loader.userData = @"design"; loader.delegate = self; [loader sendAsynchronously]; }]; Second request: self.secondObjectManager = [RKObjectManager sharedManager]; [self.secondObjectManager loadObjectsAtResourcePath:[NSString stringWithFormat: @"/%@.json", subUrl] usingBlock:^(RKObjectLoader *loader){ [loader.mappingProvider setObjectMapping:designerMapping forKeyPath:@""]; loader.userData = @"designer"; loader.delegate = self; [loader sendAsynchronously]; }]; My objecloader: -(void)objectLoader:(RKObjectLoader *)objectLoader didLoadObjects:(NSArray *)objects { //NSLog(@"This happened: %@", objectLoader.userData); if (objectLoader.userData == @"design") { NSLog(@"Design happened: %i", objects.count); }else if(objectLoader.userData == @"designer"){ NSLog(@"designer: %@", [objects objectAtIndex:0]); } } My response: 2012-11-18 14:36:19.607 RestKitTest5[14220:c07] Started loading of request: designer 2012-11-18 14:36:22.575 RestKitTest5[14220:c07] I restkit.network:RKRequest.m:680:-[RKRequest updateInternalCacheDate] Updating cache date for request <RKObjectLoader: 0x95c3160> to 2012-11-18 19:36:22 +0000 2012-11-18 14:36:22.576 RestKitTest5[14220:c07] response code: 200 2012-11-18 14:36:22.584 RestKitTest5[14220:c07] Design happened: 0 2012-11-18 14:36:22.603 RestKitTest5[14220:c07] I restkit.network:RKRequest.m:680:-[RKRequest updateInternalCacheDate] Updating cache date for request <RKObjectLoader: 0xa589b50> to 2012-11-18 19:36:22 +0000 2012-11-18 14:36:22.605 RestKitTest5[14220:c07] response code: 200 2012-11-18 14:36:22.606 RestKitTest5[14220:c07] designer: <DesignerData: 0xa269fc0> Update: Setting my base url RKURL *baseURL = [RKURL URLWithBaseURLString:@"http://iphone.meer.li"]; [RKObjectManager setSharedManager:[RKObjectManager managerWithBaseURL:baseURL]]; Solution Problem was that I used the shared manager for both object managers, so I ended up doing: RKURL *baseURL = [RKURL URLWithBaseURLString:@"http://iphone.meer.li"]; RKObjectManager *myObjectManager = [[RKObjectManager alloc] initWithBaseURL:baseURL]; self.firstObjectManager = myObjectManager; and: RKURL *baseURL = [RKURL URLWithBaseURLString:@"http://iphone.meer.li"]; RKObjectManager *myObjectManager = [[RKObjectManager alloc] initWithBaseURL:baseURL]; self.secondObjectManager = myObjectManager;

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  • Creating my own SAP dashboard/reporting tool for mobile

    - by novwareman
    Hi! Is it possible to create my own mobile dashboard, reporting tool for SAP? I understand the standard components to be used for this purpose are: Business Objects Enterprise Server XI - this provides reporting functionalities for SAP Business Objects Mobile Server - this connects to Enterprise Server and optimizes reports stored there for mobile devices Mobile Web Browser or Mobile Business Objects Report Client - for viewing the reports I don't intend to purchase the components mentioned above. I only want to know if it's feasible to build my own solution. I am familiar with BAPI's to retrieve data from SAP. What is the proper approach to build an SAP reporting tool? Thank you!

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  • django blog - post- reply system display replies

    - by dana
    I have a mini blog app, and a reply system. I want to list all mini blog entries, and their replies, if there are any. i have in views.py def profile_view(request, id): u = UserProfile.objects.get(pk=id) paginator = New.objects.filter(created_by = request.user) replies = Reply.objects.filter(reply_to = paginator) return render_to_response('profile/publicProfile.html', { 'object_list': u, 'list':paginator, 'replies':replies }, context_instance=RequestContext(request)) and in the template: <h3>Recent Entries:</h3> {% for object in list %} <li>{{ object.post }} <br /> {% for object in replies %} {{ object.reply }} <br /> {% endfor %} mention : reply_to is a ForeignKey to New, and New is the name of the 'mini blog' table But it only shows all the replies for each blog entry, not the reply for every entry, if there is one thanks

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  • C# Different class objects in one list

    - by jeah_wicer
    I have looked around some now to find a solution to this problem. I found several ways that could solve it but to be honest I didn't realize which of the ways that would be considered the "right" C# or OOP way of solving it. My goal is not only to solve the problems but also to develop a good set of code standards and I'm fairly sure there's a standard way to handle this problem. Let's say I have 2 types of printer hardwares with their respective classes and ways of communicating: PrinterType1, PrinterType2. I would also like to be able to later on add another type if neccessary. One step up in abstraction those have much in common. It should be possible to send a string to each one of them as an example. They both have variables in common and variables unique to each class. (One for instance communicates via COM-port and has such an object, while the other one communicates via TCP and has such an object). I would however like to just implement a List of all those printers and be able to go through the list and perform things as "Send(string message)" on all Printers regardless of type. I would also like to access variables like "PrinterList[0].Name" that are the same for both objects, however I would also at some places like to access data that is specific to the object itself (For instance in the settings window of the application where the COM-port name is set for one object and the IP/port number for another). So, in short something like: In common: Name Send() Specific to PrinterType1: Port Specific to PrinterType2: IP And I wish to, for instance, do Send() on all objects regardless of type and the number of objects present. I've read about polymorphism, Generics, interfaces and such, but I would like to know how this, in my eyes basic, problem typically would be dealt with in C# (and/or OOP in general). I actually did try to make a base class, but it didn't quite seem right to me. For instance I have no use of a "string Send(string Message)" function in the base class itself. So why would I define one there that needs to be overridden in the derived classes when I would never use the function in the base class ever in the first place? I'm really thankful for any answers. People around here seem very knowledgeable and this place has provided me with many solutions earlier. Now I finally have an account to answer and vote with too. EDIT: To additionally explain, I would also like to be able to access the objects of the actual printertype. For instance the Port variable in PrinterType1 which is a SerialPort object. I would like to access it like: PrinterList[0].Port.Open() and have access to the full range of functionality of the underlaying port. At the same time I would like to call generic functions that work in the same way for the different objects (but with different implementations): foreach (printer in Printers) printer.Send(message)

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  • ASP.NET MVC: what mechanic returns ViewModel objects?

    - by Dr. Zim
    As I understand it, Domain Models are classes that only describe the data (aggregate roots). They are POCOs and do not reference outside libraries (nothing special). View models on the other hand are classes that contain domain model objects as well as all the interface specific objects like SelectList. A ViewModel includes using System.Web.Mvc;. A repository pulls data out of a database and feeds them to us through domain model objects. What mechanic or device creates the view model objects, populating them from a database? Would it be a factory that has database access? Would you bleed the view specific classes like System.Web.Mvc in to the Repository? Something else? For example, if you have a drop down list of cities, you would reference a SelectList object in the root of your View Model object, right next to your DomainModel reference: public class CustomerForm { public CustomerAddress address {get;set;} public SelectList cities {get;set;} } The cities should come from a database and be in the form of a select list object. The hope is that you don't create a special Repository method to extract out just the distinct cities, then create a redundant second SelectList object only so you have the right data types.

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  • Problem with writeToFile with array of NSDictionary objects

    - by Ken
    I'm trying to write an array of NSDictionary objects to a .plist file on the iPhone (OS 3.0). (They are actually NSCFDictionary objects when I call the [object class] method). My problem is that it won't write to file. If I set the array to "nil" it at least creates the empty plist file but won't do it if I have these objects in the array. My array is a parsed response from a JSON HTTP request and looks like this: { "title" = "A Movie"; "time_length" = "3:22"; }, { "title" = "Another Movie"; "time_length" = "1:40"; }, { "title" = "A Third Movie"; "time_length" = "2:10"; } The code to create the file is: [array writeToFile:[self dataFilePath] atomically:YES]; - (NSString *)dataFilePath { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; return [documentsDirectory stringByAppendingPathComponent:@"data.plist"]; } Could the NCSFDictionary class of the objects in my array be preventing me from writing to file? Thanks for your help.

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  • Batch faulting in a to-many relationship for a collection of objects

    - by indragie
    Scenario: Let's say I have an entity called Author that has a to-many relationship called books to the Book entity (inverse relationship author). If I have an existing collection of Author objects, I want to fault in the books relationship for all of them in a single fetch request. Code This is what I've tried so far: NSArray *authors = ... // array of `Author` objects NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Book"]; fetchRequest.returnsObjectsAsFaults = NO; fetchRequest.predicate = [NSPredicate predicateWithFormat:@"author IN %@", authors]; Executing this fetch request does not result in the books relationship of the objects in the authors array being faulted in (inspected via logging). I've also tried doing the fetch request the other way around: NSArray *authors = ... // array of `Author` objects NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Author"]; fetchRequest.returnsObjectsAsFaults = NO; fetchRequest.predicate = [NSPredicate predicateWithFormat:@"SELF IN %@", authors]; fetchRequest.relationshipKeypathsForPrefetching = @[@"books"]; This doesn't fire the faults either. What's the appropriate way of going about doing this?

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  • The fastest way to iterate through a collection of objects

    - by Trev
    Hello all, First to give you some background: I have some research code which performs a Monte Carlo simulation, essential what happens is I iterate through a collection of objects, compute a number of vectors from their surface then for each vector I iterate through the collection of objects again to see if the vector hits another object (similar to ray tracing). The pseudo code would look something like this for each object { for a number of vectors { do some computations for each object { check if vector intersects } } } As the number of objects can be quite large and the amount of rays is even larger I thought it would be wise to optimise how I iterate through the collection of objects. I created some test code which tests arrays, lists and vectors and for my first test cases found that vectors iterators were around twice as fast as arrays however when I implemented a vector in my code in was somewhat slower than the array I was using before. So I went back to the test code and increased the complexity of the object function each loop was calling (a dummy function equivalent to 'check if vector intersects') and I found that when the complexity of the function increases the execution time gap between arrays and vectors reduces until eventually the array was quicker. Does anyone know why this occurs? It seems strange that execution time inside the loop should effect the outer loop run time.

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  • Avoid loading unnecessary data from db into objects (web pages)

    - by GmGr
    Really newbie question coming up. Is there a standard (or good) way to deal with not needing all of the information that a database table contains loaded into every associated object. I'm thinking in the context of web pages where you're only going to use the objects to build a single page rather than an application with longer lived objects. For example, lets say you have an Article table containing id, title, author, date, summary and fullContents fields. You don't need the fullContents to be loaded into the associated objects if you're just showing a page containing a list of articles with their summaries. On the other hand if you're displaying a specific article you might want every field loaded for that one article and maybe just the titles for the other articles (e.g. for display in a recent articles sidebar). Some techniques I can think of: Don't worry about it, just load everything from the database every time. Have several different, possibly inherited, classes for each table and create the appropriate one for the situation (e.g. SummaryArticle, FullArticle). Use one class but set unused properties to null at creation if that field is not needed and be careful. Give the objects access to the database so they can load some fields on demand. Something else? All of the above seem to have fairly major disadvantages. I'm fairly new to programming, very new to OOP and totally new to databases so I might be completely missing the obvious answer here. :)

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  • XML/RDF to Java Objects with XSD

    - by bmucklow
    So here's the scenario...I have an XSD file describing all the objects that I need. I can create the objects in Java using JAXB no problem. I have an XML/RDF file that I need to parse into those objects. What is the EASIEST way to do this? I have been looking into Jena and have played around with it, but can't see how to easily map the XML/RDF file to the XSD objects that were generated. Here is a snippet of the XSD file as well as the XML/RDF file: <?xml version="1.0" encoding="UTF-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:a="http://langdale.com.au/2005/Message#" xmlns:sawsdl="http://www.w3.org/ns/sawsdl" targetNamespace="http://iec.ch/TC57/2007/profile#" elementFormDefault="qualified" attributeFormDefault="unqualified" xmlns="http://langdale.com.au/2005/Message#" xmlns:m="http://iec.ch/TC57/2007/profile#"> <xs:annotation/> <xs:element name="Profile" type="m:Profile"/> <xs:complexType name="Profile"> <xs:sequence> <xs:element name="Breaker" type="m:Breaker" minOccurs="0" maxOccurs="unbounded"/> And the XML/RDF: <!-- CIM XML Output For switch783:(295854688) --> <cim:Switch rdf:ID="Switch_295854688"> <cim:IdentifiedObject.mRID>Switch_295854688</cim:IdentifiedObject.mRID> <cim:IdentifiedObject.aliasName>Switch_295854688</cim:IdentifiedObject.aliasName> <cim:ConductingEquipment.phases rdf:resource="http://iec.ch/TC57/2009/CIM-schema-cim14#PhaseCode.ABC" /> <cim:Switch.circuit2>0001406</cim:Switch.circuit2> <cim:Equipment.Line rdf:resource="#Line_0001406" />

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  • Comparing two Objects which implement the same interface for equality / equivalence - Design help

    - by gav
    Hi All, I have an interface and two objects implementing that interface, massively simplied; public interface MyInterface { public int getId(); public int getName(); ... } public class A implements MyInterface { ... } public class B implements MyInterface { ... } We are migrating from using one implementation to the other but I need to check that the objects of type B that are generated are equivalent to those of type A. Specifically I mean that for all of the interface methods an object of Type A and Type B will return the same value (I'm just checking my code for generating this objects is correct). How would you go about this? Map<String, MyInterface> oldGeneratedObjects = getOldGeneratedObjects(); Map<String, MyInterface> newGeneratedObjects = getNewGeneratedObjects(); // TODO: Establish that for each Key the Values in the two maps return equivalent values. I'm looking for good coding practices and style here. I appreciate that I could just iterate through one key set pulling out both objects which should be equivalent and then just call all the methods and compare, I'm just thinking there may be a cleaner, more extensible way and I'm interested to learn what options there might be. Would it be appropriate / possible / advised to override equals or implement Comparable? Thanks in advance, Gavin

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  • Entity Framework POCO objects

    - by Dan
    I'm struggling with understanding Entity Framework and POCO objects. Here's what I'm trying to achieve. 1) Separate the DAL from the Business Layer by having my business layer use an interface to my DAL. Maybe use Unity to create my context. 2) Use Entity Framework inside my DAL. I have a Domain model with objects that reside in my business layer. I also have a database full of tables that doesn't really represent my domain model. I setup Entity Framework and generated POCO objects by using the ADO.NET POCO Generator extension. This gave me an object for each table in my database. Now I want to be able to say context.GetAll<User>(); and have it return a list of my User objects. The User object is in my business layer. Is that possible? Does that make sense or am I totally off and should start over? I'm guessing I need to use the repository pattern to achieve this, but I'm not sure. Can anyone help?

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  • What is the best way to find a processed memory allocations in terms of C# objects

    - by Shantaram
    I have written various C# console based applications, some of them long running some not, which can over time have a large memory foot print. When looking at the windows perofrmance monitor via the task manager, the same question keeps cropping up in my mind; how do I get a break down of the number objects by type that are contributing to this footprint; and which of those are f-reachable and those which aren't and hence can be collected. On numerous occasions I've performed a code inspection to ensure that I am not unnecessarily holding on objects longer than required and disposing of objects with the using construct. I have also recently looked at employing the CG.Collect method when I have released a large number of objects (for example held in a collection which has just been cleared). However, I am not so sure that this made that much difference, so I threw that code away. I am guessing that there are tools in sysinternals suite than can help to resolve these memory type quiestions but I am not sure which and how to use them. The alternative would be to pay for a third party profiling tool such as JetBrains dotTrace; but I need to make sure that I've explored the free options first before going cap in hand to my manager.

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  • Reference to the Main Form whilst trying to Serialize objects in C#

    - by Paul Matthews
    I have a button on my main form which calls a method to serialize some objects to disk. I am trying to add these objects to an ArrayList and then serialize them using a BinaryFormatter and a FileStream. public void SerializeGAToDisk(string GenAlgName) { // Let's make a list that includes all the objects we // need to store a GA instance ArrayList GAContents = new ArrayList(); GAContents.Add(GenAlgInstances[GenAlgName]); // Structure and info for a GA GAContents.Add(RunningGAs[GenAlgName]); // There may be several running GA's using (FileStream fStream = new FileStream(GenAlgName + ".ga", FileMode.Create, FileAccess.Write, FileShare.None)) { BinaryFormatter binFormat = new BinaryFormatter(); binFormat.Serialize(fStream, GAContents); } } When running the above code I get the following exception: System.Runtime.Serialization.SerializationException was unhandled Message=Type 'WindowsFormsApplication1.Form1' in Assembly 'GeneticAlgApp, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' is not marked as serializable. So that means that somewhere in the objects I'm trying to save there must be a reference to the main form. The only possible references I can see are 3 delegates which all point to methods in the main form code. Do delegates get serialized as well? I can't seem to apply the [NonSerialized] attribute to them. Is there anything else I might be missing? Even better, is there a quick method to find the reference(s) that are causing the problem?

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  • how do I best create a set of list classes to match my business objects

    - by ken-forslund
    I'm a bit fuzzy on the best way to solve the problem of needing a list for each of my business objects that implements some overridden functions. Here's the setup: I have a baseObject that sets up database, and has its proper Dispose() method All my other business objects inherit from it, and if necessary, override Dispose() Some of these classes also contain arrays (lists) of other objects. So I create a class that holds a List of these. I'm aware I could just use the generic List, but that doesn't let me add extra features like Dispose() so it will loop through and clean up. So if I had objects called User, Project and Schedule, I would create UserList, ProjectList, ScheduleList. In the past, I have simply had these inherit from List< with the appropriate class named and then written the pile of common functions I wanted it to have, like Dispose(). this meant I would verify by hand, that each of these List classes had the same set of methods. Some of these classes had pretty simple versions of these methods that could have been inherited from a base list class. I could write an interface, to force me to ensure that each of my List classes has the same functions, but interfaces don't let me write common base functions that SOME of the lists might override. I had tried to write a baseObjectList that inherited from List, and then make my other Lists inherit from that, but there are issues with that (which is really why I came here). One of which was trying to use the Find() method with a predicate. I've simplified the problem down to just a discussion of Dispose() method on the list that loops through and disposes its contents, but in reality, I have several other common functions that I want all my lists to have. What's the best practice to solve this organizational matter?

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  • WCF data services - Limiting related objects returned based on critera

    - by Mike Morley
    I have an object graph consisting of a base employee object, and a set of related message objects. I am able to return the employee objects based on search criteria on the employee properties (eg team) etc. However, if I expand on the messages, I get the full collection of messages back. I would like to be able to either take the top n messages (i.e. restrict to 10 most recent) or ideally use a date range on the message objects to limit how many are brought back. So far I have not been able to figure out a way of doing this: I get an error if I attempt to filter on properties on the message (&$filter=employee/message/StartDate gives an error "No property 'StartDate' exists in type 'System.Data.Objects.DataClasses.EntityCollection`1). Attempting to use Top on the message related object doesn't work either. I have also tried using a WebGet extension that takes a string list of employee IDs. That works until the list gets too long, and then fails due to the URL getting too long (it might be possible to setup a paging mechanism on this approach)... Unfortunately the UI control I am using requires the data to be in a fairly specific hierarchical shape, so I can't easily come at this from starting on the message side and working backwards. Outside of making multiple calls does anyone know of a method to accomplish this with wcf data services? Thanks! M.

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  • Inversion of control domain objects construction problem

    - by Andrey
    Hello! As I understand IoC-container is helpful in creation of application-level objects like services and factories. But domain-level objects should be created manually. Spring's manual tells us: "Typically one does not configure fine-grained domain objects in the container, because it is usually the responsibility of DAOs and business logic to create/load domain objects." Well. But what if my domain "fine-grained" object depends on some application-level object. For example I have an UserViewer(User user, UserConstants constants) class. There user is domain object which cannot be injected, but UserViewer also needs UserConstants which is high-level object injected by IoC-container. I want to inject UserConstants from the IoC-container, but I also need a transient runtime parameter User here. What is wrong with the design? Thanks in advance! UPDATE It seems I was not precise enough with my question. What I really need is an example how to do this: create instance of class UserViewer(User user, UserService service), where user is passed as the parameter and service is injected from IoC. If I inject UserViewer viewer then how do I pass user to it? If I create UserViewer viewer manually then how do I pass service to it?

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  • Avoiding duplicate objects in Java deserialization

    - by YGL
    I have two lists (list1 and list2) containing references to some objects, where some of the list entries may point to the same object. Then, for various reasons, I am serializing these lists to two separate files. Finally, when I deserialize the lists, I would like to ensure that I am not re-creating more objects than needed. In other words, it should still be possible for some entry of List1 to point to the same object as some entry in List2. MyObject obj = new MyObject(); List<MyObject> list1 = new ArrayList<MyObject>(); List<MyObject> list2 = new ArrayList<MyObject>(); list1.add(obj); list2.add(obj); // serialize to file1.ser ObjectOutputStream oos = new ObjectOutputStream(...); oos.writeObject(list1); oos.close(); // serialize to file2.ser oos = new ObjectOutputStream(...); oos.writeObject(list2); oos.close(); I think that sections 3.4 and A.2 of the spec say that deserialization strictly results in the creation of new objects, but I'm not sure. If so, some possible solutions might involve: Implementing equals() and hashCode() and checking references manually. Creating a "container class" to hold everything and then serializing the container class. Is there an easy way to ensure that objects are not duplicated upon deserialization? Thanks.

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  • Where to place interactive objects in JavaScript?

    - by Chris
    I'm creating a web based application (i.e. JavaScript with jQuery and lots of SVG) where the user interacts with "objects" on the screen (think of DIVs that can be draged around, resized and connected by arraows - like a vector drawing programm or a graphical programming language). As each "object" contains individual information but is allways belonging to a "class" of elements it's obvious that this application should be programmed by using an OOP approach. But where do I store the "objects" best? Should I create a global structure ("registry") with all (JS native) objects and tell them "draw yourself on the DOM"? Or should I avoid such a structure and think of the (relevant) DOM nodes as my objects and attach the relevant data as .data() to them? The first approach is very MVC - but I guess the attachment of all the event handlers will be non trivial. The second approach will handle the events in a trivial way and it doesn't create a duplicate structure, but I guess the usual OO stuff (like methods) will be more complex. What do you recomend? I think the answer will be JavaScript and SVG specific as "usual" programming languages don't have such a highly organized output "canvas".

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  • UIDs for data objects in MySQL

    - by Callash
    Hi there, I am using C++ and MySQL. I have data objects I want to persist to the database. They need to have a unique ID for identification purposes. The question is, how to get this unique ID? Here is what I came up with: 1) Use the auto_increment feature of MySQL. But how to get the ID then? I am aware that MySQL offers this "SELECT LAST_INSERT_ID()" feature, but that would be a race condition, as two objects could be inserted quite fast after each other. Also, there is nothing else that makes the objects discernable. Two objects could be created pretty much at the same time with exactly the same data. 2) Generate the UID on the C++ side. No dice, either. There are multiple programs that will write to and read from the database, who do not know of each other. 3) Insert with MAX(uid)+1 as the uid value. But then, I basically have the same problem as in 1), because we still have the race condition. Now I am stumped. I am assuming that this problem must be something other people ran into as well, but so far, I did not find any answers. Any ideas?

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  • How to synchronize access to many objects

    - by vividos
    I have a thread pool with some threads (e.g. as many as number of cores) that work on many objects, say thousands of objects. Normally I would give each object a mutex to protect access to its internals, lock it when I'm doing work, then release it. When two threads would try to access the same object, one of the threads has to wait. Now I want to save some resources and be scalable, as there may be thousands of objects, and still only a hand full of threads. I'm thinking about a class design where the thread has some sort of mutex or lock object, and assigns the lock to the object when the object should be accessed. This would save resources, as I only have as much lock objects as I have threads. Now comes the programming part, where I want to transfer this design into code, but don't know quite where to start. I'm programming in C++ and want to use Boost classes where possible, but self written classes that handle these special requirements are ok. How would I implement this? My first idea was to have a boost::mutex object per thread, and each object has a boost::shared_ptr that initially is unset (or NULL). Now when I want to access the object, I lock it by creating a scoped_lock object and assign it to the shared_ptr. When the shared_ptr is already set, I wait on the present lock. This idea sounds like a heap full of race conditions, so I sort of abandoned it. Is there another way to accomplish this design? A completely different way?

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  • Suggestion on algorithm to distribute objects of different value

    - by Unknown
    Hello, I have the following problem: Given N objects of different values (N < 30, and the values are multiple of a "k" constant, i.e. k, 2k, 3k, 4k, 6k, 8k, 12k, 16k, 24k and 32k), I need an algorithm that will distribute all items to M players (M <= 6) in such a way that the total value of the objects each player gets is as even as possible (in other words, I want to distribute all objects to all players in the fairest way possible). I don't need (pseudo)code to solve this (also, this is not a homework :) ), but I'll appreciate any ideas or links to algorithms that could solve this. Thanks!

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  • Problem with fetching dictionary objects in array from plist iphone sdk

    - by neha
    Hi all, What is the datatype you use to fetch items whose type is dictionary in plist i.e. nsmutabledictionary or nsdictionary? Because I'm using following code to retrieve dictionary objects from an array of dictionaries in plist. NSMutableDictionary *_myDict = [contentArray objectAtIndex:0]; NSLog(@"MYDICT : %@",_myDict); NSString *myKey = (NSString *)[_myDict valueForKey:@"Contents"] ; [[cell lblFeed] setText:[NSString stringWithFormat:@"%@",myKey]]; Here, on first line it's showing me objc_msgsend. ContentArray is an nsarray and it's contents are showing 2 objects that are there in plist. In plist they are dictionary objects. Then why this error? Can anybody please help? Thanx in advance.

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