NSPredicate 与 FUNCTION 不工作

问题描述

我的谓词不断使我的应用程序崩溃，并显示消息 Unsupported function expression FUNCTION(SELF, "filterDistanceWithLatitude:" , latitude, longitude).有谁知道如何解决这个问题?

My predicate keeps on crashing my app with the message Unsupported function expression FUNCTION(SELF, "filterDistanceWithLatitude:" , latitude, longitude). Does anyone know how to fix this?

- (void)setUpFetchedResultsController
{
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"NextTime"]; //Retrieve data for the place entity
    request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)]]; //How to sort it
    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:self.context sectionNameKeyPath:nil cacheName:nil]; //Puts the data in a NSFetchedResultsController which is oddly located in CoreDataTableViewController //Puts the data in a NSFetchedResultsController which is oddly located in CoreDataTableViewController
    self.filtered = self.fetchedResultsController.fetchedObjects;
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"FUNCTION(self, 'filterByDistanceWithLatitude:', latitude, longtitude) > 20"];
    self.filtered = [self.filtered filteredArrayUsingPredicate:predicate];
}

- (double)filterByDistanceWithLatitude:(NSNumber *)latitude andLongitude:(NSNumber *)longitude
{
    CLLocationDegrees latitudeCoor = [latitude doubleValue]; //Puts the latitude into a NextTime object.
    CLLocationDegrees longitudeCoor = [longitude doubleValue]; //Puts the longtitude into a NextTime object.

    CLLocation *loc1 = [[CLLocation alloc] initWithLatitude:latitudeCoor longitude:longitudeCoor];
    CLLocation *loc2 = [[CLLocation alloc] initWithLatitude:self.currentLocation.latitude longitude:self.currentLocation.longitude];

    NSNumber *distance = [[NSNumber alloc] initWithDouble:[loc1 distanceFromLocation:loc2]];

    return [distance doubleValue];
}

推荐答案

(基于 SQL 的)核心数据存储的提取请求不能使用基于 Objective-C 的谓词或排序描述符.您只能过滤存储在数据库中的属性.

A fetch request for a (SQL based) Core Data store cannot use Objective-C based predicates or sort descriptors. You can only filter on attributes stored in the data base.

这里是《核心数据编程指南》中的相关文档:

Here is the relevant documentation from the "Core Data Programming Guide":

• 获取托管对象:

您不能使用基于瞬态属性的谓词来获取(虽然你可以使用瞬态属性在内存中过滤你自己).... 总而言之，如果您直接执行 fetch，您应该通常不会将基于 Objective-C 的谓词或排序描述符添加到获取请求.相反，您应该将这些应用于结果获取.

• 获取谓词和排序描述符:

获取和存储类型之间存在一些交互作用.... SQL 存储，另一方面，编译谓词和排序描述符到 SQL 并在数据库本身中评估结果.这样做主要是为了性能，但这意味着评估发生在非 Cocoa 环境中，因此排序描述符(或谓词)依赖 Cocoa 无法工作.

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