iOS CoreData primitive accessor-优快云博客

本文探讨了CoreData中原始访问器（primitive accessors）的主要用途及实现方式，特别是如何利用这些访问器来避免不必要的键值观察（KVO）通知开销，并提供了设置默认属性值的具体示例。

　　Given an entity with an attribute firstName, Core Data automatically generates firstName, setFirstName:, primitiveFirstName, and setPrimitiveFirstName.

　　The primary use of primitive accessors is to prevent key-value observing notifications from being sent when you change a value.

　　Sometimes you do not want such notifications sent because they have quite a bit of overhead. E.g. when importing large sets of data or when you use a transitory value to alter a persisted value.

　　In my opinion,

　　You could override the awakeFromInsert method to set a default value for this property;

　　Every time you insert object into managedObjectContext,

　　CoreData framework will call awakeFromInsert method automatically.

　　And in this method,you should use primitive accssor to set the default value.

　　For example,there is a property dueDate in the category's .h file,

　　u can define primitiveDueDate property in the subclass of NSManagedObject.

　　And add @dynamic primitiveDueDate in .m file.

　show u the code:

// a subclass of NSManagedObject

//.h file
@interface Task : NSManagedObject

@property (nonatomic, strong) NSDate *primitiveDueDate;

@end

//.m file
@implementation Task

@dynamic primitiveDueDate;

- (void)awakeFromInsert{
    [super awakeFromInsert];
    
    NSDate *defaultDate = [NSDate dateWithTimeIntervalSinceNow:60*60*24*3]; // 3 days
    
    self.primitiveDueDate = defaultDate;
}

@end

// category file contains a property named dueDate

@interface Task (CoreDataProperties)

@property (nullable, nonatomic, retain) NSDate *dueDate;

@end