使用Elixir中的地图访问列表中的嵌套元素

Question

I am new to elixir an phoenix an got some problems accessing nested elements inside a test. I am testing a controller and got so far following response:

.[%{"attributes" => %{"first_name" => "Timmy 96", "last_name" => 
"Assistant"},
"id" => "bca58c53-7c6e-4281-9bc8-0c4616a30051",
"relationships" => %{"avatar" => %{"data" => %{"id" => "011300fd-ca98-42b4-
9561-f1cdc93d2d25",
"type" => "pictures"}}}, "type" => "users"}]

I am using JSON-API-format for the response and am fetching the attributes with userdata:

user_attr = Enum.filter(includes, fn(item)->
    item["relationships"]["avatar"] != nil
end)
IO.inspect user_attr
case Enum.fetch(user_attr ,0) do
  {:ok, value} ->
    assert value["attributes"]["first_name"] == user.first_name
    assert value["attributes"]["last_name"] == user.last_name
  {_} ->
    assert false
end

I want to shorten this part, dont want to use a case, but no idea how to get the value of the user_attr without using the value part in the case.

I would also want to asser the id of the relationships -> avatar -> data -> id with the id I inserted before, but no idea how to access this value. The id is part of the picture i inserted before so I would like to

assert XXX == picture.id

But how to get the XXX?

Hope someone can help me. Last years only Java and C#, never Ruby and now I got somehow into elixir :/

Thanks.

Answer 1

You should try using pattern matching more.

# fixture data.
user = %{first_name: "Timmy 96", last_name: "Assistant"}
picture = %{id: "011300fd-ca98-42b4-\n9561-f1cdc93d2d25"}
value = %{
      "attributes" => %{"first_name" => "Timmy 96", "last_name" => "Assistant"},
      "id" => "bca58c53-7c6e-4281-9bc8-0c4616a30051",
      "relationships" => %{
        "avatar" => %{
          "data" => %{
            "id" => "011300fd-ca98-42b4-\n9561-f1cdc93d2d25",
            "type" => "pictures",
          },
        },
      },
      "type" => "users",
    }

assert %{"attributes" => attributes} = value
# ensure the expected value match with actual value and than bind the attributes variable with actual attributes map.
assert %{"first_name" => user.first_name, "last_name" => user.last_name} == attributes

assert %{"relationships" => %{"avatar" => %{ "data" => avatar_data}}} = value
assert %{"id" => picture.id, "type" => "pictures"} == avatar_data

One of Elixir's most powerful features is pattern matching via the = operator(match operator).

The above example shows you that we can use match operator to assert that the data structures of expected value match with actual value.

Learn more about testing and pattern matching: https://semaphoreci.com/community/tutorials/introduction-to-testing-elixir-applications-with-exunit

Answer 2

You can use get_in/2 to do this.

iex()> list
[%{"attributes" => %{"first_name" => "Timmy 96", "last_name" => 
"Assistant"},
"id" => "bca58c53-7c6e-4281-9bc8-0c4616a30051",
"relationships" => %{"avatar" => %{"data" => %{"id" => "011300fd-ca98-
42b4-\n9561-f1cdc93d2d25",
     "type" => "pictures"}}}, "type" => "users"}]

iex()> [map] = list
[%{"attributes" => %{"first_name" => "Timmy 96", "last_name" => 
"Assistant"},
"id" => "bca58c53-7c6e-4281-9bc8-0c4616a30051",
"relationships" => %{"avatar" => %{"data" => %{"id" => "011300fd-ca98-
42b4-\n9561-f1cdc93d2d25",
     "type" => "pictures"}}}, "type" => "users"}]


iex()> get_in map, ["attributes", "first_name"]
"Timmy 96"
iex()> get_in map, ["attributes", "last_name"]
"Assistant"
iex()> get_in map, ["relationships", "avatar", "data", "id"]
"011300fd-ca98-42b4-\n9561-f1cdc93d2d25"