Integrated next and previous methods for content in content types

app/models/content_instance.rb

@@ -50,6 +50,14 @@ class ContentInstance
   def visible?
     self._visible || self._visible.nil?
   end
+  
+  def next
+    content_type.contents.where(_position_in_list: _position_in_list + 1).first()
+  end
+  
+  def previous
+    content_type.contents.where(_position_in_list: _position_in_list - 1).first()
+  end
 
   def errors_to_hash
     Hash.new.replace(self.errors)

lib/locomotive/liquid/drops/content.rb

@@ -8,6 +8,14 @@ module Locomotive
         def _id
           self._source._id.to_s
         end
+        
+        def next
+          self._source.next.to_liquid
+        end
+        
+        def previous
+          self._source.previous.to_liquid
+        end
 
         def before_method(meth)
           return '' if self._source.nil?

spec/models/content_instance_spec.rb

@@ -41,6 +41,35 @@ describe ContentInstance do
     end
 
   end
+  
+  describe "#navigation" do
+    before(:each) do
+      %w(first second third).each_with_index do |item,index|
+        content = build_content({:title => item.to_s})
+        content._position_in_list = index
+        instance_variable_set "@#{item}", content
+      end
+    end
+    
+    it 'should find previous item when available' do
+      puts @second.previous
+      @second.previous.custom_field_1.should == "first"
+      @second.previous._position_in_list.should == 0
+    end
+    
+    it 'should find next item when available' do
+      @second.next.custom_field_1.should == "third"
+      @second.next._position_in_list.should == 2
+    end
+    
+    it 'should return nil when fetching previous item on first in list' do
+      @first.previous.should == nil
+    end
+    
+    it 'should return nil when fetching next item on last in list' do
+      @third.next.should == nil
+    end
+  end
 
   describe '#permalink' do