Merge old Plist with new Plist - objective-c

Question

I have add new entities to existing Plist. New version of app crashes due to Plist inconsistencies.
How do I merge old plist data with new plist?
My Plist creation method is as follows
- (void)createEditableCopyOfFileIfNeeded:(NSString *)plistName
{
// First, test for existence.
BOOL success;
NSFileManager *fileManager = [NSFileManager defaultManager];
NSError *error;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *plistPath = [documentsDirectory stringByAppendingPathComponent:plistName];
success = [fileManager fileExistsAtPath:plistPath];
if (success)
{
return;
}
// The writable database does not exist, so copy the default to the appropriate location.
NSString *defaultPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:plistName];
success = [fileManager copyItemAtPath:defaultPath toPath:plistPath error:&error];
if (!success)
{
NSAssert1(0, #"Failed to create writable database file with message '%#'.", [error localizedDescription]);
}
}
Thanks in advance

Answer 1

I would include a version key in your plist to compare it with the version of the application. You can check the version of your application with the following snippet:
[[NSBundle mainBundle] objectForInfoDictionaryKey:#"CFBundleVersion"]
Then, at the startup of the application:
Read the plist, if there is no version key, it will be old version.
If old version then perform data migration to current version, adding the non-existing keys with default values. Here I would take in account different version numbers for future updates.
Add the version key with the version of your bundle as a value.
Save the plist.

Answer 2

You can do it this way:
Rename old plist e.g. old.plist
Read both plists from separate files
Merge information needed adding chosen information programatically to new plist
Save new plist merged