使用 returns 元组的函数更新地图列表

Question

我正在使用 Elixir 1.8.0 和 Ecto 3.0.7

我有一个看起来像这样的地图列表

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"
  }
]

我正在尝试使用 Ecto.Repo.insert_all 将此列表插入到我的数据库中。这不起作用，因为我将 launch_time 称为 utc_datetime 而这不是我列表中的 DateTime。

我试图将它转换为 DateTime，但是，from_iso8601 returns 一个元组，当然，它不起作用。

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"
  }
]

我怎样才能只在我的管道中取回 DateTime，以便我可以 insert_all 我的列表？还是这需要多个步骤？

Answer 1

您现有的代码稍作改动即可使用，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

虽然肯定可以 Enum.map/2，但惯用且更灵活的方法是使用 Access 行为（Access.all/0 for lists,) and 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))）如果所有输入数据都被证明是有效的。

使用 returns 元组的函数更新地图列表

Update list of maps with function that returns tuple

elixir

ecto

phoenix-framework