create_user!(user_params) and create_email!(user, email_params) would need to return {:ok, resource} or {:error, reason}, so these are unlikely to be “bang” operations.

And the last |> Repo.insert() would need to be replaced with Repo.transaction().

@fireproofsocks note that Multi.runs are not automatically rolled back on errors, I’d probably use inserts instead. Modifying @abitdodgy’s example:

alias Ecto.Multi

Multi.new()
|> Multi.insert(:user, User.changeset(%User{}, user_params) end)
|> Multi.insert(:email, fn %{user: %User{id: user_id}} ->
  Email.changeset(%Email{author_id: user_id}, email_params)
end)
|> Repo.transaction()

Edit: I’d use @idi527’s example as it’s much more idiomatic.

Here’s a contrived example that should give you the general idea.

Ecto.Multi.new
|> Ecto.Multi.run(:user, fn _ ->
  create_user(user_params)
end)
|> Ecto.Multi.run(:email, fn %{user: user} ->
  create_email(user, email_params)
end)
|> Repo.transaction()

When you use Multi.run, you tag the operation using the second argument. For example, the |> Ecto.Multi.run(:user ... makes the result of create_user available under the :user key in the next the function.

Are you sure? A Multi is executed in a transaction and for as long as the command in a Multi.run does only cause side effects to the db and nothing else it should just be rolled back like any other db operation, which happened in that transaction. I‘ve even some places in my projects, where Multis are effectively nested, as the inner multis are executed in named functions which a outer multi composes.

Precisely, DB actions are rolled back because of a transaction, but run/3,5 is often used to perform non-db actions that need to be run only if the DB succeeds, however there is not version of run/? that allows you to pass both a ‘do’ and an ‘undo’ function, which would be a huge help personally. as right now you have to check it ‘after’ running Repo.transaction, thus meaning the actions of the multi have to ‘leak’ out of where they are defined. We could really use a run/4;8 as well to support both a do and undo…