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• How to change order in ordered+persisted collection?

  - by Jaroslav Záruba

  I just need to change order of items in a (previously persisted) ordered collection... I tried simply passing the re-arranged collection to a setter: after committing a transaction the collection is gone. Then I tried to clear() the existing collection and addAll() afterwards: clear() makes persistent manager to mark all the elements as deleted. (But obviously I would like to be able to work with the collection items in the very transaction.) (The collection is not in a default fetch group, so I tried the above also with the named fetch group added into the fetch plan. No luck.) This must be the most stupid question, but I ran out of ideas and I'm stuck here two days already. I swear I googled. :(

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• NSFetchedResultsController doesn't fetch up the child-parent moc chain?

  - by Kronusdark

  I cannot find any clarification on this, so it may be a bug. Problem is, I have a series of parent-child Managed Object Context's. When I save on a child context the changes get pushed up to the parent, and I can fetch using a plain old NSFetchRequest. However, if I rely on an NSFetchedResultsController to pull these changes into a sibling context to the first, they do not see them. calling -(void)performFetch: error; doesn't seem to pull the changes either. After a restart of the app, all new data is available. My hypothesis is that NSFetchedResultsController only fetches from its current context and will not follow the chain to the persistent store. Can someone please set me straight here? Am I going to have to use notifications to monitor changes on other contexts? and finally, is this mentioned somewhere in the doc's? I cannot find it for the life of me.

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• CORE DATA objectId changes constantly

  - by mongeta

  Hello, I have some data that I export into an XML file and put in a remote FTP Server. I have to identified each object with a unique attribute, it doesn't matter wich is, but must be persistent always = it can never change. I don't want to create a unique attribute, sequence, serial, etc. I'm using the objectID but every time I use it a get a new reference. I know that before the object has been saved, it has a 'temporal id', but once it's saved, it gets the definitive. I'm not seeing this, never. When I export, just fetch all data and loop, and always I get a new reference: NSURL *objectID = [[personalDataObject objectID] URIRepresentation]; // some of id received for the SAME OBJECT (no changes made, saved, ...) // 61993296 // 62194624 thanks, r. edit I was using %d instead of %@, now the returned data is: x-coredata://F46F3300-8FED-4876-B0BF-E4D2A9D80913/DataEntered/p1 x-coredata://F46F3300-8FED-4876-B0BF-E4D2A9D80913/DataEntered/p2

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• MySQL dual license behavior

  - by jromero

  Hi SO, I'm running a commercial(closed source) Web App development for the first time. Initially I considered MySQL the most feasible option for a DB, until I get quite confused about its dual license behavior. If I want a commercial application do I still can use the GPL version of MySQL or I must get a license? The same question in a different way: If I use MySQL's GPL version does that force me to license the whole app under GPL? Either case I would go with PostgreSQL, I just want to make really really sure about this. Even in SO I've seen related("duplicates") questions but never a clear answer... All other tools I'm gonna use to code the project are licensed under BSD or MIT. Just in case, the role of MySQL in the project is merely as relational DB to store persistent data and query it. I'd really appreciate if someone can clarify this for me. Regards, thanks in advanced.

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• .NET ORM and Security

  - by Sphynx

  We're going to use an ORM tool with a .NET desktop application. The tool allows creation of persistent classes. It generates all database tables automatically. In addition to other data, our system needs to store user credentials, and deliver access control. The question is, is there any possibility of access control by means of ORM, without creating the database authentication mechanisms manually? Is there any product on the market which allows this? We thought of limiting the access in the program itself, but users can easily access the database directly, and bypass the program limitations. Thanks.

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• What interprocess locking calls should I monitor?

  - by Matt Joiner

  I'm monitoring a process with strace/ltrace in the hope to find and intercept a call that checks, and potentially activates some kind of globally shared lock. While I've dealt with and read about several forms of interprocess locking on Linux before, I'm drawing a blank on what to calls to look for. Currently my only suspect is futex() which comes up very early on in the process' execution. Update0 There is some confusion about what I'm after. I'm monitoring an existing process for calls to persistent interprocess memory or equivalent. I'd like to know what system and library calls to look for. I have no intention call these myself, so naturally futex() will come up, I'm sure many libraries will implement their locking calls in terms of this, etc. Update1 I'd like a list of function names or a link to documentation, that I should monitor at the ltrace and strace levels (and specifying which). Any other good advice about how to track and locate the global lock in mind would be great.

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• declaring a 2D array of pointer objects

  - by Tyler Stennette

  I'm having a tough time figuring out how to instantiate a 2D array of pointer objects. Here is how I'm doing it: Pieces* chessBoard[9][9]; When I want to set it to an actual object pointer, I'm doing the following: chessBoard[1][1] = new Rook(p1Rook); Rook is a class that inherits attributes from the Pieces class and p1Rook is a char variable set to 'R'. This class also implements virtual functions (not pure virtual) from Pieces such as move() or getPiece() that are unique to the particular chess piece. However, when I compile my program, I get the following error: ChessBoard.cpp:69: error: expected type-specifier before ‘Rook’ ChessBoard.cpp:69: error: cannot convert ‘int*’ to ‘Pieces*’ in assignment Can someone please explain what I should change to get rid of this rather annoying persistent error? I would appreciate it.

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• What is the most efficient way to store a mapping "key -> event stream"?

  - by jkff

  Suppose there are ~10,000's of keys, where each key corresponds to a stream of events. I'd like to support the following operations: push(key, timestamp, event) - pushes event to the event queue for key, marked with the given timestamp. It is guaranteed that event timestamps for a particular key are pushed in sorted or almost sorted order. tail(key, timestamp) - get all events for key since the given timestamp. Usually the timestamp requests for a given key are almost monotonically increasing, almost synchronously with pushes for the same key. This stuff has to be persistent (although it is not absolutely necessary to persist pushes immediately and to keep tails with pushes strictly in sync), so I'm going to use some kind of database. What is the optimal kind of database structure for this task? Would it be better to use a relational database, a key-value storage, or something else?

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• amazon design doubt

  - by praveen

  I was looking at the amazon website and was wondering how one of the feature would have been implemented. The feature : what customers buy after viewing a particular item. If i were to develop such a feature i would probably generate a session id for each user session and store the session id-page id combination in a log file. and if a book is bought set a separate flag for the session id-page id. A separate program can then be run on the log file periodically, to identify the groups that were bought together/viewed together and that information can be stored in a persistent file. This is ofcourse a simple solution without taking into consideration the distributed nature of the servers - but would this suffice or can you help me identify a better design.

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• Replacing Resource files on new BlackBerry app version

  - by Jeff

  Hello, I am maintaining an existing BlackBerry application (implemented as a MIDlet). The application contains a number of data files that get bundled with the app as resources. Some of these data files need to be updated for a new version of the app. When the user goes to install a new version of the application (via URL of Jad file), it prompts them with the following message "Persistent data exists for the application. Would you like to retain this data? " If the user selects "Yes", it looks like the app continues to use the old resource files. This is so surprising to me. First of all, am I losing my mind or will an upgrade really not overwrite existing resource files? Is there any way I can force it to? Thanks, Jeff

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• Migrating a Core Data Store from iCloud to local

  - by schmok

  I'm currently struggling with Core Data iCloud migration. I want to move a store from an iCloud ubiquity container (.nosync) to a local URL. Problem is whenever I call something like this: NSPersistentStore *newStore = [self.persistentStoreCoordinator migratePersistentStore: currentiCloudStore toURL: localURL options: nil withType: NSSQLiteStoreType error: &error]; I get this error: -[NSPersistentStoreCoordinator addPersistentStoreWithType:configuration:URL:options:error:](1055): CoreData: Ubiquity: Error: A persistent store which has been previously added to a coordinator using the iCloud integration options must always be added to the coordinator with the options present in the options dictionary. If you wish to use the store without iCloud, migrate the data from the iCloud store file to a new store file in local storage. file://localhost/Users/sch/Library/Containers/bla/Data/Documents/tmp.sqlite. This will be a fatal error in a future release Anyone ever seen this error? Maybe I'm just missing the right migration options?

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• JDO in Google App Engine: order of keys in unowned one-to-many relationship

  - by Kel

  I'm implementing web application with JDO in Google App Engine. According to documentation, in owned one-to-many relationships, order of elements in "owner" object collection is determined either by automatically created index field, or by information given in explicit ordering clause. For example: @PersistenceCapable public class Person { // ... @Order(extensions = @Extension(vendorName="datanucleus", key="list-ordering", value="country asc, city asc")) private List<ContactInfo> contacts = new List<ContactInfo>(); In unowned relationships, "owner" object contains collection of keys of "nested" objects, for example: @PersistenceCapable public class Author { // ... @Persistent private List<Key> books; Is order of keys preserved, if I use List<Key> collection in "owner" object for storing keys of "nested" elements? I could not find answer neither in JDO relationships article, nor in Data Classes article :(

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• Connect to Oracle database on a different server from PHP

  - by macha

  Hello I have a database engine sitting on a remote server, while my webserver is present locally. I have worked pretty much with client-server architecture, where the server has both the webserver and the database engine. Now I need to connect to an Oracle database which is situated on a different server. Can anybody give me any suggestions?? I believe ODBC_CONNECT might not work. Do I use OCI8 drivers?? How would I connect to my database server. Also I would have a very high number of database calls going back and forth, so is it good to go with persistent connection or do I still use individual database calls?

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• Blackberry Code

  - by Haoest

  I have having difficulties protecting my blackberry application persistent data with ControlledAccess object. According to http://www.blackberry.com/developers/docs/4.5.0api/net/rim/device/api/system/PersistentObject.html, I need a PersistentObject, CodeSignKey, and ControlledAccess objects to work. I have everything except one piece: CodeSignKey codeSigningKey = CodeSigningKey.get( "ACME" ); here, I don't know what to replace for "ACME". Is this the PIN code I chose as I filled out the Code Sign Key? Is it my package name, output file name? The Blackberry API documentation doesn't seem to say anything about this particularly important parameter. Help please, thanks.

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• How to handle updating JDO class definitions on Google App Engine

  - by Spines

  I'm using the Google app engine and JDO. What is the best way to update a JDO class definition without having to wipe the data store contents first? I'm not sure if this is specific to JDO on GAE, but I noticed that when I simply change the name of one of my persistent fields from svotes to votes, an exception is thrown (java.lang.NoSuchFieldError: svotes). I expect once my site goes live I might want to make some changes to my JDO class definitions, such as adding a field or something. Any suggestions for how to update the data definitions without having to wipe the database?

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• How does one declare the type of an Android preference?

  - by David R.

  I have a preferences.xml that looks like this: <?xml version="1.0" encoding="utf-8"?> <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"> <EditTextPreference android:name="Sample" android:enabled="true" android:persistent="true" android:summary="Sample" android:defaultValue="3.0" android:title="Sample" android:key="sample" /> </PreferenceScreen> When I do sp.getString("sample", "3.0"), it works fine and returns a string, but it shouldn't be a string, it should be a float. Running sp.getFloat("sample", 3.0f) throws a ClassCastException because it is a string. What should I put in the XML so that the preference is stored as a float?

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• Keeping connection to APNs open on App Engine using Modules in Go

  - by user3727820

  I'm trying to implement iOS push notifications for a messageboard app I've written (so like notification for new message ect. ect.) but have no real idea where to start. Alot the current documentation seems to be out of date in regard to keeping persistent TLS connections open to the APNs from App Engine and links to articles about depreciated backends I'm using the Go runtime and just keep getting stuck. For instance, the creation of the socket connection to APNs requires a Context which can only be got from a HTTP request, but architecturally this doesn't seem to make a lot of sense because ideally the socket remains open regardless. Is there any clearer guides around that I'm missing or right now is it a better idea to setup a separate VPS or compute instance to handle it?

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• Is it OK to mixed NumberLong and normal integers in the same field in MongoDB?

  - by Nicholas Tolley Cottrell

  I have been using Morphia to persistent objects from Java. I have also been running some batch processes from the console. I just realised that some values are now stored as NumberLong and number as plain Javascript numbers. I have an index on this field. Everything seems to be ok, but if I query: {f: 100} from the console it still returns the object even if it actually contains {f: NumberLong(100)} Is this true of all the drivers? It is best practice to avoid NumberLong is I can fit the value inside 32-bit? Will I save a lot of data and index space if I convert all NumberLongs to basic numbers?

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• Streaming multiple TObjects to a TMemoryStream

  - by Altar

  I need to store multiple objects (most of them are TObject/non persistent) to a TMemoryStream, save the stream to disk and load it back. The objects need to be streamed one after each other. Some kind of universal container. I started to make several functions that store stuff to stream - for example function StreamReadString(CONST MemStream: TMemoryStream): string; StreamWriteString(CONST MemStream: TMemoryStream; s: string); However, it seems that I need to rewrite a lot of code. One of the many examples is TStringList.LoadFromStream that will not work so it needs to be rewritten. This is because TStringList needs to be the last object in the stream (it reads from current position to the end of the stream). Anybody knows a library that provide basic functionality like this? I am using Delphi 7 so RTTI won't help too much.

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• Php getting too many connections error from MySQL

  - by uzioriluzan

  Hello everyone, I am using MySQL and PHP with 2 application servers and 1 database server. With the increase of the number of users (around 1000 by now), I'm getting the following error : SQLSTATE[08004] [1040] Too many connections The parameter "max_connections" is set to "1000" in my.cnf and "mysql.max_persistent" is set to -1 in php.ini. There are at most 1500 apache processes running at a time since the "MaxClients" apache parameter is equal to 750 and we have 2 application servers. Should I raise the "max_connections" to 1500 as indicated in here? Or should I set "mysql.max_persistent" to 750 (we use PDO with persistent connections for performance reasons since the database server is not the same as the application servers)? Or should I try something else? Thanks in advance!

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• What's a good way to throw and handle events in PHP?

  - by techexpert

  Hi everyone, I am just trying to get a general idea about the event prcessing mechanism in PHP5 in as neat way as possible. First of all I understand that a PHP application is not exactly a persistent type, so the events may not make a lot of sense, but from the OO perspective it might be a very elegant way to "communicate" between the objects. So I am thinking that it would make sense to separate the events on the external events, such as $_POST & $_GET and the internal ones, i.e. function callbacks. As far as the external ones, is it a good idea to process the $_GETs and $_POSTs directly, or is it better to wrap them into an event of some sort? Also, in order to process the internal events, do you have to pass the reference to the event handler/dispatcher to each class so they know how to throw them? I was thinking to use the PEAR EventDispatcher to do the work, but I am open to other suggestions. Thank you!

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• Fault exception trashes a register causing a crash in [NSInvocation invoke]

  - by Mike Weller

  I have an NSOperation which fetches some objects from a core data persistent store and sums up a few totals. Sometimes an object is deleted while the operation in in progress, so a core data fault exception occurs. I try/catch the exception while summing to ignore it because I just want to skip objects that cannot be faulted in. However, when one of these fault exceptions occurs (and I swallow it) there is a crash after the invocation returns in [NSInvocation invoke]. It's a bad memory access when dereferencing the value in r10 which according to GDB on a successful run points to one of these: (gdb) x 0x38388348 0x38388348 <OBJC_IVAR_$_NSInvocation._retdata>: 0x00000008 If a fault exception occured a value of 0x02 is in the register which causes the crash. A quick google search tells me that r10 should be saved by the callee, meaning it is not being restored by whatever code is changing it when this exception occurs. Can anybody explain this? I'm not an expert when it comes to these kinds of low-level details

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• function to efficiently check a change of value in a nested hashmap

  - by zcaudate

  the motivation is for checking what has changed in a deeply nest map, kind of like a reverse of update-in. This is a simple example: (def p1 {:a {:a1 :1 :a2 :2} :b {:b1 :1 :b2 :2}}) (def p2 (update-in p1 [:a :a1] (constantly :updated)) ;; => {:a {:a1 :updated :a2 :2} ;; :b {:b1 :1 :b2 :2}} (what-changed? p1 p2) ;; => {:keys [:a :a1] :value :updated) (what-changed? p2 p1) ;; => {:keys [:a :a1] :value :2) I'm hoping that because clojure maps are persistent data-structures, there may be a smart algorithm to figure this out by looking at the underlying structure as opposed to walking through the nested maps and comparing the difference.

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• Does anyone else think instance variables are problematic in database-backed applications?

  - by Ben Aston

  It occurs to me that state control in languages like C# is not well supported. By this, I mean, it is left upto the programmer to manage the state of in-memory objects. A common use-case is that instance variables in the domain-model are copies of information residing in persistent storage (i.e. the database). Clearly this violates the single point of authority principle, and "synchronisation" has to be managed by the developer. I envisage a system where instead of instance variables, we have simple public access/mutator methods marked with attributes that link them to the database, and where reads and writes are mediated by a framework that decides whether to hit the database. Does such a system exist? Am I completely missing the point, or is there some truth to this idea?

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• message queue : selection and sizing

  - by user238591

  Hi, I have 20 messages/s, each 1 - 1.5 Mbytes. I need High Availability (2 to 4 servers min). I need low latencey (high daily volume - full RAM prefered). I need persistent poisoned messages queue. Only few clients (about 16), locally. I can have 12-16G bytes RAM per server (brooker). Which JMS message queue / messaging would you recommend ? On what configuration (CPU/RAM) ? Can I propose optionnal NAS persistence (in case of final delivery failure) ? Thanks

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