Measured Rails

This gem is the Rails integration for the measured gem.

It provides ActiveRecord adapter for persisting and retrieving measurements with their units, and model validations.

Installation

Using bundler, add to the Gemfile:

gem 'measured-rails'

Or stand alone:

$ gem install measured-rails

Usage

ActiveRecord

Columns are expected to have the _value and _unit suffix, and be DECIMAL and VARCHAR, and defaults are accepted. Customizing the column used to hold units is supported, see below for details.

class AddWeightAndLengthToThings < ActiveRecord::Migration
  def change
    add_column :things, :minimum_weight_value, :decimal, precision: 10, scale: 2
    add_column :things, :minimum_weight_unit, :string, limit: 12

    add_column :things, :total_length_value, :decimal, precision: 10, scale: 2, default: 0
    add_column :things, :total_length_unit, :string, limit: 12, default: "cm"
  end
end

A column can be declared as a measurement with its measurement subclass:

class Thing < ActiveRecord::Base
  measured Measured::Weight, :minimum_weight
  measured Measured::Length, :total_length
end

You can optionally customize the model's unit column by specifying it in the unit_field_name option, as follows:

class ThingWithCustomUnitAccessor < ActiveRecord::Base
  measured_length :length, :width, :height,     unit_field_name: :size_unit
  measured_weight :total_weight, :extra_weight, unit_field_name: :weight_unit
end

There are some simpler methods for predefined types:

class Thing < ActiveRecord::Base
  measured_weight :minimum_weight
  measured_length :total_length
end

This will allow you to access and assign a measurement object:

thing = Thing.new
thing.minimum_weight = Measured::Weight.new(10, "g")
thing.minimum_weight_unit     # "g"
thing.minimum_weight_value    # 10

Order of assignment does not matter, and each property can be assigned separately and with mass assignment:

params = { total_length_unit: "cm", total_length_value: "3" }
thing = Thing.new(params)
thing.total_length.to_s   # 3 cm

Validations

Validations are available:

class Thing < ActiveRecord::Base
  measured_length :total_length

  validates :total_length, measured: true
end

This will validate that the unit is defined on the measurement, and that there is a value.

Rather than true the validation can accept a hash with the following options:

message: Override the default "is invalid" message.
units: A subset of units available for this measurement. Units must be in existing measurement.
greater_than
greater_than_or_equal_to
equal_to
less_than
less_than_or_equal_to

All comparison validations require Measured::Measurable values, not scalars. Most of these options replace the numericality validator which compares the measurement/method name/proc to the column's value. Validations can also be combined with presence validator.

Note: Validations are strongly recommended since assigning an invalid unit will cause the measurement to return nil, even if there is a value:

thing = Thing.new
thing.total_length_value = 1
thing.total_length_unit = "invalid"
thing.total_length  # nil

Tests

$ bundle exec rake test

Contributing

Fork it ( https://github.com/Shopify/measured-rails/fork )
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create a new Pull Request

railsmechanic/measured-rails