"Using application configuration for libraries" added (Anti-patterns documentation)

[lucasvegi]

No description provided.

[whatyouhide]

One suggestion I have is to simulate a slightly more complex example that however can be significantly more realistic.

My go to is once again something where the antipattern is configuring for example a base URL through app config

config :api_client,
  base_url: "..."

and the refactoring would be to pass it as an option:

APIClient.request(..., base_url: "...")

[lucasvegi]

@whatyouhide What do you think of this example? If it's cool I'll adapt the text with a new commit

import Config

config :api_client,
  base_url: "https://api.github.com"

import_config "#{config_env()}.exs"

defmodule APIClient do
  def request(endpoint) when is_binary(endpoint) do
    HTTPoison.start
    base_url = Application.fetch_env!(:api_client, :base_url)  # <= retrieve parameterized value
    HTTPoison.get(base_url <> endpoint)                        # <= base_url: "https://api.github.com"
  end
end

#...Use examples with anti-pattern

iex> APIClient.request("/users/lucasvegi")  #<== OK!
{:ok,
 %HTTPoison.Response{
   status_code: 200,
   body: "...",
   headers: [ ... ],
   request_url: "https://api.github.com/users/lucasvegi",
   ...
 }}

iex> APIClient.request("/persons?_quantity=1")  #<== Failed attempt to access a different API!
{:ok,
 %HTTPoison.Response{
   status_code: 404,
   body: "{\"message\":\"Not Found\",\"documentation_url\":\"https://docs.github.com/rest\"}",
   headers: [ ... ],
   request_url: "https://api.github.com/persons?_quantity=1",  # <== base_url never changes!
   ...
 }}

Refactoring:

defmodule APIClient do
  def request(endpoint, options \\ []) when is_binary(endpoint) and is_list(options) do
    HTTPoison.start
    base_url = Keyword.get(options, :base_url, "https://api.github.com")  # <= default config of base_url == "https://api.github.com"
    HTTPoison.get(base_url <> endpoint)
  end
end

#...Use examples of the refactored code

iex> APIClient.request("/users/lucasvegi")  #<== OK with default config!
{:ok,
 %HTTPoison.Response{
   status_code: 200,
   body: "...",
   headers: [ ... ],
   request_url: "https://api.github.com/users/lucasvegi",
   ...
 }}

iex> APIClient.request("/persons?_quantity=1", [base_url: "https://fakerapi.it/api/v1"]) #<== OK with another API!
{:ok,
%HTTPoison.Response{
  status_code: 200,
  body: "{...\"data\":[{\"id\":1,\"firstname\":\"Taryn\",\"lastname\":\"Price\",...}",
  headers: [ ... ],
  request_url: "https://fakerapi.it/api/v1/persons?_quantity=1",
  ...
}}

[whatyouhide]

@lucasvegi yes that's exactly what I had in mind. Few notes:

• We don't need to mention HTTPoison specifically. Let's replace it with MyApp.HTTPClient.
• We don't need to be verbose when showing return values as you do in your example, as it's not what we're talking about here.

Does that make sense?

[lucasvegi]

def request(endpoint) when is_binary(endpoint) do
    HTTPoison.start
    base_url = Application.fetch_env!(:api_client, :base_url)  # <= retrieve parameterized value
    HTTPoison.get(base_url <> endpoint)                        # <= base_url: "https://api.github.com"
  end

So the definition of the request function would look something like this?

  def request(endpoint ...) do
    base_url = ...
    MyApp.HTTPClient.get(base_url <> endpoint)
  end

[whatyouhide]

@lucasvegi yep!

[lucasvegi]

@lucasvegi yep!

Great! I'll make some adjustments and commit

[josevalim]

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