Implement instantiation.active_record subscriber

Partially address #74

CHANGELOG.md

@@ -9,6 +9,7 @@ For the full commit log, [see here](https://github.com/influxdata/influxdb-rails
 - Drop undocumented `instrumentation_enabled` setting, use
   `ignored_environments` do disable instrumentation
 - Simplified spec with a PORO test client
+- Implement `instantiation.active_record` subscriber (https://guides.rubyonrails.org/active_support_instrumentation.html#instantiation-active-record)
 
 ## v1.0.0, released 2019-10-23
 The Final release, no code changes.

lib/influxdb-rails.rb

@@ -5,6 +5,7 @@
 require "influxdb/rails/middleware/render_subscriber"
 require "influxdb/rails/middleware/request_subscriber"
 require "influxdb/rails/middleware/sql_subscriber"
+require "influxdb/rails/middleware/active_record_subscriber"
 require "influxdb/rails/sql/query"
 require "influxdb/rails/version"
 require "influxdb/rails/configuration"

lib/influxdb/rails/middleware/active_record_subscriber.rb

@@ -0,0 +1,26 @@
+require "influxdb/rails/middleware/subscriber"
+require "influxdb/rails/sql/query"
+
+module InfluxDB
+  module Rails
+    module Middleware
+      class ActiveRecordSubscriber < Subscriber # :nodoc:
+        private
+
+        def values(started, finished, payload)
+          {
+            value:        ((finished - started) * 1000).ceil,
+            record_count: payload[:record_count],
+          }
+        end
+
+        def tags(payload)
+          {
+            hook:       "instantiation",
+            class_name: payload[:class_name],
+          }
+        end
+      end
+    end
+  end
+end

lib/influxdb/rails/railtie.rb

@@ -29,6 +29,7 @@ class Railtie < ::Rails::Railtie # :nodoc:
           "render_partial.action_view"       => Middleware::RenderSubscriber,
           "render_collection.action_view"    => Middleware::RenderSubscriber,
           "sql.active_record"                => Middleware::SqlSubscriber,
+          "instantiation.active_record"      => Middleware::ActiveRecordSubscriber,
         }.each do |hook_name, subscriber_class|
           subscribe_to(hook_name, subscriber_class)
         end

spec/requests/active_record_instantiation_metrics_spec.rb

@@ -0,0 +1,65 @@
+require File.dirname(__FILE__) + "/../spec_helper"
+
+RSpec.describe "ActiveRecord instantiation metrics", type: :request do
+  let(:tags_middleware) do
+    lambda do |tags|
+      tags.merge(tags_middleware: :tags_middleware)
+    end
+  end
+  let(:metric) { Metric.create!(name: "name") }
+  before do
+    allow_any_instance_of(InfluxDB::Rails::Configuration).to receive(:ignored_environments).and_return(%w[development])
+    allow_any_instance_of(ActionDispatch::Request).to receive(:request_id).and_return(:request_id)
+    allow_any_instance_of(InfluxDB::Rails::Configuration).to receive(:application_name).and_return(:app_name)
+    allow_any_instance_of(InfluxDB::Rails::Configuration).to receive(:tags_middleware).and_return(tags_middleware)
+  end
+
+  it "writes metric" do
+    get metric_path(metric)
+
+    expect_metric(
+      tags:   a_hash_including(
+        location:        "MetricsController#show",
+        hook:            "instantiation",
+        class_name:      "Metric",
+        additional_tag:  :value,
+        server:          Socket.gethostname,
+        app_name:        :app_name,
+        tags_middleware: :tags_middleware
+      ),
+      values: a_hash_including(
+        additional_value: :value,
+        request_id:       :request_id,
+        value:            be_between(1, 30),
+        record_count:     1
+      )
+    )
+  end
+
+  it "includes correct timestamps" do
+    travel_to Time.zone.local(2018, 1, 1, 9, 0, 0)
+
+    get metric_path(metric)
+
+    expect_metric(
+      tags:      a_hash_including(
+        location: "MetricsController#show",
+        hook:     "instantiation"
+      ),
+      timestamp: 1_514_797_200
+    )
+  end
+
+  it "does not write metric when hook is ignored" do
+    allow_any_instance_of(InfluxDB::Rails::Configuration).to receive(:ignored_hooks).and_return(["instantiation.active_record"])
+
+    get metric_path(metric)
+
+    expect_no_metric(
+      tags: a_hash_including(
+        location: "MetricsController#show",
+        hook:     "instantiation"
+      )
+    )
+  end
+end

spec/support/rails4/app.rb

@@ -12,7 +12,7 @@
 app.initialize!
 
 app.routes.draw do
-  resources :metrics, only: :index
+  resources :metrics, only: %i[index show]
   resources :exceptions, only: :index
 end
 
@@ -41,6 +41,10 @@ class MetricsController < ApplicationController
   def index
     Metric.create!(name: "name")
   end
+
+  def show
+    @metric = Metric.find_by(name: "name")
+  end
 end
 
 class ExceptionsController < ApplicationController

spec/support/rails5/app.rb

@@ -12,7 +12,7 @@
 app.initialize!
 
 app.routes.draw do
-  resources :metrics, only: :index
+  resources :metrics, only: %i[index show]
   resources :exceptions, only: :index
 end
 
@@ -41,6 +41,10 @@ class MetricsController < ApplicationController
   def index
     Metric.create!(name: "name")
   end
+
+  def show
+    @metric = Metric.find_by(name: "name")
+  end
 end
 
 class ExceptionsController < ApplicationController

spec/support/rails6/app.rb

@@ -12,7 +12,7 @@
 app.initialize!
 
 app.routes.draw do
-  resources :metrics, only: :index
+  resources :metrics, only: %i[index show]
   resources :exceptions, only: :index
 end
 
@@ -41,6 +41,10 @@ class MetricsController < ApplicationController
   def index
     Metric.create!(name: "name")
   end
+
+  def show
+    @metric = Metric.find_by(name: "name")
+  end
 end
 
 class ExceptionsController < ApplicationController

spec/support/views/metrics/show.html.erb

@@ -0,0 +1,4 @@
+<h1>Show</h1>
+<div>
+  <%= @metric.name %>
+</div>