Ensure belongs_to finder method sends a non-nil key

lib/active_resource/associations.rb

@@ -14,7 +14,7 @@ module Builder
   # === Options
   # [:class_name]
   #   Specify the class name of the association. This class name would
-  #   be used for resolving the association class. 
+  #   be used for resolving the association class.
   #
   # ==== Example for [:class_name] - option
   # GET /posts/123.json delivers following response body:
@@ -48,7 +48,7 @@ def has_many(name, options = {})
   # === Options
   # [:class_name]
   #   Specify the class name of the association. This class name would
-  #   be used for resolving the association class. 
+  #   be used for resolving the association class.
   #
   # ==== Example for [:class_name] - option
   # GET /posts/1.json delivers following response body:
@@ -74,7 +74,7 @@ def has_one(name, options = {})
   end
 
   # Specifies a one-to-one association with another class. This class should only be used
-  # if this class contains the foreign key. 
+  # if this class contains the foreign key.
   #
   # Methods will be added for retrieval and query for a single associated object, for which
   # this object holds an id:
@@ -83,7 +83,7 @@ def has_one(name, options = {})
   #   Returns the associated object. +nil+ is returned if the foreign key is +nil+.
   #   Throws a ActiveResource::ResourceNotFound exception if the foreign key is not +nil+
   #   and the resource is not found.
-  # 
+  #
   # (+association+ is replaced with the symbol passed as the first argument, so
   # <tt>belongs_to :post</tt> would add among others <tt>post.nil?</tt>.
   #
@@ -130,8 +130,8 @@ def defines_belongs_to_finder_method(method_name, association_model, finder_key)
         instance_variable_get(ivar_name)
       elsif attributes.include?(method_name)
         attributes[method_name]
-      else
-        instance_variable_set(ivar_name, association_model.find(send(finder_key)))
+      elsif association_id = send(finder_key)
+        instance_variable_set(ivar_name, association_model.find(association_id))
       end
     end
   end
@@ -149,7 +149,7 @@ def defines_has_many_finder_method(method_name, association_model)
       end
     end
   end
-  
+
   # Defines the has_one association
   def defines_has_one_finder_method(method_name, association_model)
     ivar_name = :"@#{method_name}"

test/cases/association_test.rb

@@ -58,4 +58,22 @@ def test_defines_belongs_to_finder_method_with_instance_variable_cache
     2.times{person.customer}
     assert person.instance_variable_defined?(:@customer)
   end
+
+  def test_belongs_to_with_finder_key
+    Person.defines_belongs_to_finder_method(:customer, Customer, 'customer_id')
+
+    person = Person.new
+    person.stubs(:customer_id).returns(1)
+    Customer.expects(:find).with(1).once()
+    person.customer
+  end
+
+  def test_belongs_to_with_nil_finder_key
+    Person.defines_belongs_to_finder_method(:customer, Customer, 'customer_id')
+
+    person = Person.new
+    person.stubs(:customer_id).returns(nil)
+    Customer.expects(:find).with(nil).never()
+    person.customer
+  end
 end