Idea for a fail-fast Rails initializer to check that database check constraints are in-sync with app code constants

validate_constraints.rb

# config/initializers/validate_constraints.rb
Rails.application.config.after_initialize do
  if Rails.env.development? || Rails.env.test?
    # Get the check constraint from the database schema
    connection = ActiveRecord::Base.connection
    constraint_sql = nil

    # Try to extract the constraint SQL
    begin
      # For PostgreSQL, you can query the information_schema
      result = connection.execute(<<~SQL)
        SELECT pg_get_constraintdef(oid) AS def
        FROM pg_constraint
        WHERE conname = 'reading_statuses_valid_status_check'
        AND conrelid = 'reading_statuses'::regclass;
      SQL

      constraint_sql = result.first["def"] if result.any?
    rescue => e
      Rails.logger.error("Failed to check constraints: #{e.message}")
    end

    if constraint_sql
      # Extract the values from the constraint SQL
      # This is a simplistic approach and may need adjustment based on exact SQL format
      db_values = constraint_sql.scan(/'([^']+)'/).flatten.sort

      # Get the values from the constants
      model_values = ReadingStatusConstants::VALID_STATUSES.sort

      # Compare the values
      unless db_values == model_values
        message = <<~MSG
          ERROR: Database constraint and model validation for ReadingStatus.status are out of sync!
          
          Database constraint values: #{db_values.inspect}
          Model validation values: #{model_values.inspect}
          
          This can lead to inconsistent behavior where the application accepts values that the database rejects.
          Please update the constraint or the model validation to ensure they are in sync.
        MSG

        Rails.logger.error(message)
        raise message if Rails.env.development? # Optional: crash in development
      end
    else
      Rails.logger.warn("Could not find reading_statuses_valid_status_check constraint")
    end
  end
end