From c691be6c9b4b25dea291ea4cfe7ea9b0de773c89 Mon Sep 17 00:00:00 2001
From: Gleb Mazovetskiy <glex.spb@gmail.com>
Date: Thu, 6 Jun 2019 06:18:11 +0100
Subject: [PATCH] Fix preload_first_topic_post on empty association

Reported in https://github.com/thredded/thredded/commit/f1874fba333444255979c0789ba17f8dc24a4d6f#r33825204
---
 app/models/concerns/thredded/post_common.rb         | 1 +
 app/models/thredded/post_moderation_record.rb       | 1 +
 spec/models/thredded/post_moderation_record_spec.rb | 9 +++++++++
 3 files changed, 11 insertions(+)
 create mode 100644 spec/models/thredded/post_moderation_record_spec.rb

diff --git a/app/models/concerns/thredded/post_common.rb b/app/models/concerns/thredded/post_common.rb
index 8cc564e4d..379be7f26 100644
--- a/app/models/concerns/thredded/post_common.rb
+++ b/app/models/concerns/thredded/post_common.rb
@@ -22,6 +22,7 @@ module PostCommon
         posts_table_name = quoted_table_name
         result = all
         owners_by_id = result.each_with_object({}) { |r, h| h[r.postable_id] = r.postable }
+        next result if owners_by_id.empty?
         preloader = ActiveRecord::Associations::Preloader.new.preload(
           owners_by_id.values, :first_post,
           unscoped.where(<<~SQL.delete("\n"))
diff --git a/app/models/thredded/post_moderation_record.rb b/app/models/thredded/post_moderation_record.rb
index 0ddd6b504..978d7e675 100644
--- a/app/models/thredded/post_moderation_record.rb
+++ b/app/models/thredded/post_moderation_record.rb
@@ -31,6 +31,7 @@ class PostModerationRecord < ActiveRecord::Base
       posts_table_name = Thredded::Post.quoted_table_name
       result = all
       owners_by_id = result.each_with_object({}) { |r, h| h[r.post.postable_id] = r.post.postable }
+      next result if owners_by_id.empty?
       preloader = ActiveRecord::Associations::Preloader.new.preload(
         owners_by_id.values, :first_post,
         Thredded::Post.unscoped.where(<<~SQL.delete("\n"))
diff --git a/spec/models/thredded/post_moderation_record_spec.rb b/spec/models/thredded/post_moderation_record_spec.rb
new file mode 100644
index 000000000..285f63a2c
--- /dev/null
+++ b/spec/models/thredded/post_moderation_record_spec.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Thredded::PostModerationRecord do
+  it 'empty preload_first_topic_post' do
+    expect { described_class.preload_first_topic_post.to_a }.not_to raise_error
+  end
+end