How do I find the size of my Core Data persistent store and the free space on the file system?

I am working on a database application using the Core Data开发者_运维问答 framework. In this application I need to display how much data the application currently is using on the iPhone. Is there any way to do this?

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I found this answer on the Apple Dev Forums to be useful for finding disk space available on the apps' home directory partition (note there are currently two partitions on each device).

Use NSPersistentStoreCoordinator to get your store collection.

Use NSFileManager to get each stores' size in bytes (unsigned long long)

NSArray *allStores = [self.persistentStoreCoordinator persistentStores];
unsigned long long totalBytes = 0;
NSFileManager *fileManager = [NSFileManager defaultManager];
for (NSPersistentStore *store in allStores) {
    if (![store.URL isFileURL]) continue; // only file URLs are compatible with NSFileManager
    NSString *path = [[store URL] path];
    DebugLog(@"persistent store path: %@",path);
    // NSDictionary has a category to assist with NSFileManager attributes
    totalBytes += [[fileManager attributesOfItemAtPath:path error:NULL] fileSize];
}

Note that the code above is in a method of my app delegate, and it has a property persistentStoreCoordinator.

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Your persistent store in Core Data is just a file on the file system. You access and possibly create this file when you create your Core Data stack. The following code will print the size of a persistent store and the free space of the file system, in bytes:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *persistentStorePath = [documentsDirectory stringByAppendingPathComponent:@"persistentstore.sqlite"];

NSError *error = nil;
NSDictionary *fileAttributes = [[NSFileManager defaultManager] attributesOfItemAtPath:persistentStorePath error:&error];
NSLog(@"Persistent store size: %@ bytes", [fileAttributes objectForKey:NSFileSize]);

NSDictionary *fileSystemAttributes = [[NSFileManager defaultManager] attributesOfFileSystemForPath:persistentStorePath error:&error];
NSLog(@"Free space on file system: %@ bytes", [fileSystemAttributes objectForKey:NSFileSystemFreeSize]);

This assumes that your persistent store is named persistentstore.sqlite and is stored in the documents directory for your application. If you are uncertain as to the name of your persistent store, look for where you alloc and init your NSPersistentStoreCoordinator. The name of the store should be specified somewhere in the code around there.

Note that the values you get back from the file and file system attributes dictionaries are NSNumbers, so you'll need to convert them to scalar types if you want to work with the file sizes in that manner. One thing to be careful of is that these values are in bytes, so for multi-gigabyte filesystems you might run into number size limitations with 32-bit integer data types.

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Not sure where I saw it, but I believe that removing entries from the database will not necessarily shrink the database file. SQLite reclaims the storage internally and re-uses it. (This is typical of RDBMSs.) I believe there's a command-line utility somewhere that will compact it, but that's not going to help you if your app wants shrink the file to the dataset (to reclaim space for the OS, for example).

So while the file size method will give you a sense of the high-water-mark size of the database, it's not necessarily going to tell you the amount of storage used by your dataset.