NSPredicate语法以排除给定的NSManagedObject

Question

我有一个Core Data存储,其中许多实体应该是其特定NSEntityDescription的唯一实例.我目前通过为给定的描述创建一个新实体来做到这一点,然后:

-(void)clearMyManagedObjectsExceptFor:(NSManagedObject*)except {

    NSArray *managedObjects = [ self fetchMyManagedObjectsWithPredicateOrNil: nil ];
    // returns all managed objects for a given NSEntityDescription

    NSManagedObject *managedObject;
    for( NSUInteger i = 0; i < [ managedObjects count ]; i++ ){
        managedObject = [ managedObjects objectAtIndex: i ];
        if( ![ managedObject isEqual: except ] ){
            [ managedObjectContext deleteObject: managedObject ];
        }
    }
}

哪个有效,但感觉我应该能够做到这一点!=使用NSPredicate而不是迭代,但我无法弄清楚正确的谓词语法.任何人都可以开导我吗？

Answer 1

你可以这样做:

- (void) clearObjectsExceptFor:(NSManagedObject *)exception {
  NSPredicate * allExcept = [NSPredicate predicateWithFormat:@"SELF != %@", exception];
  NSArray * objects = [self fetchMyManagedObjectsWithPredicateOrNil:allExcept];
  for (NSManagedObject * object in objects) {
    [managedObjectContext deleteObject:object];
  }
}