简化多次获取请求

Question

我有这个核心数据模型层次结构，彼此之间具有相应的关系：

公司 - ＆gt; DIVISIONS - ＆gt;部门 - ＆gt;员工 - ＆gt;照片

如果我想收集分部的所有员工照片，我需要：

1. 抓取以查找哪些部门有分部。
2. 抓取以找到该部门每个部门的所有员工
3. 获取每位员工以查找是否有照片....
4. 将照片添加到阵列。

在循环中有3个请求，性能明智是一个灾难！

-(NSArray *)getPhotosForCategory: (NSManagedObject *)division {

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Divisions"];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"division == %@", department];
    [request setPredicate:predicate];

    NSError *error;
    divisions = [managedObjectContext executeFetchRequest:request error:&error];

    NSMutableArray *employeesArray = [[NSMutableArray alloc] init];

    for (NSManagedObject *object in divisions) {

        NSFetchRequest *employeesRequest = [NSFetchRequest fetchRequestWithEntityName:@"Employees"];
        NSPredicate *employeesPredicate = [NSPredicate predicateWithFormat:@"department == %@", object];
        [employeesRequest employeesPredicate];

        NSArray *employees = [managedObjectContext executeFetchRequest:employeesRequest error:&error];

        [employeesArray addObjectsFromArray:places];

    }

    NSMutableArray *photosArray = [[NSMutableArray alloc] init];

    for (NSManagedObject *object in employeesArray) {

        NSFetchRequest *photosRequest = [NSFetchRequest fetchRequestWithEntityName:@"Photos"];
        NSPredicate *photosPredicate = [NSPredicate predicateWithFormat:@"employee == %@", object];
        [photosRequest setPredicate:photosPredicate];

        NSArray *photos = [managedObjectContext executeFetchRequest:photosRequest error:&error];

        [photosArray addObjectsFromArray:photos];

    }

    return photosArray;

}

任何人都可以建议更好的解决方案或如何完成此类请求？

Answer 1

假设您为所有内容设置了反向关系：

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Photos"];    
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"employee.department.division = %@", division"];