In our application, we often need to do
core data migration when we create a new release. To do this we first need to
get the metadata from our app’s persistent store, so that it can be migrated. We use the
following line of code for this:
[NSPersistentStoreCoordinator
metadataForPersistentStoreOfType:NSSQLiteStoreType URL:self.storeURL
error:&error];
However, we noticed that after restarting the
iPhone, our application wasn’t able to run. We discovered this error in the
log:
Error Domain=NSCocoaErrorDomain Code=256
"The operation couldn’t be completed. (Cocoa error 256.)"
UserInfo=0x146570e0 {NSUnderlyingException=error during prepareSQL for SQL
string 'SELECT TBL_NAME FROM SQLITE_MASTER WHERE TBL_NAME = 'Z_METADATA'' :
attempt to write a readonly database, NSSQLiteErrorDomain=264}
We determined that this is a core data bug,
if you do not need to call metadataForPersistentStoreOfType you won’t see that
there is a problem. We noticed that this
bug occurs only if we use WAL journal mode in SQLite, when we changed it to
DELETE journal mode the app worked as expected.
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