iphone core data 基础操作

1. 插入 AppDelegate *app = [[UIApplication sharedApplication] delegate]; NSManagedObjectContext *context = [app managedObjectContext]; NSManagedObject ＊newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:@"entityname" inManagedObjectContext:context]; [newManagedObject setValue:value forKey:@"propertyname"]; NSError *error; if (![context save:&error]) { // Handle the error… } //查询 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Hero" inManagedObjectContext:managedObjectContext]; NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@”name” ascending:YES]; NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@”secretIdentity” ascending:YES]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1, sortDescriptor2, nil]; [fetchRequest setSortDescriptors:sortDescriptors]; [fetchRequest setEntity:entity]; [fetchRequest setFetchBatchSize:20]; NSArray *objecs = [context executeFetchRequest: fetchRequest error:&error]; //删除 NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext; [context deleteObject:[objecs objectIndex:index]; // Save the context. NSError *error; if (![context save:&error]) { // Update to handle the error appropriately. NSLog(@”Unresolved error %@, %@”, error, [error userInfo]); exit(-1); // Fail } //属性 NSManagedObject *managedObject; NSString *keypath; NSString *labelString; NSString *currentValue = [self.managedObject valueForKeyPath:self.keypath]; NSEntityDescription *ed = [self.managedObject entity]; NSDictionary *properties = [ed propertiesByName]; NSAttributeDescription *ad = [properties objectForKey:self.keypath]; NSString *defaultValue = nil; if (ad != nil) defaultValue = [ad defaultValue]; //core data relation  查询 或 修改 NSManagedObject *child = [NSEntityDescription insertNewObjectForEntityForName: @"Person" inManagedObjectContext:thePerson.managedObjectContext]; NSMutableSet *children = [person mutableSetValueForKey:@"children"]; //查询，可修改 [children addObject:child]; [children removeObject:childToBeRemoved]; [[children managedObjectContext] deleteObject:childToBeRemoved]; //真正的删除 NSSet *children = [person valueForKey:@"children"]; //查询，不可修改 for (NSManagedObject *oneChild in children) { // do something } 补充： 1 是否将图片存储到Core Data中，以及NSData如何存储的一些规则 First, always store your images in a usable format such as PNG or JPEG instead of NSData. This will save you a lot of headaches. Second, the rule for storing binary data is: < 100kb store in the same table as the relevant data < 1mb store in a separate table attached via a relationship to avoid loading unnecessarily > 1mb store on disk and reference it inside of Core Data (1。图片尽量保存为文件 2。<100k 和相关数据保存在一张表中  <1M保存在单独的一张表中 >1M保存到磁盘文件)

转载于:https://www.cnblogs.com/zsw-1993/archive/2012/10/17/4880786.html