`CollectionAssociation#empty?` respects newly builded records

3 files changed, 19 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 5a0c391154..68ed6cdf51 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,16 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Collection associations `#empty?` always respects builded records.
+    Fix #8879.
+
+    Example:
+
+        widget = Widget.new
+        widget.things.build
+        widget.things.empty? # => false
+
+    *Yves Senn*
+
 *   Remove support for parsing YAML parameters from request.
 
     *Aaron Patterson*
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 832b963052..5feb149946 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -273,7 +273,7 @@ module ActiveRecord
         if loaded? || options[:counter_sql]
           size.zero?
         else
-          !scope.exists?
+          @target.blank? && !scope.exists?
         end
       end
 
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 7e6c7d5862..28400970fb 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -625,6 +625,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal 3, company.clients_of_firm.size
   end
 
+  def test_collection_not_empty_after_building
+    company = companies(:first_firm)
+    assert_predicate company.contracts, :empty?
+    company.contracts.build
+    assert_not_predicate company.contracts, :empty?
+  end
+
   def test_collection_size_twice_for_regressions
     post = posts(:thinking)
     assert_equal 0, post.readers.size