add efficient index for quickly finding billable metrics with an expr…

…ession

app/models/billable_metric.rb

@@ -48,6 +48,8 @@ class BillableMetric < ApplicationRecord
 
   default_scope -> { kept }
 
+  scope :with_expression, -> { where("expression IS NOT NULL AND expression <> ''") }
+
   def self.ransackable_attributes(_auth_object = nil)
     %w[name code]
   end
@@ -108,6 +110,7 @@ def validate_expression
 # Indexes
 #
 #  index_billable_metrics_on_deleted_at                (deleted_at)
+#  index_billable_metrics_on_org_id_and_code_and_expr  (organization_id,code,expression) WHERE ((expression IS NOT NULL) AND ((expression)::text <> ''::text))
 #  index_billable_metrics_on_organization_id           (organization_id)
 #  index_billable_metrics_on_organization_id_and_code  (organization_id,code) UNIQUE WHERE (deleted_at IS NULL)
 #

app/services/events/create_service.rb

@@ -42,12 +42,9 @@ def call
     attr_reader :organization, :params, :timestamp, :metadata
 
     def pre_ingest(event)
-      # TODO: make this efficient
-      bm = organization.billable_metrics.find_by(code: event.code)
+      bm = organization.billable_metrics.with_expression.find_by(code: event.code)
       return unless bm
 
-      return if bm.expression.blank?
-
       evaluation_event = Lago::Event.new(event.code, event.timestamp.to_i, event.properties)
 
       value = Lago::ExpressionParser.parse(bm.expression)&.evaluate(evaluation_event)

db/migrate/20241018112637_add_expression_index_to_billable_metrics.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class AddExpressionIndexToBillableMetrics < ActiveRecord::Migration[7.1]
+  disable_ddl_transaction!
+  def change
+    add_index :billable_metrics, [:organization_id, :code, :expression],
+      name: 'index_billable_metrics_on_org_id_and_code_and_expr',
+      algorithm: :concurrently,
+      where: "expression IS NOT NULL AND expression <> ''"
+  end
+end