从另一个方法从NSManagedObjectContext中删除对象 [英] Delete objects from NSManagedObjectContext from another method

问题描述

我想删除所有的对象，但我似乎无法使它的工作。我知道这种问题还有其他问题，但他们没有帮助。我想要的是在这个方法中删除section和fixture实体中的所有对象。

   - （void）refresh：（UIRefreshControl *）refreshControl {
 [refreshControl endRefreshing]; 
} 
  

这是我在另一个方法中保存和获取对象的地方。

  NSManagedObjectContext * context = [self managedObjectContext]; 
 
 for（int i = 0; i <= fixtures.count-1; i ++）{
 
 fixture = [NSEntityDescription insertNewObjectForEntityForName：@FixtureinManagedObjectContext：context] ; 
 
 [fixture setValue：[NSString stringWithFormat：@％@，[[fixtures objectAtIndex：i] objectForKey：@date]] forKey：@date]; 
 [fixture setValue：[[fixtures objectAtIndex：i] objectForKey：@time] forKey：@time]; 
 [fixture setValue：[[fixtures objectAtIndex：i] objectForKey：@home] forKey：@home]; 
 [fixture setValue：[[fixtures objectAtIndex：i] objectForKey：@away] forKey：@away]; 
 [fixture setValue：[[fixtures objectAtIndex：i] objectForKey：@league] forKey：@league]; 
} 
 
 for（int i = 0; i <= sections.count-1; i ++）{
 lolSection = [NSEntityDescription insertNewObjectForEntityForName：@SectioninManagedObjectContext：context ]; 
 [lolSection setValue：[NSString stringWithFormat：@％@，[[section objectAtIndex：i] objectForKey：@date]] forKey：@date]; 
} 
 
 NSManagedObjectContext * managedObjectContext = [self managedObjectContext]; 
 NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] initWithEntityName：@Fixture]; 
 self.theFixtures = [[managedObjectContext executeFetchRequest：fetchRequest error：nil] mutableCopy]; 
 
 NSFetchRequest * fetchRequest2 = [[NSFetchRequest alloc] initWithEntityName：@Section]; 
 self.theSection = [[managedObjectContext executeFetchRequest：fetchRequest2 error：nil] mutableCopy]; 
 
 NSSortDescriptor * descriptor = [[NSSortDescriptor alloc] initWithKey：@selfascending：NO]; 
 NSArray * descriptors = [NSArray arrayWithObject：descriptor]; 
 NSArray * reverseTheArray = [[self.theSection valueForKey：@date] sortedArrayUsingDescriptors：descriptors]; 
 reversedArray = [[reverseTheArray reverseObjectEnumerator] allObjects]; 
  

解决方案

p>

根据文档。

删除托管对象很简单。您只需发送
管理对象上下文a deleteObject：消息，传递您
要删除的对象作为参数。

换句话说，使用有效的上下文表示

  [aValidContext deleteObject：managedObjectYouWantToDelete]; 
  

关于您的问题，您需要

1. 设置抓取请求以抓取 Fixture 项目


2. 循环结果c> NSArray ）并执行删除

例如

  NSFetchRequest * request = //在这里创建请求... 
 
 NSError * error; 
 NSArray * array = [aValidContext executeFetchRequest：request error：& error]; 
 if（array == nil）{
 //处理错误... 
} else {
 //循环数组执行deleteObject 
} 
 
 //保存到持久存储
  

剩下的代码留待练习;）

编辑1

再次阅读您的问题， Section 和 Fixture ？如果它们是分开的实体，您还应为节执行以前的步骤。

I'm trying to delete all the objects, but I can't seem to make it work. I know there is other questions for this kind of question, but they are not helpful. What I want is to delete all the objects in section and fixture entity in this method.

- (void)refresh:(UIRefreshControl *)refreshControl {    
    [refreshControl endRefreshing];
}

This is where I save and fetch my objects in another method.

NSManagedObjectContext *context = [self managedObjectContext];

for (int i=0; i <=fixtures.count-1; i++) {

    fixture = [NSEntityDescription insertNewObjectForEntityForName:@"Fixture" inManagedObjectContext:context];

    [fixture setValue:[NSString stringWithFormat:@"%@",[[fixtures objectAtIndex:i] objectForKey:@"date"]] forKey:@"date"];
    [fixture setValue:[[fixtures objectAtIndex:i] objectForKey:@"time"] forKey:@"time"];
    [fixture setValue:[[fixtures objectAtIndex:i] objectForKey:@"home"] forKey:@"home"];
    [fixture setValue:[[fixtures objectAtIndex:i] objectForKey:@"away"] forKey:@"away"];
    [fixture setValue:[[fixtures objectAtIndex:i] objectForKey:@"league"] forKey:@"league"];
}

for (int i=0; i <=sections.count-1; i++) {
    lolSection = [NSEntityDescription insertNewObjectForEntityForName:@"Section" inManagedObjectContext:context];
    [lolSection setValue:[NSString stringWithFormat:@"%@",[[sections objectAtIndex:i] objectForKey:@"date"]] forKey:@"date"];
}

NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Fixture"];
self.theFixtures = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];

NSFetchRequest *fetchRequest2 = [[NSFetchRequest alloc] initWithEntityName:@"Section"];
self.theSection= [[managedObjectContext executeFetchRequest:fetchRequest2 error:nil] mutableCopy];

NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"self" ascending:NO];
NSArray *descriptors = [NSArray arrayWithObject: descriptor];
NSArray* reverseTheArray = [[self.theSection valueForKey:@"date"] sortedArrayUsingDescriptors:descriptors];
reversedArray = [[reverseTheArray reverseObjectEnumerator] allObjects];

解决方案

So, what have you tried so far?

As per the documentation.

Deleting a managed object is straightforward. You simply send its managed object context a deleteObject: message, passing the object you want to delete as the argument.

In other words, using a valid context you shoul say

[aValidContext deleteObject:managedObjectYouWantToDelete];

About your question, you need to

1. Setup a fetch request to grab the Fixture items
2. Loop the results (an NSArray) and perform the deletion

For example

NSFetchRequest* request = // create the request here...

NSError *error;
NSArray *array = [aValidContext executeFetchRequest:request error:&error];
if (array == nil) {
    // Deal with error...
} else {
    // loop the array performing deleteObject
}

// save to persistent store

Remaining code is left for exercise ;)

Edit 1

Reading again your question, what is the relationship between Section and Fixture? If they are separated entities, you should perform previous steps also for Sections.

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