Are translated_fields really dynamic?
If no, then I’d recommend to use simpler select expression:
|> select([product: p, translation: t], %{p | name: coalesce(t.name, p.name)})
actually, multiple select_merge can be composed:
translated_fields
|> Enum.reduce(query, fn
# it would be great to have something like this:
# field, query ->
# query |> select_merge([product: p, translation:t], %{^field => coalesce(field(t, ^field), field(p, ^field))})
# but dynamic atoms are not supported as a field key
:name, query ->
query
|> select_merge([product: p, translation: t], %{name: coalesce(t.name, p.name)})
:description, query ->
query
|> select_merge([product: p, translation: t], %{description: coalesce(t.description, p.description)})
end)
