ugh

db.ex

# needed to get defdatabase and other macros
use Amnesia

# defines a database called Database, it's basically a defmodule with
# some additional magic
defdatabase Database do
  # this is just a forward declaration of the table, otherwise you'd have
  # to fully scope User.read in Message functions
  deftable User

  # this defines a table with an user_id key and a content attribute, and
  # makes the table a bag; tables are basically records with a bunch of helpers
  deftable Message, [:user_id, :content], type: :bag do
    # this isn't required, but it's always nice to spec things
    @type t :: Message[user_id: integer, content: String.t]

    # this defines a helper function to fetch the user from a Message record
    def user(self) do
      User.read(self.user_id)
    end

    # this does the same, but uses dirty operations
    def user!(self) do
      User.read!(self.user_id)
    end
  end

  # this defines a table with other attributes as ordered set, and defines an
  # additional index as email, this improves lookup operations
  deftable User, [:id, :name, :email], type: :ordered_set, index: [:email] do
    # again not needed, but nice to have
    @type t :: User[id: integer, name: String.t, email: String.t]

    # this is a helper function to add a message to the user, using write
    # on the created records makes it write to the mnesia table
    def add_message(content, self) do
      Message[user_id: self.id, content: content].write
    end

    # like above, but again with dirty operations, the bang methods are used
    # thorough amnesia to be the dirty counterparts of the bang-less functions
    def add_message!(content, self) do
      Message[user_id: self.id, content: content].write!
    end

    # this is a helper to fetch all messages for the user
    def messages(self) do
      Message.read(self.id)
    end

    # like above, but with dirty operations
    def messages!(self) do
      Message.read!(self.id)
    end
  end
end

gistfile1.txt

defmodule AmnesiaTest.Mixfile do
  use Mix.Project

  def project do
    [ app: :amnesia_test,
      version: "0.0.1",
      deps: deps ]
  end

  # Configuration for the OTP application
  def application do
    []
  end

  # Returns the list of dependencies in the format:
  # { :foobar, "0.1", git: "https://github.com/elixir-lang/foobar.git" }
  defp deps do
    [{:amnesia,"0.1.0",[github: "meh/amnesia", ref: "3dd03849a7f720f87e2cc3311ba04b0c4f63978d"]}]
  end
end
defmodule Mix.Tasks.Install do
   def run(_) do
     Amnesia.Schema.create
     Amnesia.start
     Database.create
     Database.wait
     Amnesia.stop
   end
 end

 defmodule Mix.Tasks.Uninstall do
   def run(_) do
     Amnesia.start
     Database.destroy
     Amnesia.stop
     Amnesia.Schema.destroy
   end
 end