Add spec for N+1

Author: tsugitta

spec/requests/graphql_spec.rb

@@ -0,0 +1,97 @@
+require 'rails_helper'
+
+RSpec.describe 'FragmentCache + Dataloader N+1 Investigation', type: :request do
+  before do
+    user1 = User.create!(name: "Alice")
+    user2 = User.create!(name: "Bob")
+    5.times do |i|
+      user1.posts.create!(title: "Alice Post #{i}")
+      user2.posts.create!(title: "Bob Post #{i}")
+    end
+  end
+
+  let(:query) do
+    <<~GRAPHQL
+      query($useCache: Boolean!) {
+        users {
+          id
+          name
+          posts(useCache: $useCache) {
+            id
+            title
+          }
+        }
+      }
+    GRAPHQL
+  end
+
+  context 'when cache_fragment is disabled' do
+    it 'should have minimal query count with effective batching' do
+      queries_count = 0
+      queries = []
+
+      counter = ->(_name, _started, _finished, _unique_id, payload) do
+        sql = payload[:sql].to_s
+        if sql.start_with?("SELECT")
+          queries_count += 1
+          queries << sql
+        end
+      end
+
+      ActiveSupport::Notifications.subscribed(counter, "sql.active_record") do
+        post '/graphql', params: {
+          query: query,
+          variables: { useCache: false }.to_json
+        }
+      end
+
+      puts "\n=== Queries without cache ==="
+      queries.each.with_index(1) do |sql, i|
+        puts "\n#{i}. #{sql}"
+      end
+
+      expect(response).to have_http_status(:success)
+      json_response = JSON.parse(response.body)
+      expect(json_response["errors"]).to be_nil
+      expect(json_response["data"]["users"]).to be_present
+      expect(queries_count).to be 2
+    end
+  end
+
+  context 'when cache_fragment is enabled' do
+    it 'should show increased query count due to N+1' do
+      GraphQL::FragmentCache.cache_store = ActiveSupport::Cache.lookup_store(:memory_store)
+
+      queries_count = 0
+      queries = []
+
+      counter = ->(_name, _started, _finished, _unique_id, payload) do
+        sql = payload[:sql].to_s
+        if sql.start_with?("SELECT")
+          queries_count += 1
+          queries << sql
+        end
+      end
+
+
+      ActiveSupport::Notifications.subscribed(counter, "sql.active_record") do
+        post '/graphql', params: {
+          query: query,
+          variables: { useCache: true }.to_json
+        }
+      end
+
+      puts "\n=== Queries with cache ==="
+      queries.each.with_index(1) do |sql, i|
+        puts "\n#{i}. #{sql}"
+      end
+
+
+      expect(response).to have_http_status(:success)
+      json_response = JSON.parse(response.body)
+      expect(json_response["errors"]).to be_nil
+      expect(json_response["data"]["users"]).to be_present
+      expect(queries_count).to be 3
+    end
+  end
+end