If anyone coming to this topic needs more tips on Ecto.Multi and transactions in general, we’ve written a post about it: How database transactions work in Ecto and why Elixir makes it awesome?

Yes, you can observe this with debug logging:

iex(5)> %Menu.Item{name: "Bar", price: 4.50, category: %Menu.Category{name: "Foo"}} |> Repo.insert!
[debug] QUERY OK db=0.3ms
begin []
[debug] QUERY OK db=6.6ms
INSERT INTO "categories" ("name","inserted_at","updated_at") VALUES ($1,$2,$3) RETURNING "id" ["Foo", {{2017, 11, 3}, {20, 21, 34, 814485}}, {{2017, 11, 3}, {20, 21, 34, 817077}}]
[debug] QUERY OK db=5.0ms
INSERT INTO "items" ("category_id","name","price","inserted_at","updated_at") VALUES ($1,$2,$3,$4,$5) RETURNING "id" [4, "Bar", #Decimal<4.5>, {{2017, 11, 3}, {20, 21, 34, 834005}}, {{2017, 11, 3}, {20, 21, 34, 834009}}]
[debug] QUERY OK db=0.8ms
commit []

Note the begin and commit lines. Those are the beginning and end of the transaction respectively.

You probably want an Ecto.Multi rather than using transactions directly as you get a bunch of extra stuff that you don’t get with Repo.transaction