Question

我最近开始处理Core Data，在我的测试中，我发现大约有20％的时间数据实际保存到数据库中。剩下的时间，它只是临时保存，而应用程序正在运行。如果我重新启动，我保存的最后一个数据会丢失。

有谁知道问题可能是什么？

以下是代码：

//Save data
NSEntityDescription *users = [NSEntityDescription insertNewObjectForEntityForName:@"Users" inManagedObjectContext:document.managedObjectContext];
[users setValue:@"Name Test" forKey:@"name"];
[users setValue:[NSNumber numberWithInt:20] forKey:@"age"];
[users setValue:@"Some Country" forKey:@"location"];


//Debugging
//no error ever shows up
NSError *error;
if(![document.managedObjectContext save:&error]) {
    NSLog(@"Error: %@", error);
}

//this is just to show that the problem may not be with my UIManagedDocument (self.document), since the NSLog never gets called.
if(self.document.documentState != UIDocumentStateNormal) {
    NSLog(@"Document is not opened");
}
//End of debugging


//Fetch all the data from the entity
NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Users"];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
fetch.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

NSArray *results = [document.managedObjectContext executeFetchRequest:fetch error:nil];
NSLog(@"Results on the database: %d", [results count]);

document是同一件事（至少在大多数情况下我希望如此）self.document;它只是该代码所在方法的一个参数。

这是我的.h和.m的代码：

·H

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>

@interface CoreDataViewController : UIViewController

@property (nonatomic, strong) UIManagedDocument *document;

@end

的.m：

#import "CoreDataViewController.h"

@implementation CoreDataViewController
@synthesize document = _document;

- (void)fetchStuff:(UIManagedDocument *)document {

    //Save data
    NSEntityDescription *users = [NSEntityDescription insertNewObjectForEntityForName:@"Users" inManagedObjectContext:document.managedObjectContext];
    [users setValue:@"Name Test" forKey:@"name"];
    [users setValue:[NSNumber numberWithInt:20] forKey:@"age"];
    [users setValue:@"Some Country" forKey:@"location"];


    //Debugging
    //no error ever shows up
    NSError *error;
    if(![document.managedObjectContext save:&error]) {
        NSLog(@"Error: %@", error);
    }

    //this is just to show that the problem may not be with my UIManagedDocument (self.document), since the NSLog never gets called.
    if(document.documentState != UIDocumentStateNormal) {
        NSLog(@"Document is not opened");
    }
    //End of debugging


    //Fetch all the data from the entity
    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Users"];
    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
    fetch.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

    NSArray *results = [document.managedObjectContext executeFetchRequest:fetch error:nil];
    NSLog(@"Results on the database: %d", [results count]);
}

- (void)useDocument {
    if(![[NSFileManager defaultManager] fileExistsAtPath:[self.document.fileURL path]]) {
        [self.document saveToURL:self.document.fileURL forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success){
            if(success == YES) NSLog(@"created");
            [self fetchStuff:self.document];
        }];
    } else if(self.document.documentState == UIDocumentStateClosed) {
        [self.document openWithCompletionHandler:^(BOOL success) {
            if(success == YES) NSLog(@"opened");
            [self fetchStuff:self.document];
        }];
    } else if(self.document.documentState == UIDocumentStateNormal) {
        [self fetchStuff:self.document];
    }
}

- (void)setDocument:(UIManagedDocument *)document {
    if(_document != document) {
        _document = document;
        [self useDocument];
    }
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    if(!self.document) {
        NSURL *url = [[[NSFileManager defaultManager]URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
        url = [url URLByAppendingPathComponent:@"Database"];
        self.document = [[UIManagedDocument alloc]initWithFileURL:url];
    }
}

@end

注意：还有我的数据模型，它有一个名为“Users”的实体，其属性为age，location，name。

Answer 1

有时因为自动保存而保存数据，每次X（可能是10，我需要检查文档）秒发生。为了强制保存，我应该使用它：

[documentation saveToURL:documentation.fileURL forSaveOperation:UIDocumentSaveForOverwriting completionHandler:^(BOOL success) {
if(success == YES) NSLog(@"Awesome, it's saved!");
}];

虽然将此代码添加到fetchStuff中可以正常工作，但最好在用户退出屏幕时实现此功能，因为它可以通过自动保存自动保存。

Answer 2

您不应该在UIManagedDocument MOC上调用save。这是您的代码的编辑版本。请试一试。

//Save data
NSEntityDescription *users = [NSEntityDescription insertNewObjectForEntityForName:@"Users" inManagedObjectContext:document.managedObjectContext];
[users setValue:@"Name Test" forKey:@"name"];
[users setValue:[NSNumber numberWithInt:20] forKey:@"age"];
[users setValue:@"Some Country" forKey:@"location"];

// Removed save on UIMDMOC - We let auto-save do the work
// However, we have to tell the document that it needs to 
// be saved. Now, the changes in the "main" MOC will get pushed
// to the "parent" MOC, and when appropriate, will get save to disk.
[document updateChangeCount:UIDocumentChangeDone];

if(self.document.documentState != UIDocumentStateNormal) {
    NSLog(@"Document is not opened");
}    

//Fetch all the data from the entity
NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Users"];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
fetch.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

NSArray *results = [document.managedObjectContext executeFetchRequest:fetch error:nil];
NSLog(@"Results on the database: %d", [results count]);

好的......这不是太痛苦...只是删除了保存的调用，并用一个告诉UIManagedDocument的调用替换了它已经进行了一些更改，并且需要保存。

Answer 3

    Record *newentry = [NSEntityDescription insertNewObjectForEntityForName:@"Record" inManagedObjectContext:self.mManagedObjectContext];
    newentry.code = entryStr;
    NSError *error;
    if ([self.mManagedObjectContext save:&error])
    {
        NSLog(@"save successfully");
    }
    else
    {
        NSLog(@"fail to save");
    }

应用程序关闭80％的时间后，保存的核心数据不会保留

3 个答案: