Core Data 数据操作 增删改查

所有操作都基于Core Data框架相关 API，工程需要添加CoreData.framework支持

1.增  NSEntityDescription insertNewObjectForEntityForName: inManagedObjectContext:

利用NSEntityDescription工厂方法创建Entity

AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;

//get NSManagedObjectContext
NSManagedObjectContext *context = [appDelegate managedObjectContext];

NSManagedObject *managedObject = nil;

managedObject = [NSEntityDescription insertNewObjectForEntityForName:youEntityName inManagedObjectContext:context];//youEntityName is a NSString

[managedObject setValue:youKeyValue forKey: youEntityKeyName];//KVO方式赋值value - key
//e.g. [managedObject setValue:[name descrition] forKey: @"kEntityKeyName"], the entity must include name property, and its name must be "kEntityKeyName"

[appDelegate saveContext];//Don‘t forget to save the changes

2.删 context deleteObject:

NSManagedObject * deleteObject = youWillDeleteObject;//Can get the object from the query result , which is a NSArray getting by the way of using NSFetchRequest
/*e.g.
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:kEntityName];
NSError *error;
NSArray *objects = [context executeFetchRequest:request error:&error];
//choose one object or many objects
*/

AppDelegate *delegate = [UIApplication sharedApplication].delegate;

NSManagedObjectContext *context = [delegate managedObjectContext];

[context deleteObject:deleteObject];

[delegate saveContext];

3.改 略

4.查

4.1查找全部context executeFetchRequest: error:

NSMutableArray *_array;

AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
NSManagedObjectContext *context = [appDelegate managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:kEntityName];

NSError *error;
NSArray *objects = [context executeFetchRequest:request error:&error];

if (objects == nil) {
    NSLog(@"There is an error!");
}else{
    _array = [NSMutableArray arrayWithArray:objects];
}