How can I set "global" variables that can be accessed in controllers and models in Rails

Question

I have a table that has set entries. I would like to access those entries as variables in both my models and controllers without querying the database every time to set those variables.

I am able to get it to work by creating duplicate "concerns" for my models and controllers. I could also set global variables in my ApplicationController. Or i could initialize them in every place that I need them. What would be the correct rails way to set and access global variables that can be accessed in both controllers and models?

class ItemType
  has_many :items
end

class Item
  belongs_to :item_type
  belongs_to :foo
end

class Foo 
  has_many :items  

  def build_item
    bar_item_type = ItemType.find_by(:name => "bar")

    self.items.build(
      :foo_id => self.id,
      :item_type_id => bar_item_type.id
    )
  end
end

class ItemsController
  def update
    bar_item_type = ItemType.find_by(:name => "bar")

    @item.update(:item_type_id => bar_item_type.id)
  end

end

In the example, you can see that I am declaring the bar_item_type variable in both my Foo model and my ItemsController. I would like to DRY up my code base by being able to create and access that variable once for my rails project instead of having to make that same database call everywhere.

Answer 1

I would advocate against such hard-coded or DB state-dependent code. If you must do it, here's how one of the ways I know it can be done:

# models
class ItemType < ActiveRecord::Base
  has_many :items

  # caches the value after first call
  def self.with_bar
    @@with_bar ||= transaction { find_or_create_by(name: "bar") }
  end

  def self.with_bar_id
    with_bar.id
  end
end

class Item < ActiveRecord::Base
  belongs_to :item_type
  belongs_to :foo

  scope :with_bar_types, -> { where(item_type_id: ItemType.with_bar_id) }
end

class Foo < ActiveRecord::Base
  has_many :items  

  # automatically sets the foo_id, no need to mention explicitly
  # the chained with_bar_types automatically sets the item_type_id to ItemType.with_bar_id
  def build_item
    self.items.with_bar_types.new
  end
end

# Controller
class ItemsController
  def update
    @item.update(item_type_id: ItemType.with_bar_id)
  end
end