Core数据布尔键值更改未反映在提取中 [英] Core Data boolean key value change not reflected in fetch

问题描述

给定一个NSManagedObject子类的布尔属性删除（这是用两种不同的方式用下面的代码演示，因为两种方法都不工作）：

代码清单1]

  @interface MyManagedObject：NSManagedObject 
 
 @property保留）NSNumber * deleted; 
 //或@property（nonatomic）BOOL deleted;创建并插入到Core Data中的
 
 @end 
  

[代码清单2]

 元数据.deleted = [NSNumber numberWithBool：NO]; 
 // metadata.deleted = NO; 
  

并提取

代码清单3]

  //设置实体描述
 NSEntityDescription * entityDescription = [self entityDescription]; 
 
 //设置排序器
 NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey：@createdAtascending：YES]; 
 NSSortDescriptor * sortDescriptorSection = [[NSSortDescriptor alloc] initWithKey：@myManagedObject.category.titleascending：YES]; 
 
 //构建请求
 NSFetchRequest * request = [[NSFetchRequest alloc] init]; 
 [request setEntity：entityDescription]; 
 [request setSortDescriptors：[NSArray arrayWithObjects：sortDescriptorSection，sortDescriptor，nil]]; 
 [request setPredicate：[NSPredicate predicateWithFormat：@deleted ==％@，[NSNumber numberWithBool：NO]]]; 
 
 //获取请求
 NSArray * items = [[self managedObjectContext] executeFetchRequest：request error：nil]; 
  

返回items数组中的一个项目。

  MyManagedObject * myManagedObject; //假设已初始化
 myManagedObject.deleted = [NSNumber numberWithBool：YES]; 
 // myManagedObject.deleted = YES; 
 
 //在调试器中打印myManagedObject的描述显示deleted = 0在这一点
 
 [myManagedObject.managedObjectContext save：nil]; 
 
 //在调试器中打印myManagedObject的描述仍然显示deleted = 0在这一点
 
 BOOL testValue = myManagedObject.deleted; 
 if（testValue）{
 NSLog（@value updated）; //此行被执行
} 
  

重新执行代码清单3仍然会产生一个项目在items数组中，即使在NSFetchResultsController观察数据库已触发更新之后。如果应用程序被终止并重新启动，重新执行代码清单3不会在项目NSArray中产生任何项目。

解决方案

数据属性已删除与 NSManagedObject 的 isDeleted 属性冲突。

比较核心数据NSPredicate predicateWithBlock和predicateWithFormat在父子上下文用于类似问题和一些实验。

Btw。调用属性更新也会导致问题，比较不能请使用比较Magical Record中的日期的谓词。

Given an NSManagedObject subclass with a boolean property deleted (this is demonstrated in two different ways with code below since both approaches are not working):

[Code Listing 1]

@interface MyManagedObject : NSManagedObject

@property (nonatomic, retain) NSNumber *deleted;
// Or @property (nonatomic) BOOL deleted;

@end

created and inserted into Core Data as follows:

[Code Listing 2]

metadata.deleted = [NSNumber numberWithBool:NO];
// metadata.deleted = NO;

and fetched

[Code Listing 3]

// setup entity description
NSEntityDescription* entityDescription = [self entityDescription];

// setup the sorter
NSSortDescriptor* sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"createdAt" ascending:YES];
NSSortDescriptor* sortDescriptorSection = [[NSSortDescriptor alloc] initWithKey:@"myManagedObject.category.title" ascending:YES];

// Build request
NSFetchRequest* request = [[NSFetchRequest alloc] init];
[request setEntity:entityDescription];
[request setSortDescriptors:[NSArray arrayWithObjects:sortDescriptorSection, sortDescriptor, nil]];
[request setPredicate:[NSPredicate predicateWithFormat:@"deleted == %@", [NSNumber numberWithBool:NO]]];

// Fetch request
NSArray* items = [[self managedObjectContext] executeFetchRequest:request error:nil];

returns one item in the items array as expected. The problem is when deleted is modified:

[Code Listing 4]

MyManagedObject* myManagedObject; // Assume initialized
myManagedObject.deleted = [NSNumber numberWithBool:YES];
// myManagedObject.deleted = YES;

// Printing description of myManagedObject in debugger shows deleted = 0 at this point

[myManagedObject.managedObjectContext save:nil];

// Printing description of myManagedObject in debugger still shows deleted = 0 at this point

BOOL testValue = myManagedObject.deleted;
if (testValue) {
    NSLog(@"value updated"); // This line is executed
}

Re-executing code listing 3 still yields one item in the items array even after a NSFetchResultsController watching the database has fired an update. If the application is terminated and relaunched, re-executing code listing 3 yields no items in the items NSArray.

解决方案

Calling a Core Data property "deleted" conflicts with the isDeleted property of NSManagedObject.

Compare Core Data NSPredicate predicateWithBlock and predicateWithFormat in Parent Child Context for a similar problem and some experiments.

Btw. calling a property "updated" causes also problems, compare Cannot use a predicate that compares dates in Magical Record.

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