Fixed regression with referencing polymorphic assoc in eager-load

This is cased by 03118bc + 9b5d603. The first commit referenced the undefined
local variable `column` when it should be using `reflection.type` as the lookup
key. The second commit changed `build_arel` to not modify the `bind_values` in-
place so we need to combine the arel's `bind_values` with the relation's when
building the SQL.

Fixes #16591

Related #15821 / #15892 / 7aeca50

3 files changed, 13 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/associations/join_dependency/join_association.rb b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
index c3bbdccad8..e7d3c9ba40 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_association.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -65,7 +65,7 @@ module ActiveRecord
 
             if reflection.type
               value = foreign_klass.base_class.name
-              column = klass.columns_hash[column.to_s]
+              column = klass.columns_hash[reflection.type.to_s]
 
               substitute = klass.connection.substitute_at(column, bind_values.length)
               bind_values.push [column, value]
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index a7899da3a8..b1753b27e1 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -401,8 +401,9 @@ module ActiveRecord
         "#{quoted_table_name}.#{quoted_primary_key}", relation.order_values)
 
       relation = relation.except(:select).select(values).distinct!
+      arel = relation.arel
 
-      id_rows = @klass.connection.select_all(relation.arel, 'SQL', relation.bind_values)
+      id_rows = @klass.connection.select_all(arel, 'SQL', arel.bind_values + relation.bind_values)
       id_rows.map {|row| row[primary_key]}
     end
 
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 21912fdf0f..b852bd3536 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -1290,4 +1290,14 @@ class EagerAssociationTest < ActiveRecord::TestCase
     david = Author.where(id: "1").eager_load(:readonly_comments).first!
     assert david.readonly_comments.first.readonly?
   end
+
+  test "preloading a polymorphic association with references to the associated table" do
+    post = Post.includes(:tags).references(:tags).where('tags.name = ?', 'General').first
+    assert_equal posts(:welcome), post
+  end
+
+  test "eager-loading a polymorphic association with references to the associated table" do
+    post = Post.eager_load(:tags).where('tags.name = ?', 'General').first
+    assert_equal posts(:welcome), post
+  end
 end