如何在 Elixir 中修改地图

Question

创建了 JSON api

我的控制器中有一个用于创建操作的端点，它采用 json 如下所示的数据：

     [{"opens_detail"=>
          [{"ua"=>"Linux/Ubuntu/Chrome/Chrome 28.0.1500.53",
              "ip"=>"55.55.55.55",
              "ts"=>1365190001,
              "location"=>"Georgia, US"}],
         "template"=>"example-template",
         "metadata"=>{"user_id"=>"123", "website"=>"www.example.com"},
         "clicks"=>42,
         "ts"=>1365190000,
         "state"=>"sent",
         "clicks_detail"=>
          [{"ua"=>"Linux/Ubuntu/Chrome/Chrome 28.0.1500.53",
              "ip"=>"55.55.55.55",
              "ts"=>1365190001,
              "url"=>"http://www.example.com",
              "location"=>"Georgia, US"}],
         "email"=>"recipient.email@example.com",
         "subject"=>"example subject",
         "sender"=>"sender@example.com",
         "_id"=>"abc123abc123abc123abc123",
         "tags"=>["password-reset"],
         "opens"=>42}]

我的目标是利用这个 json 并从中创建一个新的，其中一些键和值被重命名以匹配我下面的模式：

在web/models/messages.ex

   ...
      schema "messages" do
        field :sender, :string
        field :uniq_id, :string # equal to '_id' in the payload
        field :ts, :utc_datetime
        field :template, :string
        field :subject, :string
        field :email, :string
        field :tags, {:array, :string}
        field :opens, :integer
        field :opens_ip, :string # equal to nested 'ip' value in 'open_details'
        field :opens_location, :string # equal to nested 'location' value in 'open_details'
        field :clicks, :integer
        field :clicks_ip, :string # equal to nested 'ip' value in 'click_details'
        field :clicks_location, :string # equal to nested 'location' value in 'click_details'
        field :status, :string # equal to the "state" in the payload

        timestamps()
      end
  ...

这是我试过的：

在web/controller/message_controller.ex:

  def create(conn, payload) do

    %{ payload |
      "uniq_id" => payload["_id"],
      "status" => payload["type"]
      "open_ips" =>  Enum.at(payload["opens_detail"], 0)['ip'],
      "open_location" => Enum.at(payload["opens_detail"], 0)['location'],
      "click_ips" =>  Enum.at(payload["clicks_detail"], 0)['ip'],
      "click_location" => Enum.at(payload["clicks_detail"], 0)['location'],
    }

    changeset = Message.changeset(%Message{}, payload)

   ...

  end

但很快我就发现它不起作用，因为我仍然需要删除一些密钥。

我来自 Ruby/Python (Rails/Django)，不想用我的 OO 知识开始污染我对函数式编程的学习，特别是 elixir/phoenix。

你会如何解决这个问题？

Answer 1

How would you solve this problem?

我会从头开始创建新地图，而不是更新原始地图。您可以使用 get_in 来简化访问嵌套字段的逻辑。这是一个例子：

map = %{
  uniq_id:        get_in(payload, ["_id"]),
  open_ips:       get_in(payload, ["opens_detail", Access.at(0), "ip"]),
  open_locations: get_in(payload, ["opens_detail", Access.at(0), "location"]),
}

如果要从原始地图中选择字段的子集，可以使用 Map.merge 和 Map.take:

Map.merge(Map.take(payload, [:sender, ...]), %{uniq_id: ...})

但如果只有几个字段，我宁愿手动写出来。

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