^value in table.array query leads to an exception

[ontofractal]

in operator doesn't work as expected in the following code:

tag = "elixir"
query = from p in Post, where: ^tag in p.tags, order_by: [desc: p.id]
posts = Repo.all(query)

When run process is terminated with the following exception:

** (exit) an exception was raised:
    ** (Protocol.UndefinedError) protocol Enumerable not implemented for {{:., [], [{:&, [], [0]}, :tags]}, [], []}
        (elixir) lib/enum.ex:1: Enumerable.impl_for!/1
        (elixir) lib/enum.ex:116: Enumerable.reduce/3
        (elixir) lib/enum.ex:1776: Enum.map/2
        (ecto_mnesia) lib/ecto_mnesia/record/context/match_spec.ex:89: Ecto.Mnesia.Record.Context.MatchSpec.condition_expression/3
        (ecto_mnesia) lib/ecto_mnesia/record/context/match_spec.ex:63: Ecto.Mnesia.Record.Context.MatchSpec.match_conditions/4
        (ecto_mnesia) lib/ecto_mnesia/record/context/match_spec.ex:19: Ecto.Mnesia.Record.Context.MatchSpec.update/2
        (ecto_mnesia) lib/ecto_mnesia/adapter.ex:58: Ecto.Mnesia.Adapter.execute/6
        (ecto) lib/ecto/repo/queryable.ex:130: Ecto.Repo.Queryable.execute/5
        (ecto) lib/ecto/repo/queryable.ex:35: Ecto.Repo.Queryable.all/4
...
...

relevant schema part is

field :tags, {:array, :string}

Any advice? Thanks!

[AndrewDryga]

Hello.

Unfortunately this adapter uses MatchSpec to query fields, and there is no easy way to make "item in field value" queries. I guess it can be done by using QLC instead of MatchSpec, but we are not at that point yet.

I will add a raise for this case, to make it clear for developers.

P.S.: Even :in is emulated by replacing it with multiple :or statements.