Core Data CRUD 新增、刪除、修改、查詢 (create save delete update select read query)

1. 插入 新增 存檔 create add save

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…
 
}

2. 查詢 query select read

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];

3. 刪除 delete destroy remove

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
 
}

//屬性

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  查詢 或 修改
NSManagedObject *child = [NSEntityDescription insertNewObjectForEntityForName: @"Person" inManagedObjectContext:thePerson.managedObjectContext];
NSMutableSet *children = [person mutableSetValueForKey:@"children"]; //查詢，可修改
[children addObject:child];
[children removeObject:childToBeRemoved];
[[children managedObjectContext] deleteObject:childToBeRemoved]; //真正的刪除


NSSet *children = [person valueForKey:@"children"]; //查詢，不可修改
for (NSManagedObject *oneChild in children) {
 
    // do something
 
}

補充：

1 是否將圖片存儲到Core Data中，以及NSData如何存儲的一些規則

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