a user can insert a document one time into a collection, after that, the insert is denied

insertonlyonce.js

// some random collection
Things = new Meteor.Collection('things');

// collection used to track users who are blocked from inserting
Blocked = new Meteor.Collection('blocked');

if (Meteor.isServer) {
  Meteor.startup(function () {
    // remove all documents on startup for testing purposes
    Blocked.remove({});
    Things.remove({});
  });

  // allow inserting generally...
  Things.allow({
    insert: function () {
      return true;
    }
  });

  // track inserting in Blocked collection, only allow one insert on Things per userId
  Things.deny({
    insert: function (userId, doc) {
      if (Blocked.findOne({userId: userId})) {
        return true;
      } else {
        Blocked.insert({userId: userId});
        return false;
      }
    }
  });
}