it lets you create beautiful sql like declarations
```
payment_types = from(s in Ecto.assoc(order_cycle, :splits))
|> join(:left, [s], p in assoc(s, :payments))
|> select([s, p], %{
type: p.type,
card_type: p.card_type
})
|> Repo.all()
```
its the first database library that makes queries easy to compose together. On top of that transactions are a snap to put together thanks to Ecto.Multi
