How to persist data in functional Elixir

and where you want to persit the data? You have a few options:

1. Relational database. Most obvious / popular choice is to use Ecto GitHub - elixir-ecto/ecto: A toolkit for data mapping and language integrated query. · GitHub
2. Serialize to binary blob with :erlang.term_to_binary/1 and save to file
3. Use DETS dets — OTP 29.0.2 (stdlib 8.0.1)
4. Use Mnesia (via Amnesia or directly, GitHub - meh/amnesia: Mnesia wrapper for Elixir. · GitHub)
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5. There are many many many more options.

There are 2 different meanings to this:

First is to really persist the data even when the application restarts

• This is well explained in the above post from @hubertlepicki

Second is to keep data only in running application [keep a state] (like an object instance in OO languages)

• Manual state struct which you’ll pass around in the module
  • I use this option if I need to keep just a simple state in one module
• You can use Agents: http://elixir-lang.github.io/getting-started/mix-otp/agent.html
  • I use this if I need to keep state between more modules
• You can create a GenServer: GenServer — Elixir v1.20.2
  • a bit more robust solution.

The above state won’t survive the application crashes/restarts though, so you usually use the mix of GenServer/Agent and Database/Amnesia/DETS, etc.

This is a great article that talks about the different states , it is for Erlang, but it explains theory well.

Cheers mate