Question

我有一个必需的键列表（required_keys）：

["artist", "track", "year"]

和地图（参数）：

%{"track" => "bogus", "artist" => "someone"}

我想确定params是否有required_keys。我来自Ruby背景并且迭代似乎对Elixir不合适，但不确定如何进行模式匹配来做到这一点。

Answer 1

使用Enum.all?/2和Map.has_key?/2：

iex(1)> map = %{"track" => "bogus", "artist" => "someone"}
%{"artist" => "someone", "track" => "bogus"}
iex(2)> map2 = %{"track" => "bogus", "artist" => "someone", "year" => 2016}
%{"artist" => "someone", "track" => "bogus", "year" => 2016}
iex(3)> required_keys = ["artist", "track", "year"]
["artist", "track", "year"]
iex(4)> Enum.all?(required_keys, &Map.has_key?(map, &1))
false
iex(5)> Enum.all?(required_keys, &Map.has_key?(map2, &1))
true

但不确定如何进行模式匹配

如果required_keys是动态的，则无法进行模式匹配。如果它是静态列表，您可以使用模式匹配：

iex(6)> match?(%{"artist" => _, "track" => _, "year" => _}, map)
false
iex(7)> match?(%{"artist" => _, "track" => _, "year" => _}, map2)
true

Answer 2

requireds = ["artist", "track", "year"]
params = %{"track" => "bogus", "artist" => "someone"}
Enum.all?( requireds, fn(k) -> Map.has_key?(params, k) end) # => false
requireds = ["artist", "track"]
Enum.all?( requireds, fn(k) -> Map.has_key?(params, k) end) # => true

或模式匹配：

def has_required_params?(%{"artist" => _, "track" => _, "year" => _}), do: true
def has_required_params?(_), do: false

has_required_params?(%{"track" => "bogus", "artist" => "someone"}) # => false
has_required_params?(%{"track" => "bogus", "artist" => "someone", year => "2000"}) # => true

Answer 3

使用in代替Map.has_key?：

def contains_fields?(keys, fields), do: Enum.all?(fields, &(&1 in keys))

来自https://elixirschool.com/en/lessons/specifics/plug/

确定Map是否具有某些键的正确方法

3 个答案: