added CouchRest::Model#attachment_url for someone to fetch the attachment using other means

lib/couchrest/core/model.rb

@@ -536,10 +536,17 @@ module CouchRest
       self['_attachments'].delete attachment_name
     end
     
+    # returns true if attachment_name exists
     def has_attachment?(attachment_name)
       !!(self['_attachments'] && self['_attachments'][attachment_name] && !self['_attachments'][attachment_name].empty?)
     end
 
+    # returns URL to fetch the attachment from
+    def attachment_url(attachment_name)
+      return unless has_attachment?(attachment_name)
+      "#{database.root}/#{self.id}/#{attachment_name}"
+    end
+
     protected
 
     # Saves a document for the first time, after running the before(:create)

spec/couchrest/core/model_spec.rb

@@ -834,4 +834,22 @@ describe CouchRest::Model do
       lambda{Basic.get(@obj.id).read_attachment(@attachment_name)}.should raise_error
     end
   end
+  
+  describe "#attachment_url" do
+    before(:each) do
+      @obj = Basic.new
+      @file = File.open(FIXTURE_PATH + '/attachments/test.html')
+      @attachment_name = 'my_attachment'
+      @obj.create_attachment(:file => @file, :name => @attachment_name)
+      @obj.save.should == true
+    end
+    
+    it 'should return nil if attachment does not exist' do
+      @obj.attachment_url('bogus').should be_nil
+    end
+    
+    it 'should return the attachment URL as specified by CouchDB HttpDocumentApi' do
+      @obj.attachment_url(@attachment_name).should == "#{Basic.database}/#{@obj.id}/#{@attachment_name}"
+    end
+  end
 end