领域-返回数组列表

我有一个名为mood的领域对象,我试图以[字符串]列表的形式返回字段活动中的所有值,其中mood=great

我的领域对象看起来像:

Results<Mood> <0x7fce164851a0> (
    [0] Mood {
        mood = Great;
        comment = test;
        activities = Friends;
        time = 8:06 PM;
        date = 4/10/18;
        symptom = down;
    },
    [1] Mood {
        mood = Sad;
        comment = ;
        activities = Date;
        time = 6:22 PM;
        date = 4/14/18;
        symptom = up;
    },
    [2] Mood {
        mood = Sad;
        comment = ;
        activities = Date;
        time = 7:40 PM;
        date = 4/14/18;
        symptom = Night;
    },
    [3] Mood {
        mood = Sad;
        comment = ;
        activities = Date;
        time = 7:41 PM;
        date = 4/14/18;
        symptom = Dry;
    },
    [4] Mood {
        mood = Awful;
        comment = this is an example data for the app!;
        activities = Date;
        time = 2:17 PM;
        date = 4/15/18;
        symptom = Lost;
    }
)

我想返回如下列表

[“向下”] 因为这是一项情绪=良好等的活动

我尝试过:

func getGreatMoodActivity() -> [String]{
    let greaMoodActivity = Set(realm.objects(Mood.self).filter("mood = 'Great'") as! [String])
    return getGreatMoodActivity()
}

但这个错误导致了崩溃

无法强制转换“RealmSwift”类型的值。结果' (0x10f520810)至“NSArray”(0x10ce35008)。

有没有办法解决这个问题?