Reusing swagger parameters

When building an API it can be common to have headers or parameters that are common to multiple actions.

Scenario

For example, let's say we've got two endpoints:

• GET /projects
• GET /books

Both of these endpoints can be sorted using by sort_by and sort_direction parameters and both require an Authorization header.

Here's what the swagger spec in our ProjectsController would look like:

defmodule ProjectsController do
  use PhoenixSwagger

  swagger_path :index do
    get "/projects"
    produces "application/json"
    parameter("Authorization", :header, :string, "OAuth2 access token", required: true)
    parameters do      
      sort_by :query, :string, "The property to sort by"
      sort_direction :query, :string, "The sort direction", enum: [:asc, :desc], default: :asc
      company_id :string, :query, "The company id"
    end
  end
end

Our BooksController swagger would look very similar, also defining the Authorization header and the sort_by and sort_direction headers.

Extracting parameters into a module for reuse

The swagger_path macro layer is actually just some syntactic sugar over regular elixir functions, intended to be easily extended. Any function that accepts a %PhoenixSwagger.Path.PathObject{} as its first argument and returns an updated %PathObject{} can be used in the swagger_path macro.

Knowing this, we can easily extract some of the common logic into a module and reuse it in our controllers.

defmodule CommonParameters do
  @moduledoc "Common parameter declarations for phoenix swagger"

  alias PhoenixSwagger.Path.PathObject
  import PhoenixSwagger.Path

  def authorization(path = %PathObject{}) do
    path |> parameter("Authorization", :header, :string, "OAuth2 access token", required: true)
  end

  def sorting(path = %PathObject{}) do
    path
    |> parameter(:sort_by, :query, :string, "The property to sort by")
    |> parameter(:sort_direction, :query, :string, "The sort direction", enum: [:asc, :desc], default: :asc)
  end
end

This can also be done using the parameters macro:

def sorting(path = %PathObject{}) do
  parameters path do
    sort_by :query, :string, "The property to sort by"
    sort_direction :query, :string, "The sort direction", enum: [:asc, :desc], default: :asc
  end
end

Reusing the common parameters

Now, instead of defining these parameters in every controller, we can just reference the CommonParameters module:

defmodule ProjectsController do
  use PhoenixSwagger

  swagger_path :index do
    get "/users"
    produces "application/json"
    CommonParameters.authorization
    CommonParameters.sorting
    parameters do
      company_id :string, :query, "The company id"
    end
  end
end