核心数据:查询谓词中的objectID？

Question

我使用获取请求和谓词从Core Data持久性存储中获取一组对象.我当前的谓词只是检查属性是否> =某个值.这一切都很好,除了我想最终排除当前在数组中保存的任何对象.

我基本上需要能够排除一组对象,我认为我能做到这一点的唯一方法是能够objectID从我的托管对象数组中获取一个列表,并在我的谓词中创建另一个表达式以确保任何对象返回不一样objectID.IE @"ANY records.objectID NOT IN %@", arrayOfObjectID.

我怎样才能做到这一点？

Answer 1

像谓词一样

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT (self IN %@)", arrayOfExcludedObjects];

其中获取请求的实体是数组中对象的实体,应该做你想要的.当然,这可以与单个谓词中的其他子句组合用于获取请求.

通常,对象比较(例如self == %@或self IN %@)objectID在核心数据查询中进行比较.该参数可以是一个NSManagedObject实例或一个NSMangedObjectID实例.所以,上面的谓语形式可以采取arrayOfExcludedObjects或者[arrayOfExcludedObjects valueForKey:@"objectID"]作为参数.

Answer 2

虽然@ BarryWark在使用获取请求时的答案是正确的,但我想向那些尝试将此规则应用于过滤Core Data to-many关系的人员发出警告.

简而言之:如果在过滤多个关系时使用谓词而IN查询的对象数组是一个objectIDs数组 - 那么你应该在查询字符串中使用self.objectID

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(self.objectID IN %@)", arrayOfObjectIDs];

因为仅(self IN %@)在过滤到多个关系的情况下使用将导致不正确的结果 - 它只是一个NSArray来评估谓词,它对Core Data的NSManagedObjectID内容一无所知.

我制作了特殊的测试代码来展示这一点.很抱歉这么多线路,但值得.有两个实体:User和Post,User有一个名为"posts"的多对多关系.

User *user = [NSEntityDescription insertNewObjectForEntityForName:NSStringFromClass([User class]) inManagedObjectContext:managedObjectContext()];

Post *post = [NSEntityDescription insertNewObjectForEntityForName:NSStringFromClass([Post class]) inManagedObjectContext:managedObjectContext()];

[user addPostsObject:post];

[managedObjectContext() save:nil];

// 1. Both filtered relationship array and fetch result are correct!
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(self IN %@)", @[ post ]];

NSSet *filteredRelationship = [user.posts filteredSetUsingPredicate:predicate];

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Post"];
NSArray *fetchResult = [managedObjectContext() executeFetchRequest:fetchRequest error:nil];

NSLog(@"\n\n\nPredicate: %@", predicate);
NSLog(@"filteredRelationship: %@", filteredRelationship);
NSLog(@"fetchResult: %@", fetchResult);

// 2. Filtered relationship array is empty (wrong), fetch result is correct, !
predicate = [NSPredicate predicateWithFormat:@"(self IN %@)", @[ post.objectID ]];

filteredRelationship = [user.posts filteredSetUsingPredicate:predicate];

fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Post"];
fetchResult = [managedObjectContext() executeFetchRequest:fetchRequest error:nil];

NSLog(@"\n\n\nPredicate: %@", predicate);
NSLog(@"filteredRelationship: %@", filteredRelationship);
NSLog(@"fetchResult: %@", fetchResult);

// 3. Filtered relationship array is empty (wrong), fetch result is correct
predicate = [NSPredicate predicateWithFormat:@"(self.objectID IN %@)", @[ post ]];

filteredRelationship = [user.posts filteredSetUsingPredicate:predicate];

fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Post"];
fetchResult = [managedObjectContext() executeFetchRequest:fetchRequest error:nil];

NSLog(@"\n\n\nPredicate: %@", predicate);
NSLog(@"filteredRelationship: %@", filteredRelationship);
NSLog(@"fetchResult: %@", fetchResult);

// 4. Filtered relationship array is correct, fetch result is correct
predicate = [NSPredicate predicateWithFormat:@"(self.objectID IN %@)", @[ post.objectID ]];

filteredRelationship = [user.posts filteredSetUsingPredicate:predicate];

fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Post"];
fetchResult = [managedObjectContext() executeFetchRequest:fetchRequest error:nil];

NSLog(@"\n\n\nPredicate: %@", predicate);
NSLog(@"filteredRelationship: %@", filteredRelationship);
NSLog(@"fetchResult: %@", fetchResult);

TLDR输出

<redacted> Predicate: SELF IN {<Post: 0x2a04f10> (entity: Post; id: 0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1> ; data: { content = nil; title = nil; user = "0x2af2a20 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/User/p1>"; })}

<redacted> filteredRelationship: {(<Post: 0x2a04f10> (entity: Post; id: 0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1> ; data: { content = nil; title = nil; user = "0x2af2a20 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/User/p1>"; }) )}

<redacted> fetchResult: ("<Post: 0x2a04f10> (entity: Post; id: 0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1> ; data: {\n    content = nil;\n    title = nil;\n    user = \"0x2af2a20 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/User/p1>\";\n})")

<redacted> Predicate: SELF IN {0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1>}

<redacted> filteredRelationship: {()}

<redacted> fetchResult: ("<Post: 0x2a04f10> (entity: Post; id: 0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1> ; data: {\n    content = nil;\n    title = nil;\n    user = \"0x2af2a20 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/User/p1>\";\n})")

<redacted> Predicate: objectID IN {<Post: 0x2a04f10> (entity: Post; id: 0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1> ; data: { content = nil; title = nil; user = "0x2af2a20 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/User/p1>";})}

<redacted> filteredRelationship: {()}

<redacted> fetchResult: ("<Post: 0x2a04f10> (entity: Post; id: 0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1> ; data: {\n    content = nil;\n    title = nil;\n    user = \"0x2af2a20 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/User/p1>\";\n})")

<redacted> Predicate: objectID IN {0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1>} 

<redacted> filteredRelationship: {(<Post: 0x2a04f10> (entity: Post; id: 0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1> ; data: { content = nil; title = nil; user = "0x2af2a20 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/User/p1>";}))}

<redacted> fetchResult: ("<Post: 0x2a04f10> (entity: Post; id: 0x2a56c40 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/Post/p1> ; data: {\n    content = nil;\n    title = nil;\n    user = \"0x2af2a20 <x-coredata://9D07BF41-2DC0-42C1-9DD8-6082A00E7BEB/User/p1>\";\n})")

Answer 3

斯威夫特3解决方案

我遇到了同样的情况，因此我在下面发布了 swift 3 解决方案

let predicate = NSPredicate(format:"NOT (self IN %@)",[arrayofNSManagedObjects])