Any way to pre populate core data?

问题:

I\'ve been creating a list app and backing it with core data.

I would like to have a default list of say 10 airport\'s items, so that the user doesn\'t have to start from scratch.

Is there any way to do this?

Any help is appreciated. Thanks in advance.

回答1:

Here\'s the best way (and doesn\'t require SQL knowledge):
Create a quick Core Data iPhone app (Or even Mac app) using the same object model as your List app. Write a few lines of code to save the default managed objects you want to the store. Then, run that app in the simulator. Now, go to ~/Library/Application Support/iPhone Simulator/User/Applications. Find your application among the GUIDs, then just copy the sqlite store out into your List app\'s project folder.

Then, load that store like they do in the CoreDataBooks example.

回答2:

Yes there is in fact the CoreDataBooks example does this, you can download the code here: sample code

What you do is create the internal store (database) using the normal procedure to initialize your store just like you would with any other store, then you simply run your code and let it execute the code as described in the CoreDataBooks example (code snippet below). Once the store has been initialized you will want to create a NSManagedObjectContext and initialize it with the created persistent store, insert all the entities you need, and save the context.

Once the context has been successfully saved, you can stop your application, then go to finder and go to folder: ~/Library/Developer type in the search .sqlite and look under /Developer, sorting by date will give you the most recent .sqlite database which should match the time that the code was executed, you can then take this store and add it as a resource of your project. This file then can be read by a persistent store coordinator.

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

if (persistentStoreCoordinator) {
    return persistentStoreCoordinator;
}


NSString *storePath = [[self applicationDocumentsDirectory]      stringByAppendingPathComponent: @\"CoreDataBooks.sqlite\"];
 /*
  Set up the store.
 For the sake of illustration, provide a pre-populated default store.
 */
NSFileManager *fileManager = [NSFileManager defaultManager];
// If the expected store doesn\'t exist, copy the default store.
if (![fileManager fileExistsAtPath:storePath]) {
  NSString *defaultStorePath = [[NSBundle mainBundle] pathForResource:@\"CoreDataBooks\"      ofType:@\"sqlite\"];
 if (defaultStorePath) {
 [fileManager copyItemAtPath:defaultStorePath toPath:storePath error:NULL];
 }
}

NSURL *storeUrl = [NSURL fileURLWithPath:storePath];

 NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber   numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil]; 
  persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel: [self managedObjectModel]];

 NSError *error;
 if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:options error:&error]) {
  // Update to handle the error appropriately.
  NSLog(@\"Unresolved error %@, %@\", error, [error userInfo]);
 exit(-1);  // Fail
}    

return persistentStoreCoordinator;
}

Hope that helps.

-Oscar

回答3:

With this method you don\'t need to make a separate app or have any SQL knowledge. You only need to be able to make a JSON file for your initial data.

I use a JSON file that I parse into objects, then insert them in Core Data. I do this when the app initializes. I also make one entity in my core data that indicates if this initial data is already inserted, after I insert the initial data I set this entity so the next time the script runs it sees that the initial data has already been initialized.

To read json file into objects:

NSString *initialDataFile = [[NSBundle mainBundle] pathForResource:@\"InitialData\" ofType:@\"json\"];
NSError *readJsonError = nil;
NSArray *initialData = [NSJSONSerialization
                        JSONObjectWithData:[NSData dataWithContentsOfFile:initialDataFile]
                        options:kNilOptions
                        error:&readJsonError];

if(!initialData) {
    NSLog(@\"Could not read JSON file: %@\", readJsonError);
    abort();
}

Then you can make entity objects for it like this:

[initialData enumerateObjectsUsingBlock:^(id objData, NSUInteger idx, BOOL *stop) {

    MyEntityObject *obj = [NSEntityDescription
                          insertNewObjectForEntityForName:@\"MyEntity\"
                          inManagedObjectContext:dataController.managedObjectContext];

    obj.name = [objData objectForKey:@\"name\"];
    obj.description = [objData objectForKey:@\"description\"];

    // then insert \'obj\' into Core Data

}];

If you want a more detailed description on how to do this, check out this tutorial: http://www.raywenderlich.com/12170/core-data-tutorial-how-to-preloadimport-existing-data-updated

回答4:

For 10 items, you can just do this within applicationDidFinishLaunching: in your app delegate.

Define a method, say insertPredefinedObjects, that creates and populates the instances of the entity in charge of managing your airport items, and save your context. You may either read the attributes from a file or simply hardwire them in your code. Then, call this method inside applicationDidFinishLaunching:.

回答5:

Bear in mind, when following the CoreDataBooks example code, that it probably breaks the iOS Data Storage Guidelines:

https://developer.apple.com/icloud/documentation/data-storage/

I\'ve had an app rejected for copying the (read-only) pre-populated database to the documents directory - as it then gets backed up to iCloud - and Apple only want that to happen to user-generated files.

The guidelines above offer some solutions, but they mostly boil down to:

• store the DB in the caches directory, and gracefully handle situations where the OS purges the caches - you will have to rebuild the DB, which probably rules it out for most of us.

• set a \'do not cache attribute\' on the DB file, which is a little arcane, as it needs to be done differently for different OS versions.

I don\'t think it is too tricky, but be aware that you have a bit extra to do to make that example code work alongside iCloud...

回答6:

So I have developed a generic method that loads from a dictionary (possibly from JSON) and populates the database. It should be used ONLY with trusted data (from a safe channel), it can\'t handle circular references and schema migrations can be problematic... But for simple use cases like mine it should be fine

Here it goes

- (void)populateDBWithDict:(NSDictionary*)dict
               withContext:(NSManagedObjectContext*)context
{
    for (NSString* entitieName in dict) {

        for (NSDictionary* objDict in dict[entitieName]) {

            NSManagedObject* obj = [NSEntityDescription insertNewObjectForEntityForName:entitieName inManagedObjectContext:context];
            for (NSString* fieldName in objDict) {

                NSString* attName, *relatedClass, *relatedClassKey;

                if ([fieldName rangeOfString:@\">\"].location == NSNotFound) {
                    //Normal attribute
                    attName = fieldName; relatedClass=nil; relatedClassKey=nil;
                } else {
                    NSArray* strComponents = [fieldName componentsSeparatedByString:@\">\"];
                    attName = (NSString*)strComponents[0];
                    relatedClass = (NSString*)strComponents[1];
                    relatedClassKey = (NSString*)strComponents[2];
                }
                SEL selector = NSSelectorFromString([NSString stringWithFormat:@\"set%@:\", attName ]);
                NSMethodSignature* signature = [obj methodSignatureForSelector:selector];
                NSInvocation* invocation = [NSInvocation invocationWithMethodSignature:signature];
                [invocation setTarget:obj];
                [invocation setSelector:selector];

                //Lets set the argument
                if (relatedClass) {
                    //It is a relationship
                    //Fetch the object
                    NSFetchRequest* query = [NSFetchRequest fetchRequestWithEntityName:relatedClass];
                    query.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:relatedClassKey ascending:YES]];
                    query.predicate = [NSPredicate predicateWithFormat:@\"%K = %@\", relatedClassKey, objDict[fieldName]];

                    NSError* error = nil;
                    NSArray* matches = [context executeFetchRequest:query error:&error];


                    if ([matches count] == 1) {
                        NSManagedObject* relatedObject = [matches lastObject];
                        [invocation setArgument:&relatedObject atIndex:2];
                    } else {
                        NSLog(@\"Error! %@ = %@ (count: %d)\", relatedClassKey,objDict[fieldName],[matches count]);
                    }


                } else if ([objDict[fieldName] isKindOfClass:[NSString class]]) {

                    //It is NSString
                    NSString* argument = objDict[fieldName];
                    [invocation setArgument:&argument atIndex:2];
                } else if ([objDict[fieldName] isKindOfClass:[NSNumber class]]) {

                    //It is NSNumber, get the type
                    NSNumber* argument = objDict[fieldName];
                    [invocation setArgument:&argument atIndex:2];

                }
                [invocation invoke];


            }

            NSError *error;
            if (![context save:&error]) {
                NSLog(@\"%@\",[error description]);
            }
        }
    }   
}

And loads from json...

NSString *filePath = [[NSBundle mainBundle] pathForResource:@\"initialDB\" ofType:@\"json\"];
NSData *jsonData = [NSData dataWithContentsOfFile:filePath];

NSError* error;
NSDictionary *initialDBDict = [NSJSONSerialization JSONObjectWithData:jsonData
                                                           options:NSJSONReadingMutableContainers error:&error];

[ self populateDBWithDict:initialDBDict withContext: [self managedObjectContext]];

JSON examples

    {
    \"EntitieA\": [ {\"Att1\": 1 }, {\"Att1\": 2} ],
    \"EntitieB\": [ {\"Easy\":\"AS ABC\", \"Aref>EntitieA>Att1\": 1} ]
    }

and

{
    \"Country\": [{\"Code\": 55, \"Name\": \"Brasil\",\"Acronym\": \"BR\"}],
    \"Region\": [{\"Country>Country>code\": 55, \"Code\": 11, \"Name\": \"Sao Paulo\"},
               {\"Country>Country>code\": 55, \"Code\": 31, \"Name\": \"Belo Horizonte\"}]
}

回答7:

How about check if any objects exist and if not, create one with some data?

NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@\"Settings\"];
_managedObjectSettings = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];

if ([_managedObjectSettings count] == 0) {
    // first time, create some defaults
    NSManagedObject *newDevice = [NSEntityDescription insertNewObjectForEntityForName:@\"Settings\" inManagedObjectContext:managedObjectContext];

    [newDevice setValue:[NSNumber numberWithBool: YES ] forKey:@\"speed\"];
    [newDevice setValue:[NSNumber numberWithBool: YES ] forKey:@\"sound\"];
    [newDevice setValue:[NSNumber numberWithBool: NO ] forKey:@\"aspect\"];
    [newDevice setValue:[NSNumber numberWithBool: NO  ] forKey: @\"useH264\"];
    [newDevice setValue:[NSNumber numberWithBool: NO ] forKey: @\"useThumbnail\"];

    NSError *error = nil;
    // Save the object to persistent store
    if (![managedObjectContext save:&error]) {
        NSLog(@\"Can\'t Save! %@ %@\", error, [error localizedDescription]);
    }
}

回答8:

This answer is only for people who are

• including a pre-populated database in your app
• making an app for multiple platforms (iOS, Android, etc.)

I had made a prepopulated SQLite database for an Android app. Then when I was making an iOS version of the app I thought it would be best to use Core Data. So I spent quite a long time learning Core Data and then rewriting the code to prepopulate the database. Learning how to do every single step in both platforms required lots of research and trial and error. There was a lot less overlap than I would have hoped.

In the end I just decided to use the same SQLite database from my Android project. Then I used the FMDB wrapper to directly access the database in iOS. The benefits:

• Only need to make the prepopulated database once.
• Doesn\'t require a paradigm shift. The syntax between Android and FMDB, while different, is still fairly similar.
• Have a lot more control over how Queries are performed.
• Allows full text search.

Although I don\'t regret learning Core Data, if I were to do it over I could have saved a lot of time by just sticking to SQLite.

If you are starting in iOS and then planning to move to Android, I would still use a SQLite wrapper like FMDB or some other software to prepopulate the database. Although you can technically extract the SQLite database that you prepopulate with Core Data, the schema (table and column names, etc.) will be strangely named.

By the way, if you don\'t need to modify your prepopulated database, then don\'t copy it to the documents directory after the app is installed. Just access it directly from the bundle.

// get url reference to databaseName.sqlite in the bundle
let databaseURL: NSURL = NSBundle.mainBundle().URLForResource(\"databaseName\", withExtension: \"sqlite\")!

// convert the url to a path so that FMDB can use it
let database = FMDatabase(path: databaseURL.path)

This makes it so that you don\'t have two copies.

Update

I now use SQLite.swift rather than FMDB, because it integrates better with Swift projects.

回答9:

Another method for storing defaults is found by way of NSUserDefaults. (surprise!) And its easy.

Suggested by some, put that into the applicationDidFinishLaunching

In the given case of 10 defaults, Airport0 thru 9

Setting

NSUserDefaults *nud = [NSUserDefaults standardUserDefaults];
[nud setString:@\"MACADDRESSORWHY\" forKey:@\"Airport0\"];
    ...
[nud setString:@\"MACADDRESSORWHY\" forKey:@\"Airport9\"];
[nud synchronize];

or

[[NSUserDefaults standardUserDefaults] setString:@\"MACADDRESSORWHY\" forKey:@\"Airport9\"]];
     ...
[[NSUserDefaults standardUserDefaults] synchronize];

And then, getting the defaults.

NSString *air0 = [[NSUserDefaults standardUserDefaults] stringForKey:@\"Airport0\"];