mnesia.exs

# define a record, first attribute is considered the key
defrecord User, email: "", first: "", last: ""

# encapsulates mnesia calls
defmodule Database do
  def create_schema do
    create_table User
  end
  
  def find(record, id) do
    :mnesia.read(record, id) 
  end

  def write(object) do
    :mnesia.write(object)
  end

  def delete(user=User[]), do: nil # dont allow deleting user
  def delete(object) do # everything else ok to delete :)
    :mnesia.delete_object(object)
  end

  defp create_table(record) do
    :mnesia.create_table record, [{:attributes, Dict.keys(record.__record__(:fields))}]
  end
end

# start the database
:mnesia.start

# create the User table
Database.create_schema

# insert records
{:atomic, :ok} = :mnesia.transaction fn ->
  Database.write(User.new(email: "jsmith1@home.com", first: "John", last: "Smith"))
  Database.write(User.new(email: "jsmith2@home.com", first: "Jane", last: "Smith"))
end

# read a record by key
{:atomic, user} = :mnesia.transaction fn ->
  Database.find(User, "jsmith1@home.com") 
end

IO.puts("Found user #{inspect user}")

# delete the user
:mnesia.transaction fn ->
  Database.delete(user)
end

# query with qlc. finds all users with last name == "Smith"
{:atomic, users} = :mnesia.transaction fn ->
  query = :qlc.q(lc u inlist :mnesia.table(User), u.last == "Smith", do: u)

  :qlc.e(query)
end

IO.puts("Found results #{inspect users}")