DETS example

dets_test.exs

defmodule Server do
  use Bitwise

  require Record
  Record.defrecord :server, id: nil, ip: nil, username: nil, password: nil

  def from_id(id) do
    ip = "127.#{band(id >>> 16, 0xff)}.#{band(id >>> 8, 0xff)}.#{band(id, 0xff)}"
    server(id: id, ip: ip, username: "username_#{band(id, 0xff)}", password: "password")
  end
end

defmodule DetsTest do
  use ExUnit.Case
  require Server

  @count 1_000_000

  test "foo" do
    {:ok, db} = :dets.open_file(:foo_db, [{:auto_save, 1000}, {:keypos, Server.server(:id) + 1}, {:file, './foo_db.dets'}])

    # Insert records if the count is wrong
    if :dets.info(db)[:size] < @count do
      data = Enum.map(1..@count, &Server.from_id/1)
      :dets.insert(db, data)
    end

    # Output dets table info
    IO.inspect :dets.info(db)

    # Find server with ID=1234
    rec = :dets.lookup(db, 1234)

    IO.inspect rec

    # Find IDs of servers sharing username = "username_210"
    # Returns the array of IDs (notice the $1 saying the first field
    # should be in the first place of the resulting record)
    recs = :dets.match(db, {:server, :"$1", :_, "username_210", :_})

    IO.puts "Found #{length(recs)} records"
    IO.inspect recs

    # Find all records of servers sharing username = "username_210"
    # Returns the array of full records
    recs = :dets.match_object(db, {:server, :_, :_, "username_210", :_})

    # We turn tuples into Elixir records before display this time
    IO.puts "Found #{length(recs)} records"
    IO.inspect Enum.map(recs, &(Server.server(&1)))

    :dets.close(db)
  end
end