ios - 快速总结 Realm 对象数组中的属性

Question

有两个realm对象类，一个是Entry，另一个是Work。模型场景如下所示。Entry 类为

open class Entry: Object {
  dynamic open var date = Entry.defaultDate()
  dynamic open var quantity = 0.0
  dynamic open var percentage = 0.0
  dynamic open var goal = 0.0
  open let gulps = List<Work>()
}

Work 类如下所示。

open class Work: Object {
  dynamic var quantity = 0.0
  dynamic var type = 0
}

插入一些数据后，一个 Entry 对象如下所示。

(Entry {
    date = 2017-11-29;
    quantity = 1.193675890564919;
    percentage = 59.68379452824593;
    goal = 2;
    gulps = RLMArray <0x6040000e7800> (
        [0] Work {
            quantity = 0.5;
            type = 0;
        },
        [1] Work {
            quantity = 0.5;
            type = 1;
        },
        [2] Work {
            quantity = 0.09683794528245926;
            type = 0;
        },
        [3] Work {
            quantity = 0.09683794528245926;
            type = 2;
        }
    );
})

现在我正在尝试创建一个数组，其中包含根据 Work 类型的总数量，其中数组索引根据 Work 类型。因此该条目的数组应该是。

[0.59683,0.5,0.09683794528245926]

那么如何有效地生成这个数组呢？

Answer 1

这应该相当简单，定义一个与数量属性匹配的类型数组，然后循环遍历返回数量的 gulps 数组

let workArray: [Double] = entry.gulps.map({ return $0.quantity })

map 函数将迭代列表中的每个项目，并运行您在大括号之间定义的闭包，在这种情况下，它将迭代每个工作项目并仅返回数量。

您可以了解更多 map 功能here或者苹果官方文档是 here

这是我在 Playground 上编写的完整工作示例

struct Entry {

    var quantity = 0.0
    var percentage = 0.0
    var goal = 0.0
    var gulps = [Work]()
}

struct Work {
    var quantity = 0.0
    var type = 0
}

let work1 = Work(quantity: 1.0, type: 5)
let work2 = Work(quantity: 2.0, type: 5)
let work3 = Work(quantity: 4.0, type: 5)
let work4 = Work(quantity: 6.0, type: 5)

let entry = Entry(quantity: 5.0, percentage: 50.0, goal: 60.0, gulps: [
    work1,
    work2,
    work3,
    work4
])

let workArray: [Double] = entry.gulps.map({ return $0.quantity })
print(workArray)

Output: [1.0, 2.0, 4.0, 6.0]