Commandex
Make Elixir actions a first-class data type.
Commandex structs are a loose implementation of the command pattern, making it easy to wrap parameters, data, and errors into a well-defined struct.
Installation
Add commandex as a mix.exs dependency:
def deps do
[
{:commandex, "~> 0.4.1"}
]
endExample Usage
A fully implemented command module might look like this:
defmodule RegisterUser do
import Commandex
command do
param :email
param :password
data :password_hash
data :user
pipeline :hash_password
pipeline :create_user
pipeline :send_welcome_email
end
def hash_password(command, %{password: nil} = _params, _data) do
command
|> put_error(:password, :not_given)
|> halt()
end
def hash_password(command, %{password: password} = _params, _data) do
put_data(command, :password_hash, Base.encode64(password))
end
def create_user(command, %{email: email} = _params, %{password_hash: phash} = _data) do
%User{}
|> User.changeset(%{email: email, password_hash: phash})
|> Repo.insert()
|> case do
{:ok, user} -> put_data(command, :user, user)
{:error, changeset} -> command |> put_error(:repo, changeset) |> halt()
end
end
def send_welcome_email(command, _params, %{user: user}) do
Mailer.send_welcome_email(user)
command
end
endThe command/1 macro will define a struct that looks like:
%RegisterUser{
success: false,
halted: false,
errors: %{},
params: %{email: nil, password: nil},
data: %{password_hash: nil, user: nil},
pipelines: [:hash_password, :create_user, :send_welcome_email]
}As well as two functions:
&RegisterUser.new/1
&RegisterUser.run/1&new/1 parses parameters into a new struct. These can be either a keyword list
or map with atom/string keys.
&run/1 takes a command struct and runs it through the pipeline functions defined
in the command. Functions are executed in the order in which they are defined.
If a command passes through all pipelines without calling halt/1, :success
will be set to true. Otherwise, subsequent pipelines after the halt/1 will
be ignored and :success will be set to false.
Running a command is easy:
%{email: "example@example.com", password: "asdf1234"}
|> RegisterUser.new()
|> RegisterUser.run()
|> case do
%{success: true, data: %{user: user}} ->
# Success! We've got a user now
%{success: false, errors: %{password: :not_given}} ->
# Respond with a 400 or something
%{success: false, errors: _errors} ->
# I'm a lazy programmer that writes catch-all error handling
endFor even leaner implementations, you can run a command by passing
the params directly into &run/1 without using &new/1:
%{email: "example@example.com", password: "asdf1234"}
|> RegisterUser.run()
