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weighted_counter_updates

⚖️ Weighted Counter Updates with delta_magnitude​

By default, CounterCulture adds or subtracts one per record change. For scenarios where you need to sum a numeric field (e.g., quantity or price), use the delta_magnitude option. This computes the delta dynamically on create, update, and destroy actions.

# app/models/line_item.rb
class LineItem < ApplicationRecord
  belongs_to :order

  # Instead of +1, add the quantity of each line item to order.items_count
  counter_culture :order,
    column_name: 'items_count',
    delta_magnitude: ->(line_item) { line_item.quantity }
end

# Run backfill to correct existing orders
LineItem.counter_culture_fix_counts

Here, whenever a LineItem is created, updated, or destroyed, the order.items_count will change by the line item's quantity, accurately reflecting total items rather than just record count.