[ios开发基础之CoreData[4]]CoreData深入分析篇

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

#pragma mark - Core Data stack

- (NSManagedObjectContext *)managedObjectContext
{
...
return __managedObjectContext;
}

- (NSManagedObjectModel *)managedObjectModel
{
...
return __managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
...
return __persistentStoreCoordinator;
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
self.title = NSLocalizedString(@"Master", @"Master");
id delegate = [[UIApplication sharedApplication] delegate];
self.managedObjectContext = [delegate managedObjectContext];
}
return self;
}

- (NSFetchedResultsController *)fetchedResultsController
{
// 如果查询结果已经存在就直接返回__fetchedResultsController
if (__fetchedResultsController != nil)
{
return __fetchedResultsController;
}

// 1.创建NSFetchRequest对象（相当于SQL语句）
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

// 2.创建查询实体（相当于设置查询哪个表）
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

// 设置获取数据的批数.
[fetchRequest setFetchBatchSize:20];

// 3.创建排序描述符，（ascending：是否升序）
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timeStamp" ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

[fetchRequest setSortDescriptors:sortDescriptors];

// 根据fetchRequest和managedObjectContext来创建aFetchedResultsController对象，并设置缓存名字为"Master".
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"];

// 设置aFetchedResultsController的委托对象为当前类
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;

NSError *error = nil;
// 获取第一批数据
if (![self.fetchedResultsController performFetch:&error])
{
// 错误处理
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}

return __fetchedResultsController;
}

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
[self.tableView beginUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
switch(type)
{
case NSFetchedResultsChangeInsert:
[self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;

case NSFetchedResultsChangeDelete:
[self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;
}
}

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
UITableView *tableView = self.tableView;

switch(type)
{

case NSFetchedResultsChangeInsert:
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;

case NSFetchedResultsChangeDelete:
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
break;

case NSFetchedResultsChangeUpdate:
[self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
break;

case NSFetchedResultsChangeMove:
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
break;
}
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
[self.tableView endUpdates];
}

- (void)insertNewObject
{
// 从NSFetchedResultsController中获取NSManagedObjectContext对象
NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];

// 从NSFetchedResultsController中获取实体描述
NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];

// 在被管理上下文中插入一个新的NSManagedObject
NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];

// 字段赋值
[newManagedObject setValue:[NSDate date] forKey:@"timeStamp"];

// 保存被管理对象上下文，这样刚才的newManagedObject就被保存了
NSError *error = nil;
if (![context save:&error])
{
// 错误处理.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}

// 从NSFetchedResultsController中获取NSManagedObjectContext对象
NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];

// 从被管理对象上下文中删除MO对象
[context deleteObject:[self.fetchedResultsController objectAtIndexPath:indexPath]];

// 保存被管理对象上下文
NSError *error = nil;
if (![context save:&error])
{
// 错误处理
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}