title: MongoDB Unique 10 digit ID
body: <p>I would like to create a unique 10 digit ID in MongoDB - for every user under a particular client that we get in our system. Note that we store all of our users (who are from different clients), under the same collection. The ID needs to be unique only among users of same client. Two users from two different clients, can share the same ID, even though they exist in the same collection.</p>
  
  <p>Any suggestions on how this 10 digit id can be unique for every user. </p>