Merge pull request #10796 from neerajdotname/10669

flatten merged join_values before building the joins

activerecord/CHANGELOG.md

+*   Flatten merged join_values before building the joins.
+   
+    While joining_values special treatment is given to string values.
+    By flattening the array it ensures that string values are detected
+    as strings and not arrays.
+
+    Fixes #10669.
+
+    *Neeraj Singh and iwiznia*
+
 *   Do not load all child records for inverse case.
 
     currently `post.comments.find(Comment.first.id)` would load all

activerecord/lib/active_record/relation/query_methods.rb

@@ -802,7 +802,7 @@ def arel
     def build_arel
       arel = Arel::SelectManager.new(table.engine, table)
 
-      build_joins(arel, joins_values) unless joins_values.empty?
+      build_joins(arel, joins_values.flatten) unless joins_values.empty?
 
       collapse_wheres(arel, (where_values - ['']).uniq)
 

activerecord/test/cases/relation_test.rb

@@ -176,7 +176,7 @@ def test_references_values_dont_duplicate
       assert_equal ['foo = bar'], relation.where_values
     end
 
-    def test_relation_merging_with_merged_joins
+    def test_relation_merging_with_merged_joins_as_symbols
       special_comments_with_ratings = SpecialComment.joins(:ratings)
       posts_with_special_comments_with_ratings = Post.group("posts.id").joins(:special_comments).merge(special_comments_with_ratings)
       assert_equal 3, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count.length
@@ -190,6 +190,13 @@ def test_respond_to_for_non_selected_element
       assert_equal false, post.respond_to?(:title), "post should not respond_to?(:body) since invoking it raises exception"
     end
 
+    def test_relation_merging_with_merged_joins_as_strings
+      join_string = "LEFT OUTER JOIN #{Rating.quoted_table_name} ON #{SpecialComment.quoted_table_name}.id = #{Rating.quoted_table_name}.comment_id"
+      special_comments_with_ratings = SpecialComment.joins join_string
+      posts_with_special_comments_with_ratings = Post.group("posts.id").joins(:special_comments).merge(special_comments_with_ratings)
+      assert_equal 3, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count.length
+    end
+
   end
 
   class RelationMutationTest < ActiveSupport::TestCase