我们如何检索在 iOS 中使用核心数据保存的数据

Posted 2023-03-05

【中文标题】我们如何检索在 iOS 中使用核心数据保存的数据

【英文标题】：How do we Retrive Data Which is Saved By Using Core Data in iOS

【发布时间】：2014-01-03 10:38:09

【问题描述】：

我是 Core Data 的新手。我已经开发了一个应用程序。在我的应用程序中，我有注册、登录、忘记密码表格。

在注册表中我写这个代码来注册。

NSEntityDescription *entitydesc = [NSEntityDescription entityForName:@"User" inManagedObjectContext:context];
NSManagedObject *newuser = [[NSManagedObject alloc]initWithEntity:entitydesc insertIntoManagedObjectContext:context];

[newuser setValue:self.registerUsername.text forKey:@"username"];
[newuser setValue:self.registerPassword.text forKey:@"password"];
[newuser setValue:self.registerConfirmPassword.text forKey:@"confirmpassword"];
[newuser setValue:self.registerMobileNumber.text forKey:@"mobilenumber"];

NSError *error;
[context save:&error];  

在登录表单中我写了这段代码：

NSEntityDescription *entitydesc = [NSEntityDescription entityForName:@"User" inManagedObjectContext:context];

NSFetchRequest *request = [[NSFetchRequest alloc]init];
    [request setEntity:entitydesc];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"username like %@ and password like %@",self.logUsername.text,self.logPassword.text];
    [request setPredicate:predicate];

    NSError *error;
    NSArray *matchingData = [context executeFetchRequest:request error:&error];
    if(matchingData.count<=0)
    
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Error!" message:@"Username and password does not match" delegate:self cancelButtonTitle:@"OK" otherButtonTitles: nil];
        [alert show];

    
    else
    
        NSString *username;
        NSString *password;
        for(NSManagedObject *obj in matchingData)
        
            username = [obj valueForKey:@"username"];
            password = [obj valueForKey:@"password"];
        
        SecurityHome *securityhome = [[SecurityHome alloc]init];
        [self.navigationController pushViewController:securityhome animated:YES];
    

两者都工作正常。如果用户输入的用户名和手机号码正确，我现在想在忘记密码页面显示密码。我怎样才能做到这一点？

【问题讨论】：

希望永远不会。您最好存储加密的密码，如果用户忘记了他的密码，您可以向他发送一个新密码。但我不会使用将我的纯密码存储在数据库中的应用程序......

我支持 Dehlen。你真的不应该这样做。无论如何，您可能需要此信息用于其他目的，所以我已经回答了您的问题

【参考方案1】：

设置示例谓词和排序顺序...

NSNumber *minimumSalary = ...;
NSPredicate *predicate = [NSPredicate predicateWithFormat:
@"(lastName LIKE[c] 'Worsley') AND (salary > %@)", minimumSalary];
[request setPredicate:predicate];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]
initWithKey:@"firstName" ascending:YES];
[request setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
[sortDescriptor release];

NSError *error = nil;
NSArray *array = [moc executeFetchRequest:request error:&error];
if (array == nil)

    // Deal with error...

【参考方案2】：

在问这个问题之前，您应该先进行一些“谷歌搜索”。无论如何，让我为你做。给你。Core Data NSFetchResult guide for developer Ray wenderlich- Really nice tutorial

在列出的两个链接中，我都在尝试推荐 NSFetchResultControllers，因为它们既快速又简单。在这里你可以看到不同之处 没有 NSFetchResultController， NSManagedObjectContext *moc = [self managedObjectContext]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:moc]; NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease]; [请求 setEntity:entityDescription];

// Set example predicate and sort orderings...
NSNumber *minimumSalary = ...;
NSPredicate *predicate = [NSPredicate predicateWithFormat:
    @"(lastName LIKE[c] 'Worsley') AND (salary > %@)", minimumSalary];
[request setPredicate:predicate];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]
    initWithKey:@"firstName" ascending:YES];
[request setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
[sortDescriptor release];

NSError *error = nil;
NSArray *array = [moc executeFetchRequest:request error:&error];
if (array == nil)

    // Deal with error...

使用 NSFetchresultController

[[self managedObjectContext] fetchObjectsForEntityName:@"Employee" withPredicate:
    @"(lastName LIKE[c] 'Worsley') AND (salary > %@)", minimumSalary];

这些示例适用于 Famous 员工表。根据您的要求翻译代码。如果您因任何原因无法使用此代码，请告诉我..

【参考方案3】：

You can use this code for fetching details and pass the object to Forgot class and show there.


-(User*)getUserCredentialDetails:(NSUInteger)mobilenumber


    NSError *error = nil;

    NSFetchRequest *request = [[NSFetchRequest alloc] init];

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"User" inManagedObjectContext:managedObjectContext];

    [request setEntity:entity];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"mobilenumber = %d",mobileNumber];

    [request setPredicate:predicate];

    NSArray * resultArray = [managedObjectContext executeFetchRequest:request error:&error];

    [request release];

    if (error != nil)
      

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

      

    return [resultArray lastObject];