Ecto Multi in a Loop

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To answer your question “how do I use Ecto.Multi in a loop”, you would use Enum.reduce/3 to build up the Multi as you process elements in an enumerable.

def parse(_) do
  multi = Ecto.Multi.new()

  multi = 
    File.stream!("uploads/#{file}", [:trim_bom])
    |> CSV.decode(headers: true)
    |> Enum.reduce(multi, &process_row/2)
  
  Repo.transaction(multi)
end

defp process_row(row, multi) do
  parsed_row = ...

  Ecto.Multi.insert(multi, ...)
end
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