The NSFetchedResultsController is a type of controller provided by the
Core Data framework that helps manage results from queries.
NSFetchedResultsController幫我們管理我們要做的查詢
NSManagedObjectContext is a handle to the application’s persistent store that provides a context, or environment, in which the managed objects can exist.
NSManagedObjectContext 幫我們產生一個存放managed objects的環境，並幫我們處理與persistent store之間的溝通。
//Sample code
NSFetchedResultsController幫我們管理我們要做的查詢
NSManagedObjectContext is a handle to the application’s persistent store that provides a context, or environment, in which the managed objects can exist.
NSManagedObjectContext 幫我們產生一個存放managed objects的環境，並幫我們處理與persistent store之間的溝通。
//Sample code
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController
alloc] initWithFetchRequest:fetchRequest managedObjectContext:
self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
我們來了解一下cacheName這個參數的用法：
如果你不想要cache查詢結果，那直接傳nil給他就好。
如果你傳了cacheName給它，那代表它會在下次搜尋之前，先去檢查上一次的cache有沒有相同的值。
如果有找到相同的查詢，就不進行查詢直接取用它；如果不相同，就刪除上次的cache，然後存放這次的查詢結果供下次使用。
self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
我們來了解一下cacheName這個參數的用法：
如果你不想要cache查詢結果，那直接傳nil給他就好。
如果你傳了cacheName給它，那代表它會在下次搜尋之前，先去檢查上一次的cache有沒有相同的值。
如果有找到相同的查詢，就不進行查詢直接取用它；如果不相同，就刪除上次的cache，然後存放這次的查詢結果供下次使用。
the persistent store 通常在操作 SQLite database
而The managed object model 是persistent store的抽象邏輯表現層。
而The managed object model 是persistent store的抽象邏輯表現層。
Calling the getter for the delegate’s managedObjectContext starts a chain reaction in
which
-(NSManagedObjectContext *)managedObjectContext, calls -(NSPersistentStoreCoordinator *)persistentStoreCoordinator and then in turns calls -(NSManagedObjectModel *)managedObjectModel. The call to managedObjectContext therefore initializes the entire Core Data stack and readies Core Data for use.
//Delete時，有四個規則
-(NSManagedObjectContext *)managedObjectContext, calls -(NSPersistentStoreCoordinator *)persistentStoreCoordinator and then in turns calls -(NSManagedObjectModel *)managedObjectModel. The call to managedObjectContext therefore initializes the entire Core Data stack and readies Core Data for use.
//Delete時，有四個規則
- No action 什麼都不做：Does nothing and lets the related objects think the parent object still exists.
- Nullify 把每個相關連的物件的父物件設為nil：For each related object, sets the parent object property to null.
- Cascade 把所有相關的物件也一併刪除：Deletes each related object.
- Deny 如果仍有相關物件，則禁止delete的動作：Prevents the parent object from being deleted if there is at least one related object.
//NSFetchedResultsController是用來給UITableView使用的
You use a fetched results controller to efficiently manage the results returned from a Core Data fetch request to provide data for a
You use a fetched results controller to efficiently manage the results returned from a Core Data fetch request to provide data for a
UITableView object.
//讀取資料
- (NSArray *) readDataWithEntityName:(NSString *)entityName andPredicate:(NSPredicate *)predicate sortDescriptor:(NSString *)sortDescriptorString asceding:(BOOL)isAsceding{
NSManagedObjectContext *context = [_coreData managedObjectContext];
NSEntityDescription *entityDescription = [NSEntityDescription entityForName:entityName inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];
// Set example predicate and sort orderings...
[request setPredicate:predicate];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]
initWithKey:sortDescriptorString ascending:isAsceding];
[request setSortDescriptors:@[sortDescriptor]];
NSError *error;
NSArray *array = [context executeFetchRequest:request error:&error];
if (array == nil)
{
// Deal with error...
}
return array;
}
#pragma mark Save
- (void)saveContext
{
NSError *error = nil;
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil) {
if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
}
#pragma mark Add
- (void) addNewRecordIntoEntityByName:(NSString *)entityName newObjects:(NSArray *)objects{
NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:entityName inManagedObjectContext:_managedObjectContext];
// If appropriate, configure the new managed object.
// Normally you should use accessor methods, but using KVC here avoids the need to add a custom class to the template.
for (NSDictionary *objectInfo in objects) {
[objectInfo enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
[newManagedObject setValue:obj forKey:key];
}];
}
// Save the context.
NSError *error = nil;
if (![_managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
#pragma mark Delete
[_managedObjectContext deleteObject:managedObject];
NSError *error = nil;
if (![_managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
[_managedObjectContext.undoManager undo];
NSError *error = nil;
if (![_managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
[_managedObjectContext.undoManager redo];
NSError *error = nil;
if (![_managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
#pragma mark Save
- (void)saveContext
{
NSError *error = nil;
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil) {
if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
}
- (void) addNewRecordIntoEntityByName:(NSString *)entityName newObjects:(NSArray *)objects{
// Normally you should use accessor methods, but using KVC here avoids the need to add a custom class to the template.
for (NSDictionary *objectInfo in objects) {
[objectInfo enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
[newManagedObject setValue:obj forKey:key];
}];
}
NSError *error = nil;
if (![_managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
#pragma mark Delete
//刪除指定物件
-(void) deleteRecord:(NSManagedObject *)managedObject{if (![_managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
//恢復上一步
-(void) undoRecord{if (![_managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
//恢復下一步
-(void) redoRecord{if (![_managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
