ios - 复制 Realm 文件似乎会导致 Realm 迁移 block 调用 - 为什么？

Question

将 .realm 文件从 folder-location1 复制到 folder-location2(并使用 NSFileManager 将其名称从 location1.realm 更改为 location2.realm)之后 - 似乎在这样做之后，第一次调用这个新文件导致迁移 block 调用! (即 setSchemaVersion)。我想知道为什么 ？？？

之前对“location1/location1.realm”文件的调用不会导致迁移 block 调用 - 但是对“location2/location2.realm”的调用会 - 并且文件结构相同(至少在 Realm-Browser 中没有明显区别)!!

这是我的代码:

    ApplicatonSuppPathHandler *ApplicationSupportPathHandler = [[ApplicatonSuppPathHandler alloc] init];

    // creation of location where this directory shall be placed on the iPhone
    // typically /library/Application Support/<bundleID_name>/RLMGeneralDatabasesFolderName/...
    // = name of directory that the .realm-File finally should be placed in
    NSString *RLMLocation1DirectoryName = folderName;

    // if it does not exist already, create the RLMLocation_xyz-directory (.../library/Application Support/<bundleID_name>/RLMDatabasesFolderName)
    if([ApplicationSupportPathHandler getURLToApplicationDirectoryWithSubDirectory:RLMLocation1DirectoryName] == nil) {
        [ApplicationSupportPathHandler createSubDirectoryAtLocationToApplicationDirectory:RLMLocation1DirectoryName];
    }

    // get the name of entire directory just created
    NSURL *RLMLocation1Directory = [ApplicationSupportPathHandler getURLToApplicationDirectoryWithSubDirectory:RLMLocation1DirectoryName];

    // name of entire path-name (including filename !! ...needed for copy function below...)
    NSString *RLMLocation1Path = [[RLMLocation1Directory path]  stringByAppendingPathComponent:fileName];

    // HERE IS WHERE THE MIGRATION BLOCK IS CALLED - WHY ?????
    // *******************************************************
    RLMRealm *realm_Location1 = [RLMRealm realmWithPath:RLMLocation1Path]; // pointing to realm file at path


    // the rest does work after the migration-block call...
    [realm_Location1 beginWriteTransaction];
    [realm_Location1 deleteAllObjects]; 
    [realm_Location1 addObject:RLMTopoRes];
    [realm_Location1 commitWriteTransaction];

下面是使用的 ApplicationSuppPathHandler 类方法的实现:

@implementation ApplicatonSuppPathHandler

- (NSURL*)getURLToApplicationDirectoryWithSubDirectory:(NSString*)SubDirectoryName {

NSString* appBundleID = [[NSBundle mainBundle] bundleIdentifier];
NSFileManager*fm = [NSFileManager defaultManager];
NSURL* dirPath = nil;

// Find the application support directory in the home directory.
NSArray* appSupportDir = [fm URLsForDirectory:NSApplicationSupportDirectory
                                    inDomains:NSUserDomainMask];
if ([appSupportDir count] > 0)
{
    // Append the bundle ID and the location-Foldername to the URL for the Application Support directory
    dirPath = [[[appSupportDir objectAtIndex:0] URLByAppendingPathComponent:appBundleID] URLByAppendingPathComponent:SubDirectoryName];

    BOOL isDir;
    BOOL exists = [fm fileExistsAtPath:[dirPath path] isDirectory:&isDir];
    if (exists) {
        /* file exists */
        if (isDir) {
            /* path exists */
            return dirPath;
        }
        else {
            NSLog(@"Directory does not exist");
            return nil;
        }
    }
    else {
        /* file does not exist */
        return nil;
    }
}
return dirPath;
}

- (void)createSubDirectoryAtLocationToApplicationDirectory:(NSString*)SubDirectoryName {

NSString* appBundleID = [[NSBundle mainBundle] bundleIdentifier];
NSFileManager*fm = [NSFileManager defaultManager];
NSURL* dirPath = nil;

// Find the application support directory in the home directory.
NSArray* appSupportDir = [fm URLsForDirectory:NSApplicationSupportDirectory
                                    inDomains:NSUserDomainMask];
if ([appSupportDir count] > 0)
{
    // Append the bundle ID and the location-Foldername to the URL for the Application Support directory
    dirPath = [[[appSupportDir objectAtIndex:0] URLByAppendingPathComponent:appBundleID] URLByAppendingPathComponent:SubDirectoryName];

    // If the directory does not exist, this method creates it.
    // This method call works in OS X 10.7 and later only.
    NSError* theError = nil;
    if (![fm createDirectoryAtURL:dirPath withIntermediateDirectories:YES attributes:nil error:&theError]) {
        // Handle the error.
        NSLog(@"%@", theError.localizedDescription);
    }
    else {
        // Mark the directory as excluded from iCloud backups
        if (![dirPath setResourceValue:@YES
                                forKey:NSURLIsExcludedFromBackupKey
                                 error:&theError]) {
            NSLog(@"Error excluding %@ from iCloud backup %@", [dirPath lastPathComponent], theError.localizedDescription);
        }
        else {
            // NSLog(@"Location Directory excluded from iClud backups");
        }
    }
}
}

Answer 1

之前 Realm 中有一个错误，新的 Realm 文件会将其模式版本设置为 0 而不是当前模式版本，这会在您的情况下触发迁移。

上周 Realm 的 master 分支修复了这个问题:https://github.com/realm/realm-cocoa/pull/1142

Building Realm from master 应该可以解决您遇到的问题。 Realm v0.88.0 将随此修复很快发布。