Tarams

Tarams provides a simple way for parsing request params with predefined schema

• Installation
• Usage
• Set default value
• Custom cast function
• API Documentation

Installation

Available in Hex, the package can be installed by adding tarams to your list of dependencies in mix.exs:

def deps do
  [
    {:tarams, "~> 0.2.0"}
  ]
end

Usage

@index_params_schema  %{
    keyword: :string,
    status: [type: string, required: true],
    group_id: [type: :integer, validate: {:number, [greater_than: 0]}]
  }

def index(conn, params) do
    with {:ok, better_params} <- Tarams.parse(@index_params_schema, params) do
        # do anything with your params
    else
        {:error, changset} -> # return params error
    end
end

Default value

You can define default value for a field if it is missing in params

schema = %{
    status: [type: :string, default: "pending"]
}

Or you can define default value as a function. This function is evaluated each time invoke Tarams.parse

schema = %{
    date: [type: :utc_datetime, default: &Timex.now/0]
}

Custom cast function

By default Tarams uses Ecto.Changeset to cast built-in types. If you don't want to use default casting functions, or you want define casting function for custom type, tarams provide cast_func option to define a custom cast function. This is cast_func spec fn(any) :: {:ok, any} | {:error, binary}

If cast_func returns {:ok, value} this value is added to changeset If it returns {:error, message}, error message is added to changeset errors

def my_array_parser(value) do
    if is_binary(value) do
        ids = 
            String.split(value, ",")
            |> Enum.map(&String.to_integer(&1))
        
        {:ok, ids}
    else
        {:error, "Invalid string"
    end
end

schema = %{
    user_id: [type: {:array, :integer}, cast_func: &my_array_parser/1]
}

Tarams.parse(schema, %{user_id: "1,2,3"})

This is a demo parser function.

Why Tarams

I looked for a library for parsing phoenix request params, and I found params. It is an awesome library but it does not support params validation.

I clone the source code and try to make some change to support validation but macro world is soo complicated. Then I decide to write my own library that support parsing and validating parameter and without macro ( after I red the book Metaprogramming in Elixir). So you can read the source code ( it is quite simple) and modify it to fit your need.

Contributors

If you find a bug or want to improve something, please send a pull-request. Thank you!