Kalecto

Glue between Kalends and Ecto. For saving dates, times and datetimes in Ecto.

defp deps do
      [ {:kalecto, "~> 0.3.0"}, ]
    end

Super quick way to get started

Here’s how to display inserted_at and updated_at dates using the functionality of the Kalends library:

• Add :kalecto to your deps in your mix.exs file (see above) and run mix deps.get
• In your Ecto models, where you have a schema definition with a timestamps line, under the line that says use Ecto.Model add use Kalecto.Model like so:

defmodule Weather do
  use Ecto.Model
  use Kalecto.Model

  schema "weather" do
    field :city, :string
    timestamps
  end
end

This means that your timestamps will be loaded as Kalends.DateTime structs instead of Ecto.DateTime structs and you can use the formatting functionality in Kalends.

• Format an inserted_at timestamp using Kalends:

@post.inserted_at |> Kalends.DateTime.Format.strftime!("%A, %e %B %Y")

It will return for instance: Monday, 9 March 2015

There are other formatting functions. For instance: http timestamp, unix timestamp, RFC 3339 (ISO 8601). You can also shift the timestamp to another timezone in order to display what date and time it was in that particular timezone. See more in the Kalends documentation.

The types

If you have a primitive type as listed below you can swap it for a Kalecto type simply by adding the type to your Ecto schema.

If you have a datetime as a primitive type, you can use NaiveDateTime or DateTimeUTC. If you have a date as a primitive type, you can use Kalecto.Date. If you have a time as a primitive type, you can use Kalecto.Time.

Put the primitive type in your migrations and the Ecto type in your schema.

*) If you are using Postgres as a database you can also use the Kalecto.DateTime type. This allows you to save any Kalends.DateTime struct. This is useful for saving for instance future times for meetings in a certain timezone. Even if timezone rules change, the “wall time” will stay the same. See the “DateTime with Postgres” heading below.

Example usage

In your Ecto schema:

defmodule Weather do
  use Ecto.Model
  use Kalecto.Model

  schema "weather" do
    field :temperature,      :integer
    field :nice_date,        Kalecto.Date
    field :nice_time,        Kalecto.Time
    field :nice_datetime,    Kalecto.DateTimeUTC
    field :another_datetime, Kalecto.NaiveDateTime
    timestamps usec: true
    # the timestamps will be DateTimeUTC because of the `use Kalecto.Model` line
  end
end

If you have a Kalends DateTime in the Etc/UTC timezone you can save it in Ecto as a DateTimeUTC.

Let’s create a new DateTime to represent “now”:

iex> example_to_be_saved_in_db = Kalends.DateTime.now_utc
    %Kalends.DateTime{abbr: "UTC", day: 2, hour: 16, usec: 245828, min: 48,
     month: 3, sec: 19, std_off: 0, timezone: "Etc/UTC", utc_off: 0, year: 2015}

Another way of getting a DateTime is parsing JavaScript style milliseconds:

iex> parsed_datetime = Kalends.DateTime.Parse.js_ms!("1425314899000")
    %Kalends.DateTime{abbr: "UTC", day: 2, hour: 16, usec: 0, min: 48, month: 3,
     sec: 19, std_off: 0, timezone: "Etc/UTC", utc_off: 0, year: 2015}

Since the field nice_datetime is of the DateTimeUTC type, we can save Kalends.DateTime structs there if they are in the Etc/UTC timezone:

weather_struct_to_be_saved = %Weather{nice_datetime: parsed_datetime}

When a Kalecto.DateTimeUTC type is received from the database it is loaded as a Kalends.DateTime struct. We can use the functions in Kalends to shift this UTC datetime to another time zone:

iex> example_loaded_from_db |> Kalends.DateTime.shift_zone!("Europe/Copenhagen")
    %Kalends.DateTime{abbr: "CET", day: 2, hour: 17, usec: nil, min: 48,
      month: 3, sec: 19, std_off: 0, timezone: "Europe/Copenhagen", utc_off: 3600,
      year: 2015}

Or we could get the unix timestamp:

iex> example_loaded_from_db |> Kalends.DateTime.Format.unix
    1425314899

Or format it via strftime:

iex> example_loaded_from_db |> Kalends.DateTime.Format.strftime!("The time is %T and it is %A.")
    "The time is 16:48:19 and it is Monday."

DateTime with Postgres

If you are using Postgres, you can save and load DateTime structs that are not in the Etc/UTC timezone. This requires that a special type is added to the database. By running the following command you can generate a migration that adds this type:

mix kalecto.add_type_migration

Then run the migration (mix ecto.migrate). This adds the kalends_datetime type to the Postgres database. In migrations you can use :kalends_datetime.

In the schemas you can use the type Kalecto.DateTime for fields that have been created with :kalends_datetime type in migrations.

Documentation

Documentation for Kalecto is available at hexdocs.

More information about Kalends functionality in the Kalends documentation.