coredata - 将一个属性提取到数组中

Question

目标：我想从数据库（核心数据）中获取一个属性（来自实体）的值到一个数组中。

示例

实体名称 = 员工

属性 = 员工 ID

我只想将所有的employeeID 填充到一个数组/集合中。

问题

鉴于下面是我的实现，我只是觉得这是一种迂回的方式，我想知道是否有更好的方法来做到这一点。

代码

NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Employees"];

fetchRequest.resultType = NSDictionaryResultType;

[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:@"employeeID", nil]];

NSError *error      = nil;
NSArray *results    = [self.managedObjectContext executeFetchRequest:fetchRequest
                                                               error:&error];

NSMutableArray *employeeIDs = [NSMutableArray array];

for(id currentRecord in results)
{
    [employeeIDs addObject:[currentRecord objectForKey:@"employeeID"]];
}

Answer 1

你可以避免最后一个for循环，

而不是，

NSMutableArray *employeeIDs = [NSMutableArray array];

for(id currentRecord in results)
{
    [employeeIDs addObject:[currentRecord objectForKey:@"employeeID"]];
}

试试这个，

NSMutableArray *employeeIDs = [results valueForKey:@"employeeID"];

Answer 2

一种方法是-

NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Employees"];
fetchRequest.resultType = NSDictionaryResultType;

NSError *error      = nil;
NSArray *results    = [self.managedObjectContext executeFetchRequest:fetchRequest
                                                               error:&error];

NSMutableArray *employeeIDs = [results valueForKey:@"employeeID"];