blocks|key|728723|text|我相信循环遍历返回的数组并调用[NSManagedObjectContext+deleteObject:]是“正确的”/idiomatic方法。这看起来似乎很低效，但请记住，fetch命令实际上并不获取对象的数据，而deleteObject:方法只是将对象标记为删除，在发送[NSManagedObjectContext+save:]时会应用该方法。由于不知道核心数据的内部结构，我不能告诉你它是否像DELETE+WHERE查询一样高效(大概核心数据在内存中有来自fetch的索引主键，并使用这些主键)，但根据我分析核心数据应用程序的经验，它并不比保存新的或更新的对象慢很多。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|728724|entityMap^0|F|12|30|D|3T|U|5K|C|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|G|$]]

I believe looping over the returned array and calling <code>[NSManagedObjectContext deleteObject:]</code> is the "correct"/idiomatic way to do it. It might seem inefficient, but remember that the fetch command doesn't actually fetch the objects' data, and the <code>deleteObject:</code> method just marks the object for deletion, which gets applied when you send <code>[NSManagedObjectContext save:]</code>. Not knowing the internals of Core Data I can't tell you whether it's as efficient as a <code>DELETE WHERE</code> query (presumably Core Data has the indexed primary keys in memory from the fetch, and uses those) but in my experience with profiling Core Data apps it's not significantly slower than saving new or updated objects.

blocks|key|512276|text|NSFetchRequest+*fetchRequest+=+[[NSFetchRequest+alloc]+init];
[fetchRequest+setEntity:[NSEntityDescription+entityForName:TASK_ENTITY+inManagedObjectContext:managedObjectContext];

[fetchRequest+setPredicate:[NSPredicate+predicateWithFormat:@"label+LIKE%25@",+label.text]];

NSError*+error+=+nil;

NSArray*+results+=+[managedObjectContext+executeFetchRequest:fetchRequest+error:&error];

if(![results+count]==0)
{
+++[managedObjectContext+deleteObject:[results+objectAtIndex:0]];
}
if+(![managedObjectContext+save:&error])+{
++++NSLog(@"Whoops,+couldn't+save:+%25@",+[error+localizedDescription]);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|512277|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:TASK_ENTITY inManagedObjectContext:managedObjectContext];

[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@&quot;label LIKE%@&quot;, label.text]];

NSError* error = nil;

NSArray* results = [managedObjectContext executeFetchRequest:fetchRequest error:&amp;error];

if(![results count]==0)
{
 [managedObjectContext deleteObject:[results objectAtIndex:0]];
}
if (![managedObjectContext save:&amp;error]) {
 NSLog(@&quot;Whoops, couldn't save: %@&quot;, [error localizedDescription]);
}
</code></pre>

blocks|key|512333|text|我刚刚尝试了一下，它是成功的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|512334|NSError+*error+=+nil;
NSFetchRequest*+fetchrequest+=+[NSFetchRequest+fetchRequestWithEntityName:@"EntityName"];
[request+setPredicate:[NSPredicate+predicateWithFormat:@"attribute+==+%25@",+variable]];
NSArray+*deleteArray+=+[context+executeFetchRequest:fetchrequest+error:&error];

if+(deleteArray+!=+nil)
{
++++for+(NSManagedObject*+object+in+deleteArray)
++++{
++++++++[context+deleteObject:object];

++++++++//Reload/refresh+table+or+whatever+view..
++++}

++++[context+save:&error];
}|code-block|syntax|javascript|512335|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I just tried this and it is successful:

<pre><code>NSError *error = nil;
NSFetchRequest* fetchrequest = [NSFetchRequest fetchRequestWithEntityName:@"EntityName"];
[request setPredicate:[NSPredicate predicateWithFormat:@"attribute == %@", variable]];
NSArray *deleteArray = [context executeFetchRequest:fetchrequest error:&amp;error];

if (deleteArray != nil)
{
 for (NSManagedObject* object in deleteArray)
 {
 [context deleteObject:object];

 //Reload/refresh table or whatever view..
 }

 [context save:&amp;error];
}
</code></pre>

I know how to use NSPredicate to perform a SQL <code>SELECT</code>-like operation. How can I perform something like <code>DELETE WHERE</code>? Do I have to call <code>[NSManagedObjectContext deleteObject]</code> for each fetched object? Thanks

<pre><code>NSError *error;

NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:TASK_ENTITY inManagedObjectContext:managedObjectContext]];

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"label LIKE %@", label];
[request setPredicate:predicate];

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

[managedObjectContext deleteObject:[array objectAtIndex:0]];
</code></pre>

Core Data: DELETE WHERE

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我知道如何使用NSPredicate来执行SQL SELECT-like操作。我怎样才能执行像DELETE WHERE这样的东西？我必须为每个获取的对象调用[NSManagedObjectContext deleteObject]吗？谢谢NSError *error;NSFetchRequest *request = ...

问核心数据:删除WHERE
EN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问核心数据:删除WHEREEN

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问核心数据:删除WHERE
EN