title: Use official identification card id or generated id's from MongoDB for identifying users?
body: <p>I am designing the schema for a simple MongoDB database where there will be a collection for customers.</p>
  
  <p>Natural way of identifying customer will be use their official identification card id (6 numbers and a letter, unique for each person in the country). Another way of doing will be letting MongoDB to choose the _id field value and using the card id as another field.</p>
  
  <p>Any suggestion of advantages / disadvantages of choosing one string with 6 numbers and a letter as _id, or choosing and ObjectId created by Mongo?</p>