How to delete selected tables using persistentStoreCoordinator - ios

Question

I'm currently working on an IOS app which is already developed using objective-C.
I have added a module where users when login store details about the user. But as the app is already having some code, when I press the logout button it deletes all the entities from the database. For this they are using something like the code below.
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSError *error = nil;
// retrieve the store URL
NSURL *storeURL = [[managedObjectContext persistentStoreCoordinator] URLForPersistentStore:[[[managedObjectContext persistentStoreCoordinator] persistentStores] lastObject]];
// lock the current context
[managedObjectContext lock];
[managedObjectContext reset];//to drop pending changes
//delete the store from the current managedObjectContext
if ([[managedObjectContext persistentStoreCoordinator] removePersistentStore:[[[managedObjectContext persistentStoreCoordinator] persistentStores] lastObject] error:&error]){
// remove the file containing the data
[[NSFileManager defaultManager] removeItemAtURL:storeURL error:&error];
//recreate the store like in the appDelegate method
[[managedObjectContext persistentStoreCoordinator] addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error];//recreates the persistent store
}
[managedObjectContext unlock];
By keeping the break points, I understood that they are retrieving the url of the database and deleting it and re-creating it. Lets say they have 3 tables A,B and C, I want to delete A & B but not C. Reference- Persistent Store Coordinator
Is my understanding correct? How can I achieve this?
TIA

Answer 1

Try this code
NSManagedObjectContext *context = [self managedObjectContext];
[context deleteObject:managedObject];
NSError *error = nil;
if (![context save:&error]) {
NSLog(#"Can't Delete! %# %#", error, [error localizedDescription]);
return;
}

Answer 2

When user tap logout, you should clear the stored data.
First of all Fetch all the data using simple fetch store it in an array say "results"
then fetch objects in the array and remove it
for (Entity *entityOBJ in results) {
[context deleteObject:entityOBJ];
}
[context save:&error];
You have 3 tables, repeat it for 3 tables. Create a function just pass on the TableName.

Answer 3

I did something like below. Correct me If I'm wrong with my approach.
- (void) deleteData {
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSError *error = nil;
[managedObjectContext lock];
[managedObjectContext reset];
NSPersistentStoreCoordinator *psc = [managedObjectContext persistentStoreCoordinator];
NSManagedObjectModel *managedModel = [psc managedObjectModel];
NSArray *allEntityNames = [managedModel.entitiesByName allKeys];
for(NSString *entityName in allEntityNames)
{
//I wanted to delete all objects except for one table
if(![entityName isEqual:switchAccountsTableName])
{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init];
NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
NSError *objError = nil;
NSArray *fetchedObjects = [managedObjectContext executeFetchRequest:fetchRequest error:&objError];
if(fetchedObjects == nil)
{
NSLog(#"Logout- Couldnt delete entity objects");
}
for(NSManagedObject *entityObj in fetchedObjects)
{
[managedObjectContext deleteObject:entityObj];
}
}
}
[managedObjectContext save:&error];
[managedObjectContext unlock];
}