Custom Ecto Type Questions

tielur · August 3, 2018, 5:16am

I’m currently facing a common problem that I believe is refered to as the EAV model in database modeling. Where I am going to be storing answers to questions. Those answers could be many different types, everything from booleans(Yes / No), Strings, Numbers, Dates, ect…

I had a thought, and I’m not sure if it’s even possible and or if it would be a terrible idea. Or…maybe there’s a better way to do this?

But would it be possible to write a custom ecto type using the Ecto.Type behavior that would store the answer value along side the answer datatype. So that I can use one column to store the answer and then still have types when I read it back into Elixir?

I’ve also been exploring JSONB.

LostKobrakai · August 3, 2018, 5:51am

ex_money is using a single column to store amount and currency. Maybe look at how it handles that.

tielur · August 3, 2018, 6:02am

Ahh thanks, yea it looks like they are using a custom ecto type as well:

github.com

kipcole9/money/blob/fd2668b61898f1ec9ff0d21e2d9b597e641296b0/lib/money/ecto/money_ecto_map_type.ex

if Code.ensure_loaded?(Ecto.Type) do
  defmodule Money.Ecto.Map.Type do
    @moduledoc """
    Implements Ecto.Type behaviour for Money, where the underlying schema type
    is a map.

    This is the required option for databases such as MySQL that do not support
    composite types.

    In order to preserve precision, the amount is serialized as a string since the
    JSON representation of a numeric value is either an integer or a float.

    `Decimal.to_string/1` is not guaranteed to produce a string that will round-trip
    convert back to the identical number.  However given enough precision in the
    `Decimal.get_context/0` then round trip conversion should be expected.  The default
    precision in the context is 28 digits.
    """

    @behaviour Ecto.Type

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tielur · August 3, 2018, 6:04am

I guess there’s a thing called composite types in Postgresql that it uses as well. Interesting…