有什么方法可以限制核心数据中的重复条目吗？ [英] Is there any way we can restrict duplicate entries in core data?

问题描述

我一直在尝试在核心数据中添加对象。所以，我想它不应该允许在核心数据存储中的重复条目。怎么做？
这是我的代码与保存数据相关。

   - （IBAction）save： b {
 
 if（[name.text isEqualToString：@]&& [address.text isEqualToString：@]&& [phone.text isEqualToString：@] ）
 {
 
 UIAlertView * alert = [[UIAlertView alloc] initWithTitle：@Yo ..！ 
 message：@Data Not Saved
 delegate：nil 
 cancelButtonTitle：@OK
 otherButtonTitles：nil]; 
 [alert show]; 
} 
 else 
 {
 coreDataAppDelegate * appDelegate = [[UIApplication sharedApplication] delegate]; 
 
 NSManagedObjectContext * context = [appDelegate managedObjectContext]; 
 
 
 NSManagedObject * newContact; 
 newContact = [NSEntityDescription 
 insertNewObjectForEntityForName：@Contacts
 inManagedObjectContext：context]; 
 
 
 [newContact setValue：name.text forKey：@name]; 
 [newContact setValue：address.text forKey：@address]; 
 [newContact setValue：phone.text forKey：@phone]; 
 
 
 name.text = @; 
 address.text = @; 
 phone.text = @; 
 
 NSError * error; 
 [context save：& error]; 
 
 UIAlertView * alert = [[UIAlertView alloc] initWithTitle：@Yo ..！ 
 message：@Data Saved
 delegate：nil 
 cancelButtonTitle：@OK
 otherButtonTitles：nil]; 
 [alert show]; 
 
 NSLog（@Object Saved\\\
）; 
 
} 
 
 
} 
  

解决方案

由于没有可用的内置方法，您需要获取结果，并检查结果是否包含您不想重复的对象。

这里是代码片段：

   - （void）checkForDuplicates 
 {
 NSEntityDescription * entity = [NSEntityDescription entityForName：@Students
 inManagedObjectContext：managedObjectContext]; 
 
 NSFetchRequest * request = [[NSFetchRequest alloc] init]; 
 [request setEntity：entity]; 
 
 NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey：@students
 ascending：NO]; 
 NSArray * sortDescriptors = [NSArray arrayWithObject：sortDescriptor]; 
 
 [request setSortDescriptors：sortDescriptors]; 
 [sortDescriptor release]; 
 
 NSError * Fetcherror; 
 NSMutableArray * mutableFetchResults = [[managedObjectContext 
 executeFetchRequest：request error：& Fetcherror] mutableCopy]; 
 
 if（！mutableFetchResults）{
 //错误处理代码。 
} 
 
 if（[[mutableFetchResults valueForKey：@users] 
 containsObject：name.text]）{
 //通知重复
 return ; 
} 
 else 
 {
 //写您的代码以添加数据
} 
} 
  pre> 
 
 
希望这可以帮助你！
 
I have been trying to add objects in core data. So, i want that it should not allow duplicate entries in core data store. How to do that?
This is my code related to save data.
  -(IBAction)save:(id)sender
    {

        if([name.text isEqualToString:@""] && [address.text isEqualToString:@""] && [phone.text isEqualToString:@""])
        {

            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Yo..!"
                                                        message:@"Data Not Saved"
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
            [alert show];
        }
    else
    {
        coreDataAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

        NSManagedObjectContext *context = [appDelegate managedObjectContext];


        NSManagedObject *newContact;
        newContact = [NSEntityDescription
                      insertNewObjectForEntityForName:@"Contacts"
                      inManagedObjectContext:context];


        [newContact setValue:name.text forKey:@"name"];
        [newContact setValue:address.text forKey:@"address"];
        [newContact setValue:phone.text forKey:@"phone"];


        name.text = @"";
        address.text = @"";
        phone.text = @"";

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

        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Yo..!"
                                                    message:@"Data Saved"
                                                   delegate:nil
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles:nil];
        [alert show];

         NSLog(@"Object Saved\n");

    }


}

解决方案
As there is no built in method available, you need to fetch results and check whether result contains object you don't want to be duplicated.

Here is code snippet:
-(void)checkForDuplicates
{
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Students"
                                          inManagedObjectContext:managedObjectContext];

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

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"students"
                                                               ascending:NO];
    NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

    [request setSortDescriptors:sortDescriptors];
    [sortDescriptor release];

    NSError *Fetcherror;
    NSMutableArray *mutableFetchResults = [[managedObjectContext
                                        executeFetchRequest:request error:&Fetcherror] mutableCopy];

   if (!mutableFetchResults) {
        // error handling code.
    }

    if ([[mutableFetchResults valueForKey:@"users"]
         containsObject:name.text]) {
        //notify duplicates
        return;
    }
    else
    {
         //write your code to add data
    }
}
Hope this may help you!

                        
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