Rails using enum type as a value for an attribute

Question

Here is my model defination:

class OrderFrequency < ApplicationRecord
  self.table_name = "order_frequencies"
  enum frequency_unit: { hour: 1}

end

and migration

class CreateOrderFrequencies < ActiveRecord::Migration[5.2]
  def change
    create_table :order_frequencies do |t|
      t.string :value
      t.integer :unit
      t.timestamps
    end
  end
end

So how do I assign unit attribute with enum of frequency_unit?

I cannot do

OrderFrequency.create(value: 'value 123', unit: OrderFrequency.frequency_unit.hour)

What is the correct way to use frequency_unit enum for the unit attribute?

Thanks

Tom Lord · Accepted Answer · 2019-10-10 08:23:12Z

1

See the official documentation for ActiveRecord::Enum -- the idea isn't to have two attribute names (unit and frequency_unit); you should only have one. (After all, it's the same thing!)

Let's change your model to:

class OrderFrequency < ApplicationRecord
  # Note: Specifying the (default) table_name here is also redundant
  enum unit: { hour: 1 }
end

Now you can create a record via:

OrderFrequency.create(
  value: 'value 123',
  unit: OrderFrequency.units['hour']
)

Or even (!!) by just writing:

OrderFrequency.create(
  value: 'value 123',
  unit: 'hour'
)

The key idea with ActiveRecord::Enum is that in the database the value is stored as an integer, but in the application (99% of the time) you can work with human-friendly Strings - i.e. "hour" rather than 1.

If for some reason you need to retrieve a list of all known units, you can do this with:

OrderFrequency.units.keys #=> ['hour']

edited Oct 10, 2019 at 8:23

answered Oct 10, 2019 at 8:13

Tom Lord

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