核心数据：Keypath“objectID”在实体中找不到 [英] Core Data: Keypath "objectID" not found in entity

问题描述

我使用 NSFetchedResultsController 使用谓词在我的应用程序中加载文档的列表。我想加载除当前有效的文档。

我使用Rentzsch的 MOGenerator 创建一个 _Document 类，然后我把所有我的自定义代码在文档子类中。 _Document 生成类型为 DocumentID 的 objectID 属性。 p>

在创建控制器的类中，我设置控制器的 currentDocID 属性：

  controller.currentDocID = self.document.objectID; 
 

在控制器本身，我延迟加载fetchedResultsController：

   - （NSFetchedResultsController *）fetchedResultsController {
 if（fetchedResultsController！= nil）{
 return fetchedResultsController; 
} 
 
 NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init]; 
 NSEntityDescription * entity = [NSEntityDescription entityForName：@DocumentinManagedObjectContext：managedObjectContext]; 
 [fetchRequest setEntity：entity]; 
 
 NSPredicate * predicate = [NSPredicate predicateWithFormat：@（objectID！=％@），self.currentDocID]; 
 [fetchRequest setPredicate：predicate]; 
 
 NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey：@dateModifiedascending：NO]; 
 NSArray * sortDescriptors = [[NSArray alloc] initWithObjects：sortDescriptor，nil]; 
 
 [fetchRequest setSortDescriptors：sortDescriptors]; 
 
 NSFetchedResultsController * aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest managedObjectContext：managedObjectContext sectionNameKeyPath：nil cacheName：@Root]; 
 aFetchedResultsController.delegate = self; 
 self.fetchedResultsController = aFetchedResultsController; 
 
 [aFetchedResultsController release]; 
 [sortDescriptor release]; 
 [sortDescriptors release]; 
 
 return fetchedResultsController; 
} 
 

加载fetchedResultsController时，我的应用程序崩溃时出现未处理的异常：

  ***由于未捕获异常NSInvalidArgumentException终止应用程序，原因：'实体中未找到keypath objectID< NSSQLEntity Document id = 1> ;'
  

这是我的理解，所有NSManagedObjects有一个objectID，无论是临时还是永久。这不是这样吗？任何想法？

解决方案

更改您的谓词以阅读

  [NSPredicate predicateWithFormat：@self！=％@，[self currentDoc]] 
  


$ b b

其中 currentDoc 是对代表当前文档的 NSManagedObject 实例的引用。

核心数据将在内部进行相等性检查。

I'm using NSFetchedResultsController with a predicate to load a list of Documents in my application. I want to load all the Documents except the currently active one.

I am using Rentzsch's MOGenerator to create a _Document class and then I put all my custom code in the Document subclass. _Document generates an objectID property with type DocumentID.

In the class that creates the controller, I set the controller's currentDocID property:

controller.currentDocID = self.document.objectID;

In the controller itself, I lazy load the fetchedResultsController like this:

- (NSFetchedResultsController *)fetchedResultsController {
    if (fetchedResultsController != nil) {
        return fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Document" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(objectID != %@)", self.currentDocID];
    [fetchRequest setPredicate:predicate];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"dateModified" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    [aFetchedResultsController release];
    [sortDescriptor release];
    [sortDescriptors release];

    return fetchedResultsController;
}

When the fetchedResultsController loads, my app crashes with an unhandled exception:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath objectID not found in entity <NSSQLEntity Document id=1>'

It's my understanding that all NSManagedObjects have an objectID, whether temporary or permanent. Is this not the case? Any thoughts?

解决方案

Change your predicate to read

[NSPredicate predicateWithFormat:@"self != %@", [self currentDoc]]

Where currentDoc is a reference to the instance of the NSManagedObject that represents the current document.

Core Data will do the equality check internally.

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