Allows caching of delegated attributes.
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README.md

DelegateCached

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Overview

delegate_cached allows you to cache delegated attributes on the delegating model and provides options to update the cached values when changed on the delegated-to model.

Installation

Add this line to your application's Gemfile:

gem 'delegate_cached'

And then execute:

$ bundle

Or install it yourself as:

$ gem install delegate_cached

Usage

We'll be caching the delegated attribute value, so your delegating ActiveRecord model will need a column to store the value. The column name will need to match the delegated attribute, or if using the prefix: true option, match the delegated attribute preceded by the to: option and _. For example, as below, the column names required would be hiker_name for the first delegate_cached definition, and name for the second. Create and run a migration for your new column/s unless they already exist.

class ThruHike < ApplicationRecord
  belongs_to :hiker, inverse_of: :thru_hikes
  belongs_to :trail, inverse_of: :thru_hikes

  delegate_cached :name, to: :hiker, prefix: true # 'hiker_name' column required on thru_hikes table
  delegate_cached :name, to: :trail               # 'name' column required on thru_hikes tables
end

Now, add your delegate_cached definition as in the example above. Note - you may only use delegate_cached on belongs_to and has_one associations.

This adds several methods to the delegating and delegated-to models.

class ThruHike < ApplicationRecord
  belongs_to :hiker, inverse_of: :thru_hikes
  belongs_to :trail, inverse_of: :thru_hikes

  delegate_cached :name, to: :hiker, prefix: true # 'hiker_name' column required on thru_hikes table
  delegate_cached :name, to: :trail               # 'name' column required on thru_hikes tables

  # This callback added by delegate_cached
  before_save :set_delegate_cached_value_for_hiker_name

  # This method added by delegate_cached
  def set_delegate_cached_value_for_hiker_name
    return unless hiker
    self['hiker_name'] = hiker.name
  end

  # This method added by delegate_cached
  def update_delegate_cached_value_for_hiker_name
    update(hiker_name: hiker.name)
  end

  # This method added by delegate_cached and overrides the ActiveRecord accessor
  # Cached value is returned unless nil. When nil, update the value from the
  # delegated_to model. To disable updating, use the update_when_nil = false option
  def hiker_name
    unless self['hiker_name'].nil?
      return self['hiker_name']
    end
    update_delegate_cached_value_for_hiker_name
    hiker.name
  end
end
class Hiker < ApplicationRecord
  has_many :thru_hikes, inverse_of: :hiker

  # This callback added by delegate_cached
  # To disable the callback, use the skip_callback = true option
  after_save :update_delegate_cached_value_for_thru_hikes_hiker_name, if: :name_changed?

  # This method added by delegate_cached
  def update_delegate_cached_value_for_thru_hikes_hiker_name
    ThruHike.where(hiker_id: id)
            .update_all(hiker_name: name)
  end
end
class Trail < ApplicationRecord
  has_many :thru_hikes, inverse_of: :trail

  # This callback added by delegate_cached
  # To disable the callback, use the skip_callback = true option
  after_save :update_delegate_cached_value_for_thru_hikes_name, if: :name_changed?

  # This method added by delegate_cached
  def update_delegate_cached_value_for_thru_hikes_name
    ThruHike.where(hiker_id: id)
            .update_all(name: name)
  end
end

Finally, use your models as you typically would with delegate When an instance of the delegated-to model is saved, a callback will update your delegate_cached value.

Options

to: X Required. Must be a belongs_to or has_one ActiveRecord association

prefix: true False by default. Changes the accessor name from accessor to to_accessor

inverse_of Tells delegate_cached the inverse_of for the to association when it is not defined on the association itself.

update_when_nil: true False by default. When set to true and the referenced attribute is called, if the existing cached value is nil, it will attempt to update the attribute value with the delegated value.

skip_callback: true False by default. When set to true, the after_save callback on the delegated-to model will not set.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/cselmer/delegate_cached. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests.

License

Copyright (c) 2016 Chris Selmer. The gem is available as open source under the terms of the MIT License.