2010年5月7日星期五

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)
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