From 1f70f761f12b70a1550ab182e6308f67d5950571 Mon Sep 17 00:00:00 2001
From: Jens Kraemer <jk@jkraemer.net>
Date: Wed, 20 Mar 2019 18:08:03 +0800
Subject: [PATCH 1/2] introduces IssueQuery#lazy_issues

---
 app/models/issue_query.rb | 32 +++++++++++++++++++++++++++++---
 test/unit/query_test.rb   |  3 ++-
 2 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/app/models/issue_query.rb b/app/models/issue_query.rb
index 7e8c2e6a8..78ec9b61c 100644
--- a/app/models/issue_query.rb
+++ b/app/models/issue_query.rb
@@ -293,6 +293,33 @@ class IssueQuery < Query
       limit(options[:limit]).
       offset(options[:offset])
 
+    return preload_issues scope
+  rescue ::ActiveRecord::StatementInvalid => e
+    raise StatementInvalid.new(e.message)
+  end
+
+  # Like #issues, but returns an enumerator that lazily loads batches of issues
+  # Valid options are :order, :offset, :limit, :include, :conditions
+  def lazy_issues(options={})
+    issue_ids = self.issue_ids options
+
+    return Enumerator.new(issue_ids.length) do |yielder|
+
+      issue_ids.each_slice(500) do |chunked_ids|
+        # The FIELD() function is MySQL-specific
+        scope = Issue
+          .where(id: chunked_ids)
+          .order("FIELD(id,#{chunked_ids.join(',')})")
+
+        preload_issues(scope).each do |issue|
+          yielder << issue
+        end
+      end
+    end
+  end
+
+  # takes a scope, returns an array
+  def preload_issues(scope)
     scope = scope.preload([:tracker, :author, :assigned_to, :fixed_version, :category, :attachments] & columns.map(&:name))
     if has_custom_field_column?
       scope = scope.preload(:custom_values)
@@ -315,10 +342,9 @@ class IssueQuery < Query
     if has_column?(:last_notes)
       Issue.load_visible_last_notes(issues)
     end
-    issues
-  rescue ::ActiveRecord::StatementInvalid => e
-    raise StatementInvalid.new(e.message)
+    return issues
   end
+  private :preload_issues
 
   # Returns the issues ids
   def issue_ids(options={})
diff --git a/test/unit/query_test.rb b/test/unit/query_test.rb
index ee004232c..9d692f48e 100644
--- a/test/unit/query_test.rb
+++ b/test/unit/query_test.rb
@@ -161,7 +161,8 @@ class QueryTest < ActiveSupport::TestCase
 
   def assert_query_result(expected, query)
     assert_nothing_raised do
-      assert_equal expected.map(&:id).sort, query.issues.map(&:id).sort
+      assert_equal expected.map(&:id).sort, query.issues.map(&:id).sort, 'issues wrong'
+      assert_equal expected.map(&:id).sort, query.lazy_issues.map(&:id).sort, 'lazy issues wrong'
       assert_equal expected.size, query.issue_count
     end
   end
-- 
2.11.0