使用核心数据将数据存储到 sqlite 表的问题

Posted 2023-03-04

【中文标题】使用核心数据将数据存储到 sqlite 表的问题

【英文标题】：problem storing data to sqlite table using core data

【发布时间】：2011-06-25 03:51:12

【问题描述】：

    IfIDieAppDelegate.m

   - (void)createEditableCopyOfDatabaseIfNeeded

     

    // First, test for existence. 
    BOOL success; 

    NSFileManager *fileManager = [NSFileManager defaultManager]; 

    NSError *error; 

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 

    NSString *documentsDirectory = [paths objectAtIndex:0]; 

    //NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"DeathDiary.sqlite"];

    NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"IfIDie.sqlite"];

    NSLog(@"%@",writableDBPath);

    success = [fileManager fileExistsAtPath:writableDBPath]; 

    if (success==YES)

    

        NSLog(@"Database Already Exists");
        return;
    
    else 

        NSLog(@"New Database Created");

        // The writable database does not exist, so copy the default to the appropriate location. 


    NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"IfIDie.sqlite"]; 

        NSLog(@"Default : %@",defaultDBPath);

        success = [fileManager copyItemAtPath:defaultDBPath toPath:writableDBPath error:&error]; 

        if (!success)  

            NSAssert1(0, @"Failed to create writable database file with message '%@'.", [error localizedDescription]); 

         

    




- (NSPersistentStoreCoordinator *)persistentStoreCoordinator 

    if (persistentStoreCoordinator != nil) 

        return persistentStoreCoordinator;

    

    NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"IfIDie.sqlite"]];

    NSError *error = nil;

    persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];

    if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:nil error:&error]) 


        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
        

    return persistentStoreCoordinator;



NoteEditController.m


- (void)viewWillDisappear:(BOOL)animated

    [super viewWillDisappear:animated];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardDidShowNotification object:nil];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];

    if(saveChanges)

        // Save any changes to note
        if([[noteTextView text] length] > 0)

            if(noteToEdit)

                // Edit Note
                if([[titleField text] length] <= 0)

                    [noteToEdit setNoteTitle:[noteTextView text]];

                else

                    [noteToEdit setNoteTitle:[titleField text]];

                [noteToEdit setNoteText:[noteTextView text]];

             else 
                // New Note
                Note *newNote = [NSEntityDescription 
insertNewObjectForEntityForName:@"Note" inManagedObjectContext:context];

                if([[titleField text] length] <= 0)

                    [newNote setNoteTitle:[noteTextView text]];

                else

                    [newNote setNoteTitle:[titleField text]];


                [newNote setNoteText:[noteTextView text]];

                NSLog(@"data saved");


            

         else 
            // Remove note (zero length)

            if(noteToEdit)

                [context deleteObject:noteToEdit];
            
        
    

这里似乎一切正常，但数据仍然没有保存到表中。可能有什么问题？ 数据库重新加载有什么问题吗？如果，那么我不知道如何解决。 没有错误。它显示已保存但未保存到表的数据的 nslog。

【问题讨论】：

请编辑您的帖子以删除行间多余的空格，并正确指定代码块（代码突出显示时的花括号按钮“”）。像现在这样，它是不可读的

【参考方案1】：

您需要在viewWillDisappear: 方法的末尾保存上下文以实际提交您的更改

NSError *error = nil; 
if (![context save: &error]) 
    // Couldn't save

【讨论】：

它完成了。但很抱歉，我不知道这段代码是如何提交插入的。你能解释一下吗？

context 是文档中提到的便签本。您的所有更改（插入、删除和编辑）都存储在上下文中，并且只有在您调用 save: 时才会写入数据库。如果你不这样做，数据库就不会改变。