ColumnSync

Keeping in sync columns in different tables is a pretty common step during database refactorings. The column_sync gem provides ActiveRecord migration helpers to facilitate the sync of data between columns.

Installation

Install the gem and add to the application's Gemfile by executing:

$ bundle add column_sync

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install column_sync

Usage

The following snippet should be used as a migration template:

class SyncColumns < ActiveRecord::Migration[7.1]
  def up
    sync_columns(Subscription => :country_code, Company => :country)
  end

  def down
    unsync_columns(Subscription => :country_code, Company => :country)
  end
end

The migration above generates the functions and triggers needed to keep subscriptions.country_code in sync with companies.country.

You also need to update your models to reflect the syncroniaztion between their columns:

class Company < ApplicationRecord
  include ColumnSync::Model

  has_one :subscription

  sync_column :country, to: :subscription, column: :country_code
end

class Subscription < ApplicationRecord
  include ColumnSync::Model

  belongs_to :company

  sync_column :country_code, to: :company, column: :country
end

Example

Given the following scenario:

Company.create!(country: "es")
Subscription.create!(country_code: "es", company: Company.first)

Changes are reflected in memory when the value is modified:

company = Company.first
company.country = "fr"
company.subscription.country_code
# => "fr"

company.subscription.country_code = "ca"
company.country
# => "ca"

Changes are also reflected in the DB when the value is persisted:

company = Company.first
company.update(country: "it")
company.subscription.country_code
# => "it"

company.subscription.update(country_code: "ma")
company.country
# => "ma" 

Limitations

• Each sync_columns statement can only sync a pair of columns. If the same column needs to be synchronized across multiple tables, multiple such statements will be needed.
• The gem expects a has_one - belongs_to association between the models involved. It uses Rails reflections to understand the table names and column names involved.
• It is assumed that the records are initially in sync, so it does not automatically sync values using any of the two columns involved.
• It also does not sync values when a row is created, only when it is modified.