title: appengine datastore change entities property
body: <p>I would like to change the entity property from String to long. I have seen Nick answering similar problem in <a href="https://stackoverflow.com/questions/4742875/change-integerproperty-to-floatproperty-of-existing-appengine-datastore">Change IntegerProperty to FloatProperty of existing AppEngine DataStore</a> but I am writing in Java and need some code example since I don't know anything about the mapreduce. </p>
  
  <p>e.g. we want to change userId from String to Long of <a href="http://code.google.com/p/cloud-tasks-io/source/browse/trunk/CloudTasks-AppEngine/src/com/cloudtasks/server/Task.java" rel="nofollow noreferrer">this class</a>.</p>
  
  <p>I also would like to get advice on my thinking of storing date in long instead of String so that the time information can be consumed readily from android, GWT and more(over Rest Json or RPC). Right now, GWT does not have Jodatime and it has limited support of Java.util.Date and parsing.</p>