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• How do I do automatic data serialization of data objects in Haskell

  - by Adam Gent

  One of the huge benefits in languages that have some sort of reflection/introspecition is that objects can be automatically constructed from a variety of sources. For example in Java I can use the same objects for persisting to a db (with Hibernate) serializing to XML (with JAXB) or serializing to JSON (json-lib). You can do the same in Ruby and Python also usually following some simple rules for properties or annotations for Java. Thus I don't need lots "Domain Transfer Objects". I can concentrate on the domain I am working in. It seems in very strict FP like Haskell and Ocaml this is not possible. Particularly Haskell. The only thing I have seen is doing some sort of preprocessing or meta-programming (ocaml). Is it just accepted that you have to do all the transformations from the bottom upwards? In other words you have to do lot of boring work to turn a data type in haskell into JSON/XML/DB Row object and back again into a data object.

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• Core Data => Adding a related object always nil

  - by mongeta

  Hello, I have two tables related: DataEntered and Model DataEntered -currentModel Model One DataEntered can have only ONE Model, but a Model can stay into many DataEntered. The relationship is from DataEntered to Model (No To Many-relathionship) and no inverse relation. XCode generates the setters for DataEnteredModel: @property (nonatomic, retain) NSSet * current_model; - (void)addCurrent_modelObject:(CarModel *)value; - (void)addCurrent_model:(NSSet *)value; I have a Table and when I select a model, I want to store it to DataEntered: Model *model = [fetchedResultsController objectAtIndexPath:indexPath]; NSLog(@"Model %@",model.name); // ==> gives me the correct model name [dataEntered addCurrent_modelObject:model]; // ==> always nil [dataEntered setCurrent_model:[fetchedResultsController objectAtIndexPath:indexPath]]; // the same, always nil what I'm doing wrong ????? thanks, r.

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• Efficient data structure for fast random access, search, insertion and deletion

  - by Leonel

  I'm looking for a data structure (or structures) that would allow me keep me an ordered list of integers, no duplicates, with indexes and values in the same range. I need four main operations to be efficient, in rough order of importance: taking the value from a given index finding the index of a given value inserting a value at a given index deleting a value at a given index Using an array I have 1 at O(1), but 2 is O(N) and insertion and deletions are expensive (O(N) as well, I believe). A Linked List has O(1) insertion and deletion (once you have the node), but 1 and 2 are O(N) thus negating the gains. I tried keeping two arrays a[index]=value and b[value]=index, which turn 1 and 2 into O(1) but turn 3 and 4 into even more costly operations. Is there a data structure better suited for this?

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• Best data-structure to use for two ended sorted list

  - by fmark

  I need a collection data-structure that can do the following: Be sorted Allow me to quickly pop values off the front and back of the list Remain sorted after I insert a new value Allow a user-specified comparison function, as I will be storing tuples and want to sort on a particular value Thread-safety is not required Optionally allow efficient haskey() lookups (I'm happy to maintain a separate hash-table for this though) My thoughts at this stage are that I need a priority queue and a hash table, although I don't know if I can quickly pop values off both ends of a priority queue. I'm interested in performance for a moderate number of items (I would estimate less than 200,000). Another possibility is simply maintaining an OrderedDictionary and doing an insertion sort it every-time I add more data to it. Furthermore, are there any particular implementations in Python. I would really like to avoid writing this code myself.

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• What is the best possible technology for pulling huge data from 4 remote servers

  - by Habib Ullah Bahar

  Hello, For one of our project, we need to pull huge real time stock data from 4 remote servers across two countries. The trivial process here, check the sources for a regular interval and save the update to database. But as these are real time stock data of more than 1000 companies, I have to pull every second, which isn't good in case of memory, bandwidth I think. Please give me suggestion on which technology/platform [We are flexible here. PHP, Python, Java, PERL - anyone of them will be OK for us] we should choose, it can be achieved easily and with better performance.

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• Reverting CoreData data

  - by ndg

  I have an NSTableView which is populated via a CoreData-backed NSArrayController. Users are able to edit any field they choose within the NSTableView. When they select the rows that they have modified and press a button, the data is sent to a third-party webservice. Provided the webservice accepts the updated values, I want to commit those values to my persistent store. If, however, the webservice returns an error (or simply fails to return), I want the edited fields to revert to their original values. To complicate matters, I have a number of other editable controls, backed by CoreData, which do not need to resort to this behaviour. I believe the solution to this problem revolves around the creation of a secondary Managed Object context, which I would use only for values edited within that particularly NSTableView. But I'm confused as to how the two MOC would interact with each other. What's the best solution to this problem?

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• What Data structure for Reputation Rules in C# (like stackoverflow)

  - by optician

  I am currently building a system which will have entities that will have scores like reputation etc.. I will have a service that will check for certain rules having been triggered, and will perform certain logic if they are triggered. Previously I have used say an Enum for doing this when I have only had to store an id and a description. public enum ShoppingCratCalculation { PartialCalculation = 1, CompleteCalculation =2 } But in this situation I want to carry more information, such as the modification to reputation, all in one place. I'm essentially asking what data structure would be best suited to storing this information, for each rule in the system. 1. Description = string ("User forgot to write a review") 2. DB id = int (23) 3. Rep score modification = int (-5) Maybe a little class (Rule) with these as properties , and then just a list? Does anyone have any best practice suggestions for this kind of struct?

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• How can I compare Core Data models?

  - by Don

  I noticed while doing system testing that a feature of our app had been removed. It looks like at some point, an older version of a file was checked into SVN that was missing a property. This specific file was generated from the Core Data model, and sure enough, the latest version of the model in SVN is missing the same attribute. I need to find out if any other attributes are missing, or if anything else in the model changed. However, the elements file in the .xcodedatamodel folder appears to binary and I can't compare the revisions. Is there a way to find the differences between two Core Data models in SVN? Barring that, what would be the best way to accomplish this task?

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• Core Data and Relationships

  - by alku83

  I have two objects, a Trip and a Place. A Trip represents a journey from one Place to another Place, ie. a Trip needs a fromPlace and a toPlace. So, this is a 1-to-2 relationship, but I need to know which is the "from" and which is the "to". I am not sure how to model this in Core Data. I have created two entities (Trip, Place), and now I want to setup the relationship(s) so I have a fromPlace and a toPlace. Do I need to add an extra field on the Place entity called isFrom, or similar? If this was in a database, I would just have a id column on the Place table, and then two columns in the Trip table - fromPlaceId and toPlaceId. How do I achieve something similar in Core Data?

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• Storing a bucket of numbers in an efficient data structure

  - by BlitzKrieg

  I have a buckets of numbers e.g. - 1 to 4, 5 to 15, 16 to 21, 22 to 34,.... I have roughly 600,000 such buckets. The range of numbers that fall in each of the bucket varies. I need to store these buckets in a suitable data structure so that the lookups for a number is as fast as possible. So my question is what is the suitable data structure and a sorting mechanism for this type of problem. Thanks in advance

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• Queue-like data structure with fast search and insertion

  - by Max

  I need a datastructure with the following properties: It contains integer numbers, no duplicates. After it reaches the maximal size the first element is removed. So if the capacity is 3, then this is how it would look when putting in it sequential numbers: {}, {1}, {1, 2}, {1, 2, 3}, {2, 3, 4}, {3, 4, 5} etc. Only two operations are needed: inserting a number into this container (INSERT) and checking if the number is already in the container (EXISTS). The number of EXISTS operations is expected to be approximately 2 * number of INSERT operations. I need these operations to be as fast as possible. What would be the fastest data structure or combination of data structures for this scenario?

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• Data Structure for a particular problem??

  - by AGeek

  Hi, Which data structure can perform insertion, deletion and searching operation in O(1) time in the worst case. We may assume the set of elements are integers drawn from a finite set 1,2,...,n, and initialization can take O(n) time. I can only think of implementing a hash table. Implementing it with Trees will not give O(1) time complexity for any of the operation. Or is it possible?? Kindly share your views on this, or any other data structure apart from these.. Thanks..

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• Transferring Data Between Server and Client (Mobile)

  - by Byron

  Scenario: Client (Mobile) - .Net CF 2.0, SQL CE 3.0 Server - .Net 2.0, SQL Server 2005, Web Service Client and Server database schemas differ. From server - only certain columns from certain tables need to be synced. From client - everything will need to be synced once client has made changes. Client will continually poll a web service to download and upload data. A framework will be developed to package and unpackage data, used by both client and server. How would you develop the packaging and unpackaging? Use datasets, serialise strongly typed objects? All suggestions welcome. Thanks

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• What are the restrictions for the name of an application when submitting to App Store ?

  - by Patrick

  Hello, I have just finished my application for iPhone. I would like to know if it is possible to use the word iPhone in the name of the application. For example, can I name my application iPhonesque ? And for the icon, can I use graphics related to Apple like a Mac Windows (with the three buttons, red, yellow and green) on snow leopard background ? Thank you very much for your answers.

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• Which data structure for List of objects + datagrid wiev

  - by Martin

  Hi, I have to develop a code which will store a list of objects, as example below 101, value 11, value 12, value 13 ...etc 102, value 21, value 22, value 23 ...etc 103, value 31, value 32, value 33 ...etc 104, value 41, value 42, value 43 ...etc Now, the difficulty is, that first column is an identifier, and whole table should always be sorted by it. Easy access to each element is required. Additionally, list should be easily updated, and extended by adding element at the end as well as in front and still keep being sorted by first column. Finally, I would like to be able to display values of the above in datagridview. What is most important is a performance of the implementation, as rows will be updated many times per second, and datagridview should be able to display all changes immediately. I was thinking about creating class for the values, and then a Dictionary but encountered a problem with displaying values in gridview. What would be the most optimal way of implementing the code? Thanks in advance Martin

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• Adding single row one by one in tableview from core data of iPhone

  - by user336685

  I am working on RSS reader code where articles get downloaded and are viewable offline. The problem is only after all articles are downlaoded the tableview containing headlines gets updated. Core data is used. So everytime NSobjectcontext is saved , [self tableview updatebegins ] is called.The table is getting updated via fetchcontroller core data. I tried saving NSobjectcontext everytime an article is saved but that is not updating the tableview. I want a mechanism similar to instapaper tableview where articles get saved and tableview gets updated immediately. Please help if you know the solution. Thanks in advance.

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• Core Data and BOOL setup

  - by John Valen

  I am working on an app that uses Core Data as its backend for managing SQLite records. I have everything working with strings and numbers, but have just tried adding BOOL fields and can't seem to get things to work. In the .xcdatamodel, I have added a field to my object called isCurrentlyForSale which is not Optional, not Transient, and not Indexed. The attribute's type is set to Boolean with default value NO. When I created the class files from the data model, the boilerplate code added for this property in the .h header was: @property (nonatomic, retain) NSNumber * isCurrentlyForSale; along with the @dynamic isCurrentlyForSale; in the .m implementation file. I've always worked with booleans as simple BOOLs. I've read that I could use NSNumber's numberWithBool and boolValue methods, but this seems like an aweful lot of extra code for something so simple. Can the @property in the header be changed to a simple BOOL? If so is there anything to watch out for? Thanks -John

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• AutoComplete implementation - Interview Question

  - by user181218

  Hi, Say you have a DB table with two cols: SearchPhrase(String) | Popularity(Int). You need to initialize a DS so that you could use it to implement an autocomplete feature (like google suggest) comfortably. The requirement: Once the data from the db is processed into the data structure, when you type a letter you get the 10 most popular searchphrases from the db starting with that letter,then when you type the next one you get the 10 .... with these two letters and so on. The question only concerns planning the ds and pseudocoding Insert,Search etc. Note: YOU CANNOT USE TRIE DS. Any ideas?

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• iOS 5 - Coredata Sqlite DB losing data after killing app

  - by Brian Boyle

  I'm using coredata with a sqlite DB to persist data in my app. However, each time I kill my app I lose any data that was saved in the DB. I'm pretty sure its because the .sqlite file for my DB is just being replaced by a fresh one each time my app starts, but I can't seem to find any code that will just use the existing one thats there. It would be great if anyone could point me towards some code that could handle this for me. Cheers B - (NSPersistentStoreCoordinator *)persistentStoreCoordinator { if (__persistentStoreCoordinator != nil) { return __persistentStoreCoordinator; } NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil]; NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"FlickrCoreData.sqlite"]; NSError *error = nil; __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]]; if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:options error:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } return __persistentStoreCoordinator; }

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• ADO.NET Data Service -- non .NET consumers

  - by SwampyFox

  Has anyone come across an example of a non .Net consumer of an ADO.NET Data Service? I am on the second day of looking at what Astoria is and how it can be used. I am also trying to answer why would I use this instead of a web service? After getting my examples running, I kind get the RESTful approach to getting data out the system. And, plugging it into a .net client is incredibly easy. But, then I wondered how a non-.NET consumer would go about it. Any ideas (pointers) definitely appreciated...

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• Data Warehouse: One Database or many?

  - by drrollins

  At my new company, they keep all data associated with the data warehouse, including import, staging, audit, dimension and fact tables, together in the same physical database. I've been a database developer for a number of years now and this consolidation of function and form seems counter to everything I know. It seems to make security, backup/restore and performance management issues more manually intensive. Is this something that is done in the industry? Are there substantial reasons for doing or not doing it? The platform is Netezza. The size is in terabytes, hundreds of millions of rows. What I'm looking to get from answers to this question is a solid understanding of how right or wrong this path is. From your experience, what are the issues I should be focused on arguing if this is a path that will cause trouble for us down the road. If it is no big deal, then I'd like to know that as well.

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• iPhone - Create non-persistent entities in core data

  - by ncohen

  Hi everyone, I would like to use entity objects but not store them... I read that I could create them like this: myElement = (Element *)[NSEntityDescription insertNewObjectForEntityForName:@"Element" inManagedObjectContext:managedObjectContext]; And right after that remove them: [managedObjectContext deleteObject:myElement]; then I can use my elements: myElement.property1 = @"Hello"; This works pretty well even though I think this is probably not the most optimal way to do it... Then I try to use it in my UITableView... the problem is that the object get released after the initialization. My table becomes empty when I move it! Thanks edit: I've also tried to copy the element ([myElement copy]) but I get an error...

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• iPhone app launch times and Core Data migration

  - by sehugg

  I have a Core Data application which I plan to update with a new schema. The lightweight migration seems to work, but it takes time proportional to the amount of data in the database. This occurs in the didFinishLaunchingWithOptions phase of the app. I want to avoid <app> failed to launch in time problems, so I assume I cannot keep the migration in the didFinishLaunchingWithOptions method. I assume the best method would involve performing the migration in a background thread. I assume also that I'd need to defer loading of the main ViewController until the loading completes to avoid using the managedObjectContext until initialization completes. Does this make sense, and is there example code (maybe in Apple sample projects) of this sort of initialization?

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• Better data-structure design

  - by Tempname

  Currently in my application I have a single table that is giving me a bit of trouble. The issue at hand is I have a value object that is mapped to this table. When the data is returned to me as an array of value objects, I have to then loop through this array and begin my recursion by matching the ParentID to parent ObjectID's. The column ParentID is either null (acts a parent) or it holds the value of an ObjectID. I know there has to be a better way to create this data structure so that I do not have to do recursive loops to match ParentID's with their ObjectID's. Any help with this is greatly appreciated. Here is the table in describe form: +----------------+------------------+------+-----+---------------------+-----------------------------+ | Field | Type | Null | Key | Default | Extra | +----------------+------------------+------+-----+---------------------+-----------------------------+ | ObjectID | int(11) unsigned | NO | PRI | NULL | auto_increment | | ObjectHeight | decimal(6,2) | NO | | NULL | | | ObjectWidth | decimal(6,2) | NO | | NULL | | | ObjectX | decimal(6,2) | NO | | NULL | | | ObjectY | decimal(6,2) | NO | | NULL | | | ObjectLabel | varchar(255) | NO | | NULL | | | TemplateID | int(11) unsigned | NO | MUL | NULL | | | ObjectTypeID | int(11) unsigned | NO | MUL | NULL | | | ParentID | int(11) unsigned | YES | MUL | NULL | | | CreationDate | datetime | YES | | 0000-00-00 00:00:00 | | | LastModifyDate | timestamp | YES | | NULL | on update CURRENT_TIMESTAMP | +----------------+------------------+------+-----+---------------------+-----------------------------+e

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• Core Data produces Analyzer warnings

  - by RickiG

  Hi I am doing the final touch ups on an app and I am getting rid of every compiler/analyzer warning. I have a bunch of Class methods that wrap my apps access to Core Data entities. This is "provoking" the analyzer. + (CDProductEntity*) newProductEntity { return (CDProductEntity*)[NSEntityDescription insertNewObjectForEntityForName:@"CDProductEntity" inManagedObjectContext:[self context]]; } Which results in an Analyzer warning: Object with +0 retain counts returned to caller where a +1 (owning) retain count is expected In the method that calls the above Class Method I have this: CDProductEntity *newEntity = [self newProductEntity]; Which results in an Analyzer warning: Method returns an Objective-C object with a +1 retain count (owning reference) Explicitly releasing or autoreleasing a Core Data entity is usually very very bad, but is that what it is asking me to do here? First it tells me it has a +0 retain count and that is bad, then it tells me it has a +1 which is also bad. What can I do to ensure that I am either dealing with a Analyzer hiccup or that I release correctly? Thanks in advance

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