ParamsNormalizer

Provides a mechanism for normalizing params in phoenix controllers.

Example usage:

    import ParamsNormalizer

    action_fallback MyActionFallbackController

    def index(conn, params)
      process_params_func = fn ->
        process = [
          %{path: ["data", "attributes", "id"], process: &string_to_integer/1}
        ]

        validate_and_normalize_params(params, process)
      end

      execute_func = fn(id) ->
        data = MyModule.call(id)

        render(conn, MyView, "index.json", %{data: data})
      end

      with {:ok, %{"data" => %{"attributes" => %{"id" => id}}} <- process_params_func.(params),
      do: execute_func.(id)
    end

Here we are using a consistent pattern in our controllers. We have one function, process_params_func and an execute_func.

The process_params_func makes a call to the validate_and_normalize_params, passing it a list of maps, containing a path to the params to be validated and a function to validate and normalize.

This function needs to return an {:ok, value} which will be put back into the params in the same place it was passed in (see details for more information)

If any of the validations return an error, the with function won't execute and the action_fallback call function will be called.

In your action_fallback plug you will need to implement a function which will handle a def call(conn, {:error, :invalid_params, errors}

Rationale

The controller may get slightly larger here with the actions, however it provides a consistent format that becomes easier to read.

Basically, when looking at an action you can see at the top what and how the params are going to be processed as well as what action will be executed if the params are successfully validated.

Details

Below shows how the validate_and_normalize_params function works.

Takes in a list of maps.

Each map has a :path key with is a path to the value to be proccess.

E.g. if you wanted to process "id" in:

iex> %{
  "data" => %{
    "attributes" => %{
      "id" => "3"
    }
  }
}

The path would look like: ["data", "attributes", "id"]

The second k/v pair is a function that takes in the value and either returns {:ok, processed_value} or {:error, "reason"}

This procced value will be put back into the same position as it was retrieved from.

E.g.

iex> validations = [
  %{path: ["data", "attributes", "id"], process: &string_to_integer/1}
]

iex> params = %{
  "data" => %{
    "attributes" => %{
      "id" => "3"
    }
  }
}

iex> ParamsNormalizer.validate_and_normalize_params(params, validations)
  {:ok, %{
    "data" => %{
      "attributes" => %{
        "id" => 3
      }
    }
  }

iex> params = %{
  "data" => %{
    "attributes" => %{
      "id" => ["3"]
    }
  }
}

iex> ParamsNormalizer.validate_and_normalize_params(params, validations)
  {:error, :invalid_params, %{"data.attributes.id" => "can't be cast to integer"}}

Installation

def deps do
  [
    {:params_normalizer, github: "myxplor/params-normalizer.git"}
  ]
end