Core data NSFetchRequest的意外行为

我在上下文中创建了几个实体，以便使用

AppCalendarEntity *appCalendar = [AppCalendarEntity getInstanceWithManagedDocument:manageDocument];

添加几个实体后，我执行流式提取请求

 NSFetchRequest *requestToSeeIfCalendarWithIdExist = [NSFetchRequest fetchRequestWithEntityName:@"AppCalendarEntity"];
   NSArray *result = [managedDocument.managedObjectContext executeFetchRequest:requestToSeeIfCalendarWithIdExist error:&InternalError] ;

它返回的结果仅包括我使用第一个命令在上下文中添加的实体，而不包括已保存在数据库中的条目。我已确保在此阶段文档状态为UIDocumentStateNormal

当我将此行添加到已打开的文档（UIDocumentStateNormal）中时，它会返回预期结果，即从数据库中获取结果以及尚未保存到数据库中的内存上下文

[managedDocument openWithCompletionHandler:^(BOOL success) 
     {
       NSFetchRequest *requestToSeeIfCalendarWithIdExist = [NSFetchRequest fetchRequestWithEntityName:@"AppCalendarEntity"];
   NSArray *result = [managedDocument.managedObjectContext executeFetchRequest:requestToSeeIfCalendarWithIdExist error:&InternalError] ;
}

我的问题是 1-我希望两种情况下的查询结果应该是相同的。为什么在上述情况下并非如此。 2-对我来说，如果文档状态为UIDocumentStateNormal，我不应该在上下文中调用“openWithCompletionHandler”来打开文档。在这个特定的场景中，添加此项后，NSFetchRequest会给我提供所需的结果，这与NSFetchRequest有什么不同

如果我错了，请告诉我

这是完整的代码

这是函数的完整代码

    + (void ) saveCalendarArrayInDbIfItAlreadyDoesNotExist : (NSArray*) appCalendarArray   managedDocument: (UIManagedDocument*) managedDocument completionBlock : ( void(^) (NSArray* ObjectSavedSuccesfully, NSError *InternalError)) handler
        {

        // i dont know why i have to do it :( if i dont add openWithCompletionHandler my query doesnt fetch result from db rather just do query in-memory context and not db
        [managedDocument openWithCompletionHandler:^(BOOL success) 
         {
            void (^completionHandler)(NSArray* , NSError* );
            completionHandler = [handler copy ];

            NSError *error = nil;
            NSMutableArray *array = [[NSMutableArray alloc] init];

            for (id appCalendar in appCalendarArray) {

                if([appCalendar isKindOfClass:[AppCalendarEntity class]])
                {
                    AppCalendarEntity *appCalendarEntity = (AppCalendarEntity*) appCalendar;
                    NSFetchRequest *requestToSeeIfCalendarWithIdExist = [NSFetchRequest fetchRequestWithEntityName:@"MyEntity"];
                    requestToSeeIfCalendarWithIdExist.predicate = [NSPredicate predicateWithFormat:@"identifier = %@", appCalendarEntity.identifier];
                    NSError *InternalError = nil; 
                   [requestToSeeIfCalendarWithIdExist setShouldRefreshRefetchedObjects:YES];
                    NSArray *result = [managedDocument.managedObjectContext executeFetchRequest:requestToSeeIfCalendarWithIdExist error:&InternalError] ;

                   // "result" is different when we encapsulate it in openWithCompletionHandler and when we don't…….MY PROBLEM

                   if(result == nil)
                    {

                         // return error
                    }

                    // 1 object always return that depict the in memory(context) object we created but not saved. I expect it should be zero because no object has yet been saved to database.. 
                    else if(result.count > 1)
                    {

                        [managedDocument.managedObjectContext deleteObject:appCalendar];
                    }
                    else
                    {
                        [array addObject:appCalendarEntity];
                    }
                }
                else
                {

                   // error handling
                }
            }

            if (error != nil)
            {
                 completionHandler (nil, error);
                 return;
            }

            // saving all the objects
             [ managedDocument updateChangeCount:UIDocumentChangeDone ];

    }

---

使用UIManagedDocument时，不要在MOC上调用save，因为它实现了自动保存。但是，需要告知的是，自动保存应该在将来的某个时候进行

去掉该函数中对openWithCompletionHandler的调用（我知道它只是为了调试这个问题）

替换

[managedDocument.managedObjectContext保存：&内部错误]

与

这将通知文档现在可以保存它

编辑

首先，我认为你应该摆脱调试黑客。您可以添加NSLog或NSAssert，但其他这些东西只会让您很难说出为什么要添加，并混淆了真正的问题

第二，你在这里的真正目标是什么？我可以看到方法的名称，也可以看到代码，但它们不匹配

这里有太多的“积垢”，很难理解你的问题。我将重新发布您的代码，同时进行编辑以删除“打开的”内容，并用问题作为代码注释对其进行注释

希望这个改变能帮助你解决问题

// First, the method name seems to indicate that some objects will be added
// to the database.  however, the only database work in this method is removal.
// I don't get it.
+ (void ) saveCalendarArrayInDbIfItAlreadyDoesNotExist : (NSArray*) appCalendarArray   managedDocument: (UIManagedDocument*) managedDocument
    {
        NSError *error = nil;
        NSMutableArray *array = [[NSMutableArray alloc] init];

        for (id appCalendar in appCalendarArray) {
            if([appCalendar isKindOfClass:[AppCalendarEntity class]]) {
                // OK, we are filtering the array of objects.  We are only interested in
                // objects of type AppCalendarEntity, and are going to use its identity
                // property to look for objects of type MyEntity.
                // What is the relationship between AppCalendarEntity and MyEntity?
                AppCalendarEntity *appCalendarEntity = (AppCalendarEntity*) appCalendar;
                NSFetchRequest *requestToSeeIfCalendarWithIdExist = [NSFetchRequest fetchRequestWithEntityName:@"MyEntity"];
                requestToSeeIfCalendarWithIdExist.predicate = [NSPredicate predicateWithFormat:@"identifier = %@", appCalendarEntity.identifier];
                NSError *InternalError = nil; 
               [requestToSeeIfCalendarWithIdExist setShouldRefreshRefetchedObjects:YES];
                NSArray *result = [managedDocument.managedObjectContext executeFetchRequest:requestToSeeIfCalendarWithIdExist error:&InternalError];

               // OK, now we just got a result from searching for a MyEntity, where
               // its identifier is the same as the appCalendarEntity.
               if(result == nil)
               {
                   // return error
               }
                // 1 object always return that depict the in memory(context) object we created but not saved. I expect it should be zero because no object has yet been saved to database.. 
                else if(result.count > 1)
                {
                    // I am extremely confused by this code.  First, why are you
                    // checking for more than 1 object?  The method name indicates
                    // you are going to insert something.  Furthermore, you are only
                    // deleting one object.  How many do you expect?  Also, why are
                    // you deleting an appCalendar?  You were searching for a MyEntity.
                    // If an appCalendar is a MyEntity, then that's terrible naming.
                    // Furthermore, it would explain why you are finding it...
                    // because you create entities by inserting them in a MOC to
                    // begin with!
                    [managedDocument.managedObjectContext deleteObject:appCalendar];
                }
                else
                {
                    // Even more confusion.  You are adding this object to an internal
                    // array, not the database.  Furthermore, you are doing it if there
                    // are either 0 or 1 MyEntity objects in the database with matching
                    // identifier.
                    [array addObject:appCalendarEntity];
                }
            }
        }

        // saving all the objects
        // OK - but the only thing being saved are the ones you deleted...
        [ managedDocument updateChangeCount:UIDocumentChangeDone ];
}

最后，如果我的直觉是正确的，日历对象实际上是MyEntity对象，它们已经在MOC中了——因为它们就是这样创建的。在执行提取时，可以强制搜索忽略挂起的更改（如我前面的一条评论中所述），而只接受保存的更改

如果要忽略挂起的更改

fetchRequest.includesPendingChanges = NO;

---

使用UIManagedDocument时，不要在MOC上调用save，因为它实现了自动保存。但是，需要告知的是，自动保存应该在将来的某个时候进行

去掉该函数中对openWithCompletionHandler的调用（我知道它只是为了调试这个问题）

替换

[managedDocument.managedObjectContext保存：&内部错误]

与

这将通知文档现在可以保存它

编辑

首先，我认为你应该摆脱调试黑客。您可以添加NSLog或NSAssert，但其他这些东西只会让您很难说出为什么要添加，并混淆了真正的问题

第二，你在这里的真正目标是什么？我可以看到方法的名称，也可以看到代码，但它们不匹配

这里有太多的“积垢”，很难理解你的问题。我将重新发布您的代码，同时进行编辑以删除“打开的”内容，并用问题作为代码注释对其进行注释

希望这个改变能帮助你解决问题

// First, the method name seems to indicate that some objects will be added
// to the database.  however, the only database work in this method is removal.
// I don't get it.
+ (void ) saveCalendarArrayInDbIfItAlreadyDoesNotExist : (NSArray*) appCalendarArray   managedDocument: (UIManagedDocument*) managedDocument
    {
        NSError *error = nil;
        NSMutableArray *array = [[NSMutableArray alloc] init];

        for (id appCalendar in appCalendarArray) {
            if([appCalendar isKindOfClass:[AppCalendarEntity class]]) {
                // OK, we are filtering the array of objects.  We are only interested in
                // objects of type AppCalendarEntity, and are going to use its identity
                // property to look for objects of type MyEntity.
                // What is the relationship between AppCalendarEntity and MyEntity?
                AppCalendarEntity *appCalendarEntity = (AppCalendarEntity*) appCalendar;
                NSFetchRequest *requestToSeeIfCalendarWithIdExist = [NSFetchRequest fetchRequestWithEntityName:@"MyEntity"];
                requestToSeeIfCalendarWithIdExist.predicate = [NSPredicate predicateWithFormat:@"identifier = %@", appCalendarEntity.identifier];
                NSError *InternalError = nil; 
               [requestToSeeIfCalendarWithIdExist setShouldRefreshRefetchedObjects:YES];
                NSArray *result = [managedDocument.managedObjectContext executeFetchRequest:requestToSeeIfCalendarWithIdExist error:&InternalError];

               // OK, now we just got a result from searching for a MyEntity, where
               // its identifier is the same as the appCalendarEntity.
               if(result == nil)
               {
                   // return error
               }
                // 1 object always return that depict the in memory(context) object we created but not saved. I expect it should be zero because no object has yet been saved to database.. 
                else if(result.count > 1)
                {
                    // I am extremely confused by this code.  First, why are you
                    // checking for more than 1 object?  The method name indicates
                    // you are going to insert something.  Furthermore, you are only
                    // deleting one object.  How many do you expect?  Also, why are
                    // you deleting an appCalendar?  You were searching for a MyEntity.
                    // If an appCalendar is a MyEntity, then that's terrible naming.
                    // Furthermore, it would explain why you are finding it...
                    // because you create entities by inserting them in a MOC to
                    // begin with!
                    [managedDocument.managedObjectContext deleteObject:appCalendar];
                }
                else
                {
                    // Even more confusion.  You are adding this object to an internal
                    // array, not the database.  Furthermore, you are doing it if there
                    // are either 0 or 1 MyEntity objects in the database with matching
                    // identifier.
                    [array addObject:appCalendarEntity];
                }
            }
        }

        // saving all the objects
        // OK - but the only thing being saved are the ones you deleted...
        [ managedDocument updateChangeCount:UIDocumentChangeDone ];
}

最后，如果我的直觉是正确的，日历对象实际上是MyEntity对象，它们已经在MOC中了——因为它们就是这样创建的。在执行提取时，可以强制搜索忽略挂起的更改（如我前面的一条评论中所述），而只接受保存的更改

如果要忽略挂起的更改

fetchRequest.includesPendingChanges = NO;

---

@Jody的问题已经解决了，感谢您抽出时间回答这个问题

AppCalendarEntity *appCalendar = [AppCalendarEntity getInstanceWithManagedDocument:manageDocument];

首先让我谈谈你的困惑

1-是功能旨在保存在数据库中，它是一个帮助功能。传递给此函数的参数“appCalendarArray”由已在上下文中创建的实体组成。我故意消除了逻辑，因为它涉及与外部API通信、解析json等。在上下文中插入实体所需的代码已经包含在问题的第一部分中

AppCalendarEntity *appCalendar = [AppCalendarEntity getInstanceWithManagedDocument:manageDocument];

2-我根据数据库中应该是唯一的列，从上下文中删除已构建但尚未从上下文中保存的实体。若数据库中已有对象的标识符，则不希望重新保存它。所以，我只是从上下文中删除它。此函数按预期工作，实体不会重新保存在数据库中。最后一行不保存保留在上下文中的对象（如果有）。大多数时候都有很多

3-很抱歉输入错误AppCalendarEntity和MyEntity是相同的

解决方案

---

---

我已添加此标志fetchRequest.includesPendingChanges=NO，删除数据库，重新启动Xcode，它开始工作。感谢您的坚持

@Jody问题已经解决，感谢您抽出时间回答这个问题

AppCalendarEntity *appCalendar = [AppCalendarEntity getInstanceWithManagedDocument:manageDocument];

首先让我谈谈你的困惑

1-是功能旨在保存在数据库中，它是一个帮助功能。传递给此函数的参数“appCalendarArray”由已在上下文中创建的实体组成。我故意消除了逻辑，因为它涉及与外部API通信、解析json等。在上下文中插入实体所需的代码已经包含在问题的第一部分中

AppCalendarEntity *appCalendar = [AppCalendarEntity getInstanceWithManagedDocument:manageDocument];

2-我从contex中删除实体