In my opinion the best way to solve issues like this is to first decide how you would represent it in the database if you weren’t using Ecto. Keep in mind Ecto is just defining a mapping between Elixir and your persistence layer. If you don’t know what you want to do in your persistence layer you don’t know what you want to do in Ecto.

I would go for two maps handled by a homemade Ecto.Type:

• key => value
• key => index

When you want to access the key/value pairs in order, just use the second map.

Those two maps can also be wrapped in a single map, no need for two DB table columns either.

iex(1)> kv = [%{a: 12}, %{b: 102}, %{c: 9}]
[%{a: 12}, %{b: 102}, %{c: 9}]
iex(2)> Enum.find_value(kv, fn kv -> kv[:b] end)
102