Remove N+1 query for author in issues API

This was being masked by the statement cache because only one author was used
per issue in the test..

Also adds support for an Rspec matcher `exceed_all_query_limit`.

changelogs/unreleased/sh-add-uncached-query-limiter.yml

@@ -0,0 +1,5 @@
+---
+title: Remove N+1 query for author in issues API
+merge_request:
+author:
+type: performance

doc/development/query_recorder.md

@@ -22,6 +22,19 @@ As an example you might create 5 issues in between counts, which would cause the
 
 > **Note:** In some cases the query count might change slightly between runs for unrelated reasons. In this case you might need to test `exceed_query_limit(control_count + acceptable_change)`, but this should be avoided if possible.
 
+## Cached queries
+
+By default, QueryRecorder will ignore cached queries in the count. However, it may be better to count
+all queries to avoid introducing an N+1 query that may be masked by the statement cache. To do this,
+pass the `skip_cached` variable to `QueryRecorder` and use the `exceed_all_query_limit` matcher:
+
+it "avoids N+1 database queries" do
+  control_count = ActiveRecord::QueryRecorder.new(skip_cached: false) { visit_some_page }.count
+  create_list(:issue, 5)
+  expect { visit_some_page }.not_to exceed_all_query_limit(control_count)
+end
+```
+
 ## Finding the source of the query
 
 It may be useful to identify the source of the queries by looking at the call backtrace.

lib/api/issues.rb

@@ -16,7 +16,7 @@ module API
         args[:scope] = args[:scope].underscore if args[:scope]
 
         issues = IssuesFinder.new(current_user, args).execute
-          .preload(:assignees, :labels, :notes, :timelogs, :project)
+          .preload(:assignees, :labels, :notes, :timelogs, :project, :author)
 
         issues.reorder(args[:order_by] => args[:sort])
       end

spec/requests/api/issues_spec.rb

@@ -630,15 +630,17 @@ describe API::Issues do
     end
 
     it 'avoids N+1 queries' do
-      control_count = ActiveRecord::QueryRecorder.new do
+      get api("/projects/#{project.id}/issues", user)
+
+      control_count = ActiveRecord::QueryRecorder.new(skip_cached: false) do
         get api("/projects/#{project.id}/issues", user)
       end.count
 
-      create(:issue, author: user, project: project)
+      create_list(:issue, 3, project: project)
 
       expect do
         get api("/projects/#{project.id}/issues", user)
-      end.not_to exceed_query_limit(control_count)
+      end.not_to exceed_all_query_limit(control_count)
     end
 
     it 'returns 404 when project does not exist' do

spec/support/helpers/query_recorder.rb

@@ -1,10 +1,11 @@
 module ActiveRecord
   class QueryRecorder
-    attr_reader :log, :cached
+    attr_reader :log, :skip_cached, :cached
 
-    def initialize(&block)
+    def initialize(skip_cached: true, &block)
       @log = []
       @cached = []
+      @skip_cached = skip_cached
       ActiveSupport::Notifications.subscribed(method(:callback), 'sql.active_record', &block)
     end
 
@@ -16,7 +17,7 @@ module ActiveRecord
     def callback(name, start, finish, message_id, values)
       show_backtrace(values) if ENV['QUERY_RECORDER_DEBUG']
 
-      if values[:name]&.include?("CACHE")
+      if values[:name]&.include?("CACHE") && skip_cached
         @cached << values[:sql]
       elsif !values[:name]&.include?("SCHEMA")
         @log << values[:sql]

spec/support/matchers/exceed_query_limit.rb

@@ -1,17 +1,4 @@
-RSpec::Matchers.define :exceed_query_limit do |expected|
-  supports_block_expectations
-
-  match do |block|
-    @subject_block = block
-    actual_count > expected_count + threshold
-  end
-
-  failure_message_when_negated do |actual|
-    threshold_message = threshold > 0 ? " (+#{@threshold})" : ''
-    counts = "#{expected_count}#{threshold_message}"
-    "Expected a maximum of #{counts} queries, got #{actual_count}:\n\n#{log_message}"
-  end
-
+module ExceedQueryLimitHelpers
   def with_threshold(threshold)
     @threshold = threshold
     self
@@ -43,7 +30,7 @@ RSpec::Matchers.define :exceed_query_limit do |expected|
   end
 
   def recorder
-    @recorder ||= ActiveRecord::QueryRecorder.new(&@subject_block)
+    @recorder ||= ActiveRecord::QueryRecorder.new(skip_cached: skip_cached, &@subject_block)
   end
 
   def count_queries(queries)
@@ -61,4 +48,52 @@ RSpec::Matchers.define :exceed_query_limit do |expected|
       @recorder.log_message
     end
   end
+
+  def skip_cached
+    true
+  end
+
+  def verify_count(&block)
+    @subject_block = block
+    actual_count > expected_count + threshold
+  end
+
+  def failure_message
+    threshold_message = threshold > 0 ? " (+#{@threshold})" : ''
+    counts = "#{expected_count}#{threshold_message}"
+    "Expected a maximum of #{counts} queries, got #{actual_count}:\n\n#{log_message}"
+  end
+end
+
+RSpec::Matchers.define :exceed_all_query_limit do |expected|
+  supports_block_expectations
+
+  include ExceedQueryLimitHelpers
+
+  match do |block|
+    verify_count(&block)
+  end
+
+  failure_message_when_negated do |actual|
+    failure_message
+  end
+
+  def skip_cached
+    false
+  end
+end
+
+# Excludes cached methods from the query count
+RSpec::Matchers.define :exceed_query_limit do |expected|
+  supports_block_expectations
+
+  include ExceedQueryLimitHelpers
+
+  match do |block|
+    verify_count(&block)
+  end
+
+  failure_message_when_negated do |actual|
+    failure_message
+  end
 end