Convert Map to JSON when saving to database?

If you’re using postgres I’d recommend storing the field as jsonb in the database instead of a string, then if you have a field :metadata, :map ecto will handle the serialization for you (and you can even query and index directly on fields inside the jsonb column)

Just to be thorough for future visitors, here’s the full example:

From my migration:

# ...
# (The :map type gets mapped to :jsonb for PostGres from what I understand)
add :meta, :map, default: "{}"  # <-- assuming I always want to store a JSON object

From my schema:

# ...
field :meta, :map, null: false, default: "{}"

And how it all works:

attrs = %{
    # ...
    meta: %{
        arbitrary: "stuff"
    }
}
result = %MyThing{}
  |> MyThing.changeset(attrs)
  |> Repo.insert()

  # result:
  %Auth.Schemas.AuthorityUser{
      __meta__: #Ecto.Schema.Metadata<:loaded,"my_thing">,
      # ...
      meta: %{
          "arbitrary" => "stuff",
      },
     # ...
  }

I believe that in your migration file(s) and schema module(s) you can replace the "{}" string literal with a map literal: %{}.