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  • Setting up a "to-many" relationship value dependency for a transient Core Data attribute

    - by Greg Combs
    I've got a relatively complicated Core Data relationship structure and I'm trying to figure out how to set up value dependencies (or observations) across various to-many relationships. Let me start out with some basic info. I've got a classroom with students, assignments, and grades (students X assignments). For simplicity's sake, we don't really have to focus much on the assignments yet. StudentObj <--->> ScoreObj <<---> AssignmentObj Each ScoreObj has a to-one relation with the StudentObj and the AssignmentObj. ScoreObj has real attributes for the numerical grade, the turnInDate, and notes. AssignmentObj.scores is the set of Score objects for that assignment (N = all students). AssignmentObj has real attributes for name, dueDate, curveFunction, gradeWeight, and maxPoints. StudentObj.scores is the set of Score objects for that student (N = all assignments). StudentObj also has real attributes like name, studentID, email, etc. StudentObj has a transient (calculated, not stored) attribute called gradeTotal. This last item, gradeTotal, is the real pickle. it calculates the student's overall semester grade using the scores (ScoreObj) from all their assignments, their associated assignment gradeWeights, curves, and maxPoints, and various other things. This gradeTotal value is displayed in a table column, along with all the students and their individual assignment grades. Determining the value of gradeTotal is a relatively expensive operation, particularly with a large class, therefore I want to run it only when necessary. For simplicity's sake, I'm not storing that gradeTotal value in the core data model. I don't mind caching it somewhere, but I'm having a bitch of a time determining where and how to best update that cache. I need to run that calculation for each student whenever any value changes that affects their gradeTotal. If this were a simple to-one relationship, I know I could use something like keyPathsForValuesAffectingGradeTotal ... but it's more like a many-to-one-to-many relationship. Does anyone know of an elegant (and KVC correct) solution? I guess I could tear through all those score and assignment objects and tell them to register their students as observers. But this seems like a blunt force approach.

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  • CoreData, transient atribute and EXC_BAD_ACCESS.

    - by Lukasz
    I'm trying to build simple file browser and i'm stuck. I defined classes, build window, add controllers, views.. Everything works but only ONE time. Selecting again Folder in NSTableView or trying to get data from Folder.files causing silent EXC_BAD_ACCESS (code=13, address0x0) from main. Info about files i keep outside of CoreData, in simple class, I don't want to save them: #import <Foundation/Foundation.h> @interface TPDrawersFileInfo : NSObject @property (nonatomic, retain) NSString * filename; @property (nonatomic, retain) NSString * extension; @property (nonatomic, retain) NSDate * creation; @property (nonatomic, retain) NSDate * modified; @property (nonatomic, retain) NSNumber * isFile; @property (nonatomic, retain) NSNumber * size; @property (nonatomic, retain) NSNumber * label; +(TPDrawersFileInfo *) initWithURL: (NSURL *) url; @end @implementation TPDrawersFileInfo +(TPDrawersFileInfo *) initWithURL: (NSURL *) url { TPDrawersFileInfo * new = [[TPDrawersFileInfo alloc] init]; if (new!=nil) { NSFileManager * fileManager = [NSFileManager defaultManager]; NSError * error; NSDictionary * infoDict = [fileManager attributesOfItemAtPath: [url path] error:&error]; id labelValue = nil; [url getResourceValue:&labelValue forKey:NSURLLabelNumberKey error:&error]; new.label = labelValue; new.size = [infoDict objectForKey: @"NSFileSize"]; new.modified = [infoDict objectForKey: @"NSFileModificationDate"]; new.creation = [infoDict objectForKey: @"NSFileCreationDate"]; new.isFile = [NSNumber numberWithBool:[[infoDict objectForKey:@"NSFileType"] isEqualToString:@"NSFileTypeRegular"]]; new.extension = [url pathExtension]; new.filename = [[url lastPathComponent] stringByDeletingPathExtension]; } return new; } Next I have class Folder, which is NSManagesObject subclass // Managed Object class to keep info about folder content @interface Folder : NSManagedObject { NSArray * _files; } @property (nonatomic, retain) NSArray * files; // Array with TPDrawersFileInfo objects @property (nonatomic, retain) NSString * url; // url of folder -(void) reload; //if url changed, load file info again. @end @implementation Folder @synthesize files = _files; @dynamic url; -(void)awakeFromInsert { [self addObserver:self forKeyPath:@"url" options:NSKeyValueObservingOptionNew context:@"url"]; } -(void)awakeFromFetch { [self addObserver:self forKeyPath:@"url" options:NSKeyValueObservingOptionNew context:@"url"]; } -(void)prepareForDeletion { [self removeObserver:self forKeyPath:@"url"]; } -(void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if (context == @"url") { [self reload]; } } -(void) reload { NSMutableArray * result = [NSMutableArray array]; NSError * error = nil; NSFileManager * fileManager = [NSFileManager defaultManager]; NSString * percented = [self.url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]; NSArray * listDir = [fileManager contentsOfDirectoryAtURL: [NSURL URLWithString: percented] includingPropertiesForKeys: [NSArray arrayWithObject: NSURLCreationDateKey ] options:NSDirectoryEnumerationSkipsHiddenFiles error:&error]; if (error!=nil) {NSLog(@"Error <%@> reading <%@> content", error, self.url);} for (id fileURL in listDir) { TPDrawersFileInfo * fi = [TPDrawersFileInfo initWithURL:fileURL]; [result addObject: fi]; } _files = [NSArray arrayWithArray:result]; } @end In app delegate i defined @interface TPAppDelegate : NSObject <NSApplicationDelegate> { IBOutlet NSArrayController * foldersController; Folder * currentFolder; } - (IBAction)chooseDirectory:(id)sender; // choose folder and - (Folder * ) getFolderObjectForPath: path { //gives Folder object if already exist or nil if not ..... } - (IBAction)chooseDirectory:(id)sender { //Opens panel, asking for url NSOpenPanel * panel = [NSOpenPanel openPanel]; [panel setCanChooseDirectories:YES]; [panel setCanChooseFiles:NO]; [panel setMessage:@"Choose folder to show:"]; NSURL * currentDirectory; if ([panel runModal] == NSOKButton) { currentDirectory = [[panel URLs] objectAtIndex:0]; } Folder * folderObject = [self getFolderObjectForPath:[currentDirectory path]]; if (folderObject) { //if exist: currentFolder = folderObject; } else { // create new one Folder * newFolder = [NSEntityDescription insertNewObjectForEntityForName:@"Folder" inManagedObjectContext:self.managedObjectContext]; [newFolder setValue:[currentDirectory path] forKey:@"url"]; [foldersController addObject:newFolder]; currentFolder = newFolder; } [foldersController setSelectedObjects:[NSArray arrayWithObject:currentFolder]]; } Please help ;)

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  • When is a Transient-scope object Deactivated in Ninject?

    - by nwahmaet
    When an object in Ninject is bound with InTransientScope(), the object isn't placed into the cache, since it's, er, transient and not scoped to anything. When done with the object, I can call kernel.Release(obj); this passes through to the Cache where it retrieves the cached item and calls Pipeline.Deactivate using the cached entry. But since transient objects aren't cached, this doesn't happen. I haven't been able to figure out where (or who) performs the deactivation for transient objects. Or is the assumption that transient objects are only ever activated, and that if I want a deactivateable object, I need to use some other scope?

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  • When I mark a property as transient, does the type matter?

    - by mystify
    For example, I make a fullName property and set it to transient. Does it matter what data type that property is, in this case? For example, does it matter if it's set to int or string? As far as I get it, a transient property is almost "ignored" by Core Data. I make my accessors for that and when someone accesses fullName, I simply construct a string and return that. Did I miss something?

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  • If I create a transient property in the model, isn't this managed by core data then?

    - by mystify
    Just to grok this: If I had a transient property, lets say averagePrice, and I mark that as "transient" in the data modeler: This will not be persistet, and no column will be created in SQLite for that? And: If I make my own NSManagedObject subclass with an averagePrice property, does it make any sense to model that property in the xcdatamodel file? Would it make a difference if I would simply create a property in my subclass and not model that in the entity? (I think: yes, it doesn't matter at all ... but not sure)

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  • Troubleshooting transient Windows I/O "The parameter is incorrect." errors

    - by Kevin
    We have a set of .Net 2.0 applications running on Windows 2003 servers which have started experiencing transient "The parameter is incorrect." Windows I/O errors. These errors always happen accessing a file share on a SAN. The fact that this error has happened with multiple applications and multiple servers leads me to believe that this is an infrastructure issue of some sort. The applications all run under the same domain account. When the errors occur they generally will resolve themselves within a few minutes. I can log in to the application server once the error starts occurring and access the file share myself with no problems. I have looked at the Windows event logs and haven't found anything useful. Due to the generic nature of "The parameter is incorrect.", I am looking for additional troubleshooting suggestions for this error. A sample stack trace is below. Note that while this example was during a directory creation operation, when the problem is occurring, this exception is thrown for any file system operations on the share. Exception 1: System.IO.IOException Message: The parameter is incorrect. Method: Void WinIOError(Int32, System.String) Source: mscorlib Stack Trace: at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) at System.IO.Directory.InternalCreateDirectory(String fullPath, String path, DirectorySecurity dirSecurity) at System.IO.Directory.CreateDirectory(String path, DirectorySecurity directorySecurity) at System.IO.Directory.CreateDirectory(String path)

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  • Troubleshooting transient Windows I/O "The parameter is incorrect." errors

    - by Kevin
    We have a set of .Net 2.0 applications running on Windows 2003 servers which have started experiencing transient "The parameter is incorrect." Windows I/O errors. These errors always happen accessing a file share on a SAN. The fact that this error has happened with multiple applications and multiple servers leads me to believe that this is an infrastructure issue of some sort. The applications all run under the same domain account. When the errors occur they generally will resolve themselves within a few minutes. I can log in to the application server once the error starts occurring and access the file share myself with no problems. I have looked at the Windows event logs and haven't found anything useful. Due to the generic nature of "The parameter is incorrect.", I am looking for additional troubleshooting suggestions for this error. A sample stack trace is below. Note that while this example was during a directory creation operation, when the problem is occurring, this exception is thrown for any file system operations on the share. Exception 1: System.IO.IOException Message: The parameter is incorrect. Method: Void WinIOError(Int32, System.String) Source: mscorlib Stack Trace: at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) at System.IO.Directory.InternalCreateDirectory(String fullPath, String path, DirectorySecurity dirSecurity) at System.IO.Directory.CreateDirectory(String path, DirectorySecurity directorySecurity) at System.IO.Directory.CreateDirectory(String path)

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  • NHibernate: How is identity Id updated when saving a transient instance?

    - by bretddog
    If I use session-per-transaction and call: session.SaveOrUpdate(entity) corrected: session.SaveOrUpdateCopy(entity) ..and entity is a transient instance with identity-Id=0. Shall the above line automatically update the Id of the entity, and make the instance persistent? Or should it do so on transaction.Commit? Or do I have to somehow code that explicitly? Obviously the Id of the database row (new, since transient) is autogenerated and saved as some number, but I'm talking about the actual parameter instance here. Which is the business logic instance. EDIT Mappings: public class StoreMap : ClassMap<Store> { public StoreMap() { Id(x => x.Id).GeneratedBy.Identity(); Map(x => x.Name); HasMany(x => x.Staff) // 1:m .Cascade.All(); HasManyToMany(x => x.Products) // m:m .Cascade.All() .Table("StoreProduct"); } } public class EmployeeMap : ClassMap<Employee> { public EmployeeMap() { Id(x => x.Id).GeneratedBy.Identity(); Map(x => x.FirstName); Map(x => x.LastName); References(x => x.Store); // m:1 } } public class ProductMap : ClassMap<Product> { public ProductMap() { Id(x => x.Id).GeneratedBy.Identity(); Map(x => x.Name).Length(20); Map(x => x.Price).CustomSqlType("decimal").Precision(9).Scale(2); HasManyToMany(x => x.StoresStockedIn) .Cascade.All() .Inverse() .Table("StoreProduct"); } } EDIT2 Class definitions: public class Store { public int Id { get; private set; } public string Name { get; set; } public IList<Product> Products { get; set; } public IList<Employee> Staff { get; set; } public Store() { Products = new List<Product>(); Staff = new List<Employee>(); } // AddProduct & AddEmployee is required. "NH needs you to set both sides before // it will save correctly" public void AddProduct(Product product) { product.StoresStockedIn.Add(this); Products.Add(product); } public void AddEmployee(Employee employee) { employee.Store = this; Staff.Add(employee); } } public class Employee { public int Id { get; private set; } public string FirstName { get; set; } public string LastName { get; set; } public Store Store { get; set; } } public class Product { public int Id { get; private set; } public string Name { get; set; } public decimal Price { get; set; } public IList<Store> StoresStockedIn { get; private set; } }

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  • How do I Resolve dependancies that rely on transient context data using castle windsor?

    - by Dan Ryan
    I have a WCF service application that uses a component called EnvironmentConfiguration that holds configuration information for my application. I am converting this service so that it can be used by different applications that have different configuration requirements. I want to identify the configuration to use by allowing an additional parameter to be passed to the service call i.e. public void DoSomething(string originalParameter, string callingApplication) What is the recommended way to alter the behaviour of the EnvironmentConfiguration class based on the transient data (callingApplication) without having to pass the callingApplication variable to all the component methods that need configuration information?

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  • How do I save a transient object that already exists in an NHibernate session?

    - by Daniel T.
    I have a Store that contains a list of Products: var store = new Store(); store.Products.Add(new Product{ Id = 1, Name = "Apples" }; store.Products.Add(new Product{ Id = 2, Name = "Oranges" }; Database.Save(store); Now, I want to edit one of the Products, but with a transient entity. This will be, for example, data from a web browser: // this is what I get from the web browser, this product should // edit the one that's already in the database that has the same Id var product = new Product{ Id = 2, Name = "Mandarin Oranges" }; store.Products.Add(product); Database.Save(store); However, trying to do it this way gives me an error: a different object with the same identifier value was already associated with the session How do I get around this problem?

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  • Is there an difference between transient properties defined in the data model, or in the custom subc

    - by mystify
    I was reading that setting the value of a transient property always results in marking the managed object as "dirty". However, what I don't get is this: If I make a subclass of NSManagedObject and use some extra properties which I don't need to be persistet, how does Core Data know about them and how can it mark the object as dirty when I access these? Again, they're not defined in the data model, so Core Data has no really good hint that they are there. Or does Core Data use some kind of introspection to analyze my custom class and figure out what properties I have in there?

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  • How do I merge a transient entity with a session using Castle ActiveRecordMediator?

    - by Daniel T.
    I have a Store and a Product entity: public class Store { public Guid Id { get; set; } public int Version { get; set; } public ISet<Product> Products { get; set; } } public class Product { public Guid Id { get; set; } public int Version { get; set; } public Store ParentStore { get; set; } public string Name { get; set; } } In other words, I have a Store that can contain multiple Products in a bidirectional one-to-many relationship. I'm sending data back and forth between a web browser and a web service. The following steps emulates the communication between the two, using session-per-request. I first save a new instance of a Store: using (new SessionScope()) { // this is data from the browser var store = new Store { Id = Guid.Empty }; ActiveRecordMediator.SaveAndFlush(store); } Then I grab the store out of the DB, add a new product to it, and then save it: using (new SessionScope()) { // this is data from the browser var product = new Product { Id = Guid.Empty, Name = "Apples" }); var store = ActiveRecordLinq.AsQueryable<Store>().First(); store.Products.Add(product); ActiveRecordMediator.SaveAndFlush(store); } Up to this point, everything works well. Now I want to update the Product I just saved: using (new SessionScope()) { // data from browser var product = new Product { Id = Guid.Empty, Version = 1, Name = "Grapes" }; var store = ActiveRecordLinq.AsQueryable<Store>().First(); store.Products.Add(product); // throws exception on this call ActiveRecordMediator.SaveAndFlush(store); } When I try to update the product, I get the following exception: a different object with the same identifier value was already associated with the session: 00000000-0000-0000-0000-000000000000, of entity:Product" As I understand it, the problem is that when I get the Store out of the database, it also gets the Product that's associated with it. Both entities are persistent. Then I tried to save a transient Product (the one that has the updated info from the browser) that has the same ID as the one that's already associated with the session, and an exception is thrown. However, I don't know how to get around this problem. If I could get access to a NHibernate.ISession, I could call ISession.Merge() on it, but it doesn't look like ActiveRecordMediator has anything similar (SaveCopy threw the same exception). Does anyone know the solution? Any help would be greatly appreciated!

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  • Using Unity – Part 3

    - by nmarun
    The previous blog was about registering and invoking different types dynamically. In this one I’d like to show how Unity manages/disposes the instances – say hello to Lifetime Managers. When a type gets registered, either through the config file or when RegisterType method is explicitly called, the default behavior is that the container uses a transient lifetime manager. In other words, the unity container creates a new instance of the type when Resolve or ResolveAll method is called. Whereas, when you register an existing object using the RegisterInstance method, the container uses a container controlled lifetime manager - a singleton pattern. It does this by storing the reference of the object and that means so as long as the container is ‘alive’, your registered instance does not go out of scope and will be disposed only after the container either goes out of scope or when the code explicitly disposes the container. Let’s see how we can use these and test if something is a singleton or a transient instance. Continuing on the same solution used in the previous blogs, I have made the following changes: First is to add typeAlias elements for TransientLifetimeManager type: 1: <typeAlias alias="transient" type="Microsoft.Practices.Unity.TransientLifetimeManager, Microsoft.Practices.Unity"/> You then need to tell what type(s) you want to be transient by nature: 1: <type type="IProduct" mapTo="Product2"> 2: <lifetime type="transient" /> 3: </type> 4: <!--<type type="IProduct" mapTo="Product2" />--> The lifetime element’s type attribute matches with the alias attribute of the typeAlias element. Now since ‘transient’ is the default behavior, you can have a concise version of the same as line 4 shows. Also note that I’ve changed the mapTo attribute from ‘Product’ to ‘Product2’. I’ve done this to help understand the transient nature of the instance of the type Product2. By making this change, you are basically saying when a type of IProduct needs to be resolved, Unity should create an instance of Product2 by default. 1: public string WriteProductDetails() 2: { 3: return string.Format("Name: {0}<br/>Category: {1}<br/>Mfg Date: {2}<br/>Hash Code: {3}", 4: Name, Category, MfgDate.ToString("MM/dd/yyyy hh:mm:ss tt"), GetHashCode()); 5: } Again, the above change is purely for the purpose of making the example more clear to understand. The display will show the full date and also displays the hash code of the current instance. The GetHashCode() method returns an integer when an instance gets created – a new integer for every instance. When you run the application, you’ll see something like the below: Now when you click on the ‘Get Product2 Instance’ button, you’ll see that the Mfg Date (which is set in the constructor) and the Hash Code are different from the one created on page load. This proves to us that a new instance is created every single time. To make this a singleton, we need to add a type alias for the ContainerControlledLifetimeManager class and then change the type attribute of the lifetime element to singleton. 1: <typeAlias alias="singleton" type="Microsoft.Practices.Unity.ContainerControlledLifetimeManager, Microsoft.Practices.Unity"/> 2: ... 3: <type type="IProduct" mapTo="Product2"> 4: <lifetime type="singleton" /> 5: </type> Running the application now gets me the following output: Click on the button below and you’ll see that the Mfg Date and the Hash code remain unchanged => the unity container is storing the reference the first time it is created and then returns the same instance every time the type needs to be resolved. Digging more deeper into this, Unity provides more than the two lifetime managers. ExternallyControlledLifetimeManager – maintains a weak reference to type mappings and instances. Unity returns the same instance as long as the some code is holding a strong reference to this instance. For this, you need: 1: <typeAlias alias="external" type="Microsoft.Practices.Unity.ExternallyControlledLifetimeManager, Microsoft.Practices.Unity"/> 2: ... 3: <type type="IProduct" mapTo="Product2"> 4: <lifetime type="external" /> 5: </type> PerThreadLifetimeManager – Unity returns a unique instance of an object for each thread – so this effectively is a singleton behavior on a  per-thread basis. 1: <typeAlias alias="perThread" type="Microsoft.Practices.Unity.PerThreadLifetimeManager, Microsoft.Practices.Unity"/> 2: ... 3: <type type="IProduct" mapTo="Product2"> 4: <lifetime type="perThread" /> 5: </type> One thing to note about this is that if you use RegisterInstance method to register an existing object, this instance will be returned for every thread, making this a purely singleton behavior. Needless to say, this type of lifetime management is useful in multi-threaded applications (duh!!). I hope this blog provided some basics on lifetime management of objects resolved in Unity and in the next blog, I’ll talk about Injection. Please see the code used here.

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  • How to make a mapped field inherited from a superclass transient in JPA?

    - by Russ Hayward
    I have a legacy schema that cannot be changed. I am using a base class for the common features and it contains an embedded object. There is a field that is normally mapped in the embedded object that needs to be in the persistence id for only one (of many) subclasses. I have made a new id class that includes it but then I get the error that the field is mapped twice. Here is some example code that is much simplified to maintain the sanity of the reader: @MappedSuperclass class BaseClass { @Embedded private Data data; } @Entity class SubClass extends BaseClass { @EmbeddedId private SubClassId id; } @Embeddable class Data { private int location; private String name; } @Embeddable class SubClassId { private int thingy; private int location; } I have tried @AttributeOverride but I can only get it to rename the field. I have tried to set it to updatable = false, insertable = false but this did not seem to work when used in the @AttributeOverride annotation. See answer below for the solution to this issue. I realise I could change the base class but I really do not want to split up the embedded object to separate the shared field as it would make the surrounding code more complex and require some ugly wrapping code. I could also redesign the whole system for this corner case but I would really rather not. I am using Hibernate as my JPA provider.

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  • Sorting: TransientVO Vs Query/EO based VO

    - by Vijay Mohan
    In ADF, you can do a sorting on VO rows by invoking setSortBy("VOAttrName") API, but the tricky part is that, this API actually appends a clause to VO query at runtime and the actual sorting is performed after doing VO.executeQuery(), this goes fine for Query/EO based VO. But, how about the transient VO, wherein the rows are populated programmatically..?There is a way to it..:)you can actually specify the query mode on your transient VO, so that the sorting happens on already populated VO rows.Here are the steps to go about it..//Populate your transient VO rows.//VO.setSortBy("YourVOAttrName");//VO.setQueryMode(ViewObject.QUERY_MODE_SCAN_VIEW_ROWS);//VO.executeQuery();So, here the executeQuery() is actually the trigger which calls for VO rows sorting.QUERY_MODE_SCAN_VIEW_ROWS flag makes sure that the sorting is performed on the already populated VO cache.

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  • How would you gather client's data on Google App Engine without using Datastore/Backend Instances too much?

    - by ruslan
    I'm relatively new to StackExchange and not sure if it's appropriate place to ask design question. Site gives me a hint "The question you're asking appears subjective and is likely to be closed". Please let me know. Anyway.. One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting? Thank you very much in advance for your thoughts.

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  • How can I gather client's data on Google App Engine without using Datastore/Backend Instances too much?

    - by ruslan
    One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting?

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  • Lesser Known NHibernate Session Methods

    - by Ricardo Peres
    The NHibernate ISession, the core of NHibernate usage, has some methods which are quite misunderstood and underused, to name a few, Merge, Persist, Replicate and SaveOrUpdateCopy. Their purpose is: Merge: copies properties from a transient entity to an eventually loaded entity with the same id in the first level cache; if there is no loaded entity with the same id, one will be loaded and placed in the first level cache first; if using version, the transient entity must have the same version as in the database; Persist: similar to Save or SaveOrUpdate, attaches a maybe new entity to the session, but does not generate an INSERT or UPDATE immediately and thus the entity does not get a database-generated id, it will only get it at flush time; Replicate: copies an instance from one session to another session, perhaps from a different session factory; SaveOrUpdateCopy: attaches a transient entity to the session and tries to save it. Here are some samples of its use. ISession session = ...; AuthorDetails existingDetails = session.Get<AuthorDetails>(1); //loads an entity and places it in the first level cache AuthorDetails detachedDetails = new AuthorDetails { ID = existingDetails.ID, Name = "Changed Name" }; //a detached entity with the same ID as the existing one Object mergedDetails = session.Merge(detachedDetails); //merges the Name property from the detached entity into the existing one; the detached entity does not get attached session.Flush(); //saves the existingDetails entity, since it is now dirty, due to the change in the Name property AuthorDetails details = ...; ISession session = ...; session.Persist(details); //details.ID is still 0 session.Flush(); //saves the details entity now and fetches its id ISessionFactory factory1 = ...; ISessionFactory factory2 = ...; ISession session1 = factory1.OpenSession(); ISession session2 = factory2.OpenSession(); AuthorDetails existingDetails = session1.Get<AuthorDetails>(1); //loads an entity session2.Replicate(existingDetails, ReplicationMode.Overwrite); //saves it into another session, overwriting any possibly existing one with the same id; other options are Ignore, where any existing record with the same id is left untouched, Exception, where an exception is thrown if there is a record with the same id and LatestVersion, where the latest version wins SyntaxHighlighter.config.clipboardSwf = 'http://alexgorbatchev.com/pub/sh/2.0.320/scripts/clipboard.swf'; SyntaxHighlighter.brushes.CSharp.aliases = ['c#', 'c-sharp', 'csharp']; SyntaxHighlighter.all();

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  • Control serialization of GWT

    - by Phuong Nguyen de ManCity fan
    I want GWT to not serialize some fields of my object (which implements Serializable interface). Normally, transient keyword would be enough. However, I also need to put the object on memcache. The use of transient keyword would make the field not being stored on memcache also. Is there any GWT-specific technique to tell the serializer to not serialize a field?

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  • Duplicate DNS Zones (Error 4515 in Event Log )

    - by Campo
    I am getting these two error in the DNS Event log (errors at end of question). I have confirmed I do have duplicate zones. I am wondering which ones to delete. The DomainDNSZone contains all of our DNS records but it does not have the _msdcs zone.... that is in the ForestDNSZone with the duplicates that are not in use. here is a picture of that 3 Questions. I understand the advantages of having DNS in the ForestDNSZone. so... Why is DNS using the DomainDNSZone and is that acceptable considering _msdcs... is in the ForestDNSZone? If so, should I just delete the DC=1.168.192.in-addr.arpa and DC=supernova.local from the ForestDNSZone? Or should I try to get those to be the ones in use? What are those steps? I understand how to delete. That is simple but if i must move zones some info would be appreaciated there. Just to confirm. from my understanding. I can delete the two duplicates in the ForestDNSZone and leave the _msdcs.supernova.local as thats required there. This will resolve the erros I see. Just fyi when I look in those folders from the ForestDNSZone they have just 2 and 1 entries respectively. So obviously not in use compared to the others. I am pretty sure I understand the steps to complete this. But if you would like to provide that info, bonus points! Event Type: Warning Event Source: DNS Event Category: None Event ID: 4515 Date: 1/4/2011 Time: 2:14:18 PM User: N/A Computer: STANLEY Description: The zone 1.168.192.in-addr.arpa was previously loaded from the directory partition DomainDnsZones.supernova.local but another copy of the zone has been found in directory partition ForestDnsZones.supernova.local. The DNS Server will ignore this new copy of the zone. Please resolve this conflict as soon as possible. If an administrator has moved this zone from one directory partition to another this may be a harmless transient condition. In this case, no action is necessary. The deletion of the original copy of the zone should soon replicate to this server. If there are two copies of this zone in two different directory partitions but this is not a transient caused by a zone move operation then one of these copies should be deleted as soon as possible to resolve this conflict. To change the replication scope of an application directory partition containing DNS zones and for more details on storing DNS zones in the application directory partitions, please see Help and Support. For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp. Data: 0000: 89 25 00 00 %.. AND Event Type: Warning Event Source: DNS Event Category: None Event ID: 4515 Date: 1/4/2011 Time: 2:14:18 PM User: N/A Computer: STANLEY Description: The zone supernova.local was previously loaded from the directory partition DomainDnsZones.supernova.local but another copy of the zone has been found in directory partition ForestDnsZones.supernova.local. The DNS Server will ignore this new copy of the zone. Please resolve this conflict as soon as possible. If an administrator has moved this zone from one directory partition to another this may be a harmless transient condition. In this case, no action is necessary. The deletion of the original copy of the zone should soon replicate to this server. If there are two copies of this zone in two different directory partitions but this is not a transient caused by a zone move operation then one of these copies should be deleted as soon as possible to resolve this conflict. To change the replication scope of an application directory partition containing DNS zones and for more details on storing DNS zones in the application directory partitions, please see Help and Support. For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp. Data: 0000: 89 25 00 00 %..

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  • In NHIbernate, why does SaveOrUpdate() update the Version, but SaveOrUpdateCopy() doesn't?

    - by Daniel T.
    I have a versioned entity, and this is what happens when I use SaveOrUpdate() vs. SaveOrUpdateCopy(): // create new entity var entity = new Entity{ Id = Guid.Empty }); Console.WriteLine(entity.Version); // prints out 0 // save the new entity GetNewSession(); entity.SaveOrUpdate(); Console.WriteLine(entity.Version); // prints out 1 GetNewSession(); // loads the persistent entity into the session, so we have to use // SaveOrUpdateCopy() to merge the following transient entity var dbEntity = Database.GetAll<Entity>(); // new, transient entity used to update the persistent entity in the session var newEntity = new Entity{ Id = Guid.Empty }); newEntity.SaveOrUpdateCopy(); Console.WriteLine(entity.Version); // prints out 1, but should be 2 Why is the version number is not updated for SaveOrUpdateCopy()? As I understand it, the transient entity is merged with the persistent entity. The SQL calls confirm that the data is updated. At this point, shouldn't newEntity become persistent, and the version number incremented?

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  • How to use a int2 database-field as a boolean in Java using JPA/Hibernate

    - by mg
    Hello... I write an application based on an already existing database (postgreSQL) using JPA and Hibernate. There is a int2-column (activeYN) in a table, which is used as a boolean (0 = false (inactive), not 0 = true (active)). In the Java application i want to use this attribute as a boolean. So i defined the attribute like this: @Entity public class ModelClass implements Serializable { /*..... some Code .... */ private boolean active; @Column(name="activeYN") public boolean isActive() { return this.active; } /* .... some other Code ... */ } But there ist an exception because Hibernate expects an boolean database-field and not an int2. Can i do this mapping i any way while using a boolean in java?? I have a possible solution for this, but i don't really like it: My "hacky"-solution is the following: @Entity public class ModelClass implements Serializable { /*..... some Code .... */ private short active_USED_BY_JPA; //short because i need int2 /** * @Deprecated this method is only used by JPA. Use the method isActive() */ @Column(name="activeYN") public short getActive_USED_BY_JPA() { return this.active_USED_BY_JPA; } /** * @Deprecated this method is only used by JPA. * Use the method setActive(boolean active) */ public void setActive_USED_BY_JPA(short active) { this.active_USED_BY_JPA = active; } @Transient //jpa will ignore transient marked methods public boolean isActive() { return getActive_USED_BY_JPA() != 0; } @Transient public void setActive(boolean active) { this.setActive_USED_BY_JPA = active ? -1 : 0; } /* .... some other Code ... */ } Are there any other solutions for this problem? The "hibernate.hbm2ddl.auto"-value in the hibernate configuration is set to "validate". (sorry, my english is not the best, i hope you understand it anyway)..

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