Add an Option to Ignore Missing Types

lib/replicate/loader.rb

@@ -71,11 +71,17 @@ def read(io)
     # Returns the new object instance.
     def load(type, id, attributes)
       model_class = constantize(type)
+
+      return if model_class.nil?
+
       translate_ids type, id, attributes
       begin
         new_id, instance = model_class.load_replicant(type, id, attributes)
       rescue => boom
         warn "error: loading #{type} #{id} #{boom.class} #{boom}"
+
+        return if ignore_missing?
+
         raise
       end
       register_id instance, type, id, new_id
@@ -123,6 +129,15 @@ def register_id(object, type, remote_id, local_id)
       end
     end
 
+    # Silently ignore missing replication types instead of raising an
+    # uninitialized constant error. Allows for replication between mismatched
+    # object graphs.
+    def ignore_missing!
+      @ignore = true
+    end
+
+    def ignore_missing? ; @ignore ; end
+
     # Turn a string into an object by traversing constants. Identical to
     # ActiveSupport's String#constantize implementation.
     if Module.method(:const_get).arity == 1
@@ -132,7 +147,15 @@ def constantize(string)
           if namespace.const_defined?(name)
             namespace.const_get(name)
           else
-            namespace.const_missing(name)
+            begin
+              namespace.const_missing(name)
+            rescue NameError => e
+              if ignore_missing?
+                warn "ignoring missing type #{name}"
+              else
+                raise e
+              end
+            end
           end
         end
       end
@@ -143,7 +166,15 @@ def constantize(string)
           if namespace.const_defined?(name, false)
             namespace.const_get(name)
           else
-            namespace.const_missing(name)
+            begin
+              namespace.const_missing(name)
+            rescue NameError => e
+              if ignore_missing?
+                warn "ignoring missing type #{name}"
+              else
+                raise e
+              end
+            end
           end
         end
       end

test/loader_test.rb

@@ -90,4 +90,40 @@ def test_translating_multiple_id_attributes
     assert_equal 11, objects.size
     assert_equal 10, objects.last.related.size
   end
+
+  def test_ignoring_a_missing_type
+    dumper = Replicate::Dumper.new
+
+    objects = []
+    dumper.listen { |type, id, attrs, obj| objects << [type, id, attrs, obj] }
+
+    with_ghost_class do |klass|
+      dumper.dump(klass.new)
+    end
+
+    begin
+      objects.each { |type, id, attrs, obj| @loader.feed type, id, attrs }
+
+      assert_fail "NameError unexpectedly ignored"
+    rescue NameError
+    end
+
+    @loader.ignore_missing!
+
+    objects.each { |type, id, attrs, obj| @loader.feed type, id, attrs }
+  end
+
+  def with_ghost_class
+    eval <<-RUBY
+      class ::Ghost
+        def dump_replicant(dumper)
+          dumper.write self.class, 3, {}, self
+        end
+      end
+    RUBY
+
+    yield Ghost
+  ensure
+    Object.send(:remove_const, :Ghost)
+  end
 end