与功能的地图更新列表返回元组

Question

我使用的药剂1.8.0和3.0.7外生

我有地图的列表，看起来像这样

things = [
  %{
    availability_zone: "us-west-1a",
    dns_name: "ec2-13-45-67-46.us-west-1.compute.amazonaws.com",
    image_id: "ami-251234",
    instance_id: "i-1234",
    instance_state: "running",
    instance_type: "m4.large",
    ip_address: "13.45.67.46",
    key_name: "some_key",
    launch_time: "2018-06-13T16:34:04.000Z",
    monitoring: "disabled",
    private_ip_address: "10.1.1.1",
    vpc_id: "vpc-9999"
  },
  %{
    availability_zone: "us-west-1a",
    dns_name: "ec2-13-99-99-46.us-west-1.compute.amazonaws.com",
    image_id: "ami-2522344",
    instance_id: "i-99999",
    instance_state: "running",
    instance_type: "m4.large",
    ip_address: "13.99.99.99",
    key_name: "some_key",
    launch_time: "2018-06-13T16:34:04.000Z",
    monitoring: "disabled",
    private_ip_address: "10.1.1.2",
    vpc_id: "vpc-9999"
  }
]

我试图插入此列表到我的数据库使用Ecto.Repo.insert_all。这并不是因为是工作，因为我打电话launch_time一个utc_datetime，这是不是在我的列表中的日期时间。

我试图将其转换为DateTime，然而，from_iso8601返回一个元组，其中，当然，不能正常工作。

iex(12)> things |> Enum.map(fn elem ->
...(12)>         Map.update!(elem, :launch_time, &DateTime.from_iso8601/1)
...(12)>       end)
[
  %{
    availability_zone: "us-west-1a",
    dns_name: "ec2-13-56-179-46.us-west-1.compute.amazonaws.com",
    image_id: "ami-25110f45",
    instance_id: "i-0df401bc2d3b16d37",
    instance_state: "running",
    instance_type: "m4.large",
    ip_address: "13.56.179.46",
    key_name: "salt_provisioning",
    launch_time: {:ok, #DateTime<2018-06-13 16:34:04.000Z>, 0},
    monitoring: "disabled",
    private_ip_address: "10.81.1.244",
    vpc_id: "vpc-07a5e160"
  },
  %{
    availability_zone: "us-west-1a",
    dns_name: "ec2-13-56-179-46.us-west-1.compute.amazonaws.com",
    image_id: "ami-25110f45",
    instance_id: "i-0df401bc2d3b16d37",
    instance_state: "running",
    instance_type: "m4.large",
    ip_address: "13.56.179.46",
    key_name: "salt_provisioning",
    launch_time: {:ok, #DateTime<2018-06-13 16:34:04.000Z>, 0},
    monitoring: "disabled",
    private_ip_address: "10.81.1.244",
    vpc_id: "vpc-07a5e160"
  }
]

我怎样才能得到公正的日期时间回到我管，这样我可以insert_all我的名单？或者，这是否需要多个步骤？

Answer 1

您现有的代码可以做一个小的变化工作，希望它符合您的要求：

things |> Enum.map(fn elem ->
  {:ok, datetime, _} = DateTime.from_iso8601(elem[:launch_time])
  Map.put(elem, :launch_time, datetime)
end)

Answer 2

虽然一个肯定会Enum.map/2，惯用和更灵活的方式是使用Access行为（Access.all/0的列表）和Kernel.get_and_update_in/3：

get_and_update_in(things, [Access.all(), :launch_time], fn prev ->
  {prev, with {:ok, neu, _} <- DateTime.from_iso8601(prev), do: neu}
end) 

（或(prev |> DateTime.from_iso8601() |> elem(1))）如果所有的输入数据被证明是有效的。