5 files changed, 32 insertions, 1 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 6d4ea2b682..5797d62441 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,12 @@
+*   `ActiveRecord::Relation::Merger#filter_binds` now compares equivalent symbols and
+    strings in column names as equal.
+
+    This fixes a rare case in which more bind values are passed than there are
+    placeholders for them in the generated SQL statement, which can make PostgreSQL
+    throw a `StatementInvalid` exception.
+
+    *Nat Budin*
+
 *   Fix `stored_attributes` to correctly merge the details of stored
     attributes defined in parent classes.
 
diff --git a/activerecord/lib/active_record/relation/merger.rb b/activerecord/lib/active_record/relation/merger.rb
index fcb28a18f6..ac41d0aa80 100644
--- a/activerecord/lib/active_record/relation/merger.rb
+++ b/activerecord/lib/active_record/relation/merger.rb
@@ -156,7 +156,7 @@ module ActiveRecord
       def filter_binds(lhs_binds, removed_wheres)
         return lhs_binds if removed_wheres.empty?
 
-        set = Set.new removed_wheres.map { |x| x.left.name }
+        set = Set.new removed_wheres.map { |x| x.left.name.to_s }
         lhs_binds.dup.delete_if { |col,_| set.include? col.name }
       end
 
diff --git a/activerecord/test/cases/relation/merging_test.rb b/activerecord/test/cases/relation/merging_test.rb
index 48f45d45b1..2b5c2fd5a4 100644
--- a/activerecord/test/cases/relation/merging_test.rb
+++ b/activerecord/test/cases/relation/merging_test.rb
@@ -108,6 +108,11 @@ class RelationMergingTest < ActiveRecord::TestCase
     merged = left.merge(right)
     assert_equal post, merged.first
   end
+
+  def test_merging_compares_symbols_and_strings_as_equal
+    post = PostThatLoadsCommentsInAnAfterSaveHook.create!(title: "First Post", body: "Blah blah blah.")
+    assert_equal "First comment!", post.comments.where(body: "First comment!").first_or_create.body
+  end
 end
 
 class MergingDifferentRelationsTest < ActiveRecord::TestCase
diff --git a/activerecord/test/models/comment.rb b/activerecord/test/models/comment.rb
index f82df417ce..bf0162d09b 100644
--- a/activerecord/test/models/comment.rb
+++ b/activerecord/test/models/comment.rb
@@ -40,3 +40,11 @@ end
 
 class VerySpecialComment < Comment
 end
+
+class CommentThatAutomaticallyAltersPostBody < Comment
+  belongs_to :post, class_name: "PostThatLoadsCommentsInAnAfterSaveHook", foreign_key: :post_id
+
+  after_save do |comment|
+    comment.post.update_attributes(body: "Automatically altered")
+  end
+end
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index b1e56c14d1..5f01ab0a82 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -208,3 +208,12 @@ class SpecialPostWithDefaultScope < ActiveRecord::Base
   self.table_name = 'posts'
   default_scope { where(:id => [1, 5,6]) }
 end
+
+class PostThatLoadsCommentsInAnAfterSaveHook < ActiveRecord::Base
+  self.table_name = 'posts'
+  has_many :comments, class_name: "CommentThatAutomaticallyAltersPostBody", foreign_key: :post_id
+
+  after_save do |post|
+    post.comments.load
+  end
+end