diff --git a/lib/oat/adapters/json_api.rb b/lib/oat/adapters/json_api.rb
index 7431958..c8ca40b 100644
--- a/lib/oat/adapters/json_api.rb
+++ b/lib/oat/adapters/json_api.rb
@@ -71,7 +71,7 @@ def meta(key, value)
 
       def entity(name, obj, serializer_class = nil, context_options = {}, &block)
         ent = serializer_from_block_or_class(obj, serializer_class, context_options, &block)
-        if ent
+        if ent && !serializer.serialized?(name, ent.item.id)
           ent_hash = ent.to_hash
           _name = entity_name(name)
           entity_hash[_name.to_s.pluralize.to_sym] ||= []
@@ -80,8 +80,9 @@ def entity(name, obj, serializer_class = nil, context_options = {}, &block)
         end
       end
 
-      def entities(name, collection, serializer_class = nil, context_options = {}, &block)
+      def entities(name, collection, serializer_class = nil, context_options = nil, &block)
         return if collection.nil? || collection.empty?
+        context_options ||= {}
         _name = entity_name(name)
         link_name = _name.to_s.pluralize.to_sym
         data[:links][link_name] = []
@@ -89,7 +90,7 @@ def entities(name, collection, serializer_class = nil, context_options = {}, &bl
         collection.each do |obj|
           entity_hash[link_name] ||= []
           ent = serializer_from_block_or_class(obj, serializer_class, context_options, &block)
-          if ent
+          if ent && !serializer.serialized?(link_name, ent.item.id)
             ent_hash = ent.to_hash
             data[:links][link_name] << ent_hash[:id]
             entity_hash[link_name] << ent_hash
@@ -104,13 +105,19 @@ def entity_name(name)
 
       private :entity_name
 
-      def collection(name, collection, serializer_class = nil, context_options = {}, &block)
+      def collection(name, collection, serializer_class = nil, context_options = nil, &block)
+        context_options ||= {}
         @treat_as_resource_collection = true
         data[:resource_collection] = [] unless data[:resource_collection].is_a?(Array)
 
         collection.each do |obj|
           ent = serializer_from_block_or_class(obj, serializer_class, context_options, &block)
-          data[:resource_collection] << ent.to_hash if ent
+          if ent
+            unless serializer.serialized?(root_name, ent.item.id)
+              # serializer.set_serialized(root_name, ent.item.id)
+              data[:resource_collection] << ent.to_hash
+            end
+          end
         end
       end
 
diff --git a/lib/oat/serializer.rb b/lib/oat/serializer.rb
index adceb68..86e11a6 100644
--- a/lib/oat/serializer.rb
+++ b/lib/oat/serializer.rb
@@ -4,6 +4,10 @@ class Serializer
 
     class_attribute :_adapter, :logger
 
+    class << self
+      attr_accessor :type
+    end
+
     def self.schema(&block)
       @schema = block if block_given?
       @schema || Proc.new{}
@@ -20,11 +24,16 @@ def self.warn(msg)
 
     attr_reader :item, :context, :adapter_class, :adapter
 
-    def initialize(item, context = {}, _adapter_class = nil, parent_serializer = nil)
-      @item, @context = item, context
+    def initialize(item, context = nil, _adapter_class = nil, parent_serializer = nil)
+      @item = item
+      @context = context || {}
       @parent_serializer = parent_serializer
       @adapter_class = _adapter_class || self.class.adapter
       @adapter = @adapter_class.new(self)
+      if self.class.type
+        type(self.class.type)
+      end
+      @context[:_serialized_entities] ||= {}
     end
 
     def top
@@ -51,6 +60,9 @@ def respond_to_missing?(method_name, include_private = false)
 
     def to_hash
       @to_hash ||= (
+        if self.class.type
+          Array(item).each { |i| set_serialized(self.class.type, i.id) }
+        end
         instance_eval(&self.class.schema)
         adapter.to_hash
       )
@@ -65,5 +77,16 @@ def map_property(name)
       property name, value
     end
 
+    def set_serialized(type, id)
+      @context[:_serialized_entities][type] ||= {}
+      @context[:_serialized_entities][type][id] = true
+    end
+
+    def serialized?(type, id)
+      h = @context[:_serialized_entities]
+      h = h[type] if h
+      h[id] if h
+    end
+
   end
 end