An Ecto.Type storing an Elixir Duration.t/0 in a PostgreSQL interval column.

Elixir's Duration is an amount of time in calendar units, which is exactly what the PostgreSQL interval type stores. Storing a duration as an interval rather than a number of seconds keeps its calendar meaning — "one month" is a month, not thirty days — and lets the database add it to a date or sum a column of them.

For the localized Localize.Duration.t/0 struct, see Localize.Duration.Ecto.Type.

Schema

# in a migration
add :retention, :interval

# in a schema
field :retention, Localize.Ecto.Type.Duration

Normalization

PostgreSQL interval keeps three components — months, days and time — so units within a component are interchangeable: ninety minutes loads back as one hour and thirty minutes, and a week loads back as seven days (interval has no separate week). The month and day components are kept distinct, because PostgreSQL applies them separately when an interval is added to a date. A duration already in this normal form round-trips unchanged.