fix inverse_of when find_or_initialize_by_*

inverse_of relation was not being set when calling find_or_initialize_by_ and the entry was
found on the db.

3 files changed, 22 insertions, 4 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 1fa891adc7..cf1f20c829 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## unreleased ##
 
+*   When calling the method .find_or_initialize_by_* from a collection_proxy
+    it should set the inverse_of relation even when the entry was found on the db.
+
+    *arthurnn*
+
 *   Callbacks on has_many should access the in memory parent if a inverse_of is set.
 
     *arthurnn*
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index 416a5823c6..62cdb1ea87 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -77,10 +77,12 @@ module ActiveRecord
       def method_missing(method, *args, &block)
         match = DynamicFinderMatch.match(method)
         if match && match.instantiator?
-          send(:find_or_instantiator_by_attributes, match, match.attribute_names, *args) do |r|
-            proxy_association.send :set_owner_attributes, r
-            proxy_association.send :add_to_target, r
-            yield(r) if block_given?
+          send(:find_or_instantiator_by_attributes, match, match.attribute_names, *args) do |record|
+            proxy_association.send :set_owner_attributes, record
+            proxy_association.send :add_to_target, record
+            yield(record) if block_given?
+          end.tap do |record|
+            proxy_association.send :set_inverse_instance, record
           end
 
         elsif target.respond_to?(method) || (!proxy_association.klass.respond_to?(method) && Class.respond_to?(method))
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index eec78f95c5..53cce33698 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -662,6 +662,17 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     end
   end
 
+  def test_inverse_after_find_or_initialize
+    firm = companies(:first_firm)
+    client = firm.clients_of_firm.find_or_initialize_by_client_of(firm.id)
+    assert_no_queries do
+      assert_equal firm, client.firm
+    end
+
+    firm.name = "A new firm"
+    assert_equal firm.name, client.firm.name
+  end
+
   def test_new_aliased_to_build
     company = companies(:first_firm)
     new_client = assert_no_queries { company.clients_of_firm.new("name" => "Another Client") }