Question

我需要一些帮助这个方法：

// deletes all points in database except points with given identifiers
- (void)deleteAllPointsExcept:(NSArray *)safeIdentifiers save:(BOOL)save {
    // create request to fetch all 'doomed' points
    NSManagedObjectContext *context = [[TSAppDelegate delegate] managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"MapPoint"];
    NSMutableArray *subpredicates = [NSMutableArray array];

    for (NSNumber *identifier in safeIdentifiers) {
        NSPredicate *pred = [NSPredicate predicateWithFormat:@"pid!=%@", identifier];
        [subpredicates addObject:pred];
    }
    fetchRequest.predicate = [NSCompoundPredicate andPredicateWithSubpredicates:subpredicates];

    // fetch 'em & destroy 'em
    NSError *error;
    NSArray *points = [context executeFetchRequest:fetchRequest error:&error];

    for (TSMapPoint *point in points) {
        [context deleteObject:point];
    }

    // save if requested
    if (save) {
        [[[TSAppDelegate delegate] managedObjectContext] save:NULL];
    }
}

它应该从我的核心数据NSManagedObjectContext中清除不需要的MapPoints。它工作正常，但有一天我收到了这条消息：

CoreData: error: (1) I/O error for database at ...  SQLite error code:1, 'Expression tree is too large (maximum depth 1000)'

我已经搜索过，当谓词太长，如WHERE id=1 OR id=2 OR id=3 ...时，会发生这种情况，但我不知道如何解决这个问题。有人有想法吗？

提前致谢，皮特。

Answer 1

您的谓词应简化为以下内容

[NSPredicate predicateWithFormat:@"NOT (pid IN %@)", safeIdentifiers];

Answer 2

如果标识符太多，则无法在SQL命令中直接使用它们（无论您是否使用参数）。

您必须将所有ID写入临时表，然后使用检查该表的单个谓词：

DELETE FROM PointsTable WHERE pid NOT IN MyTempTable

核心数据：表达式树太大

2 个答案: