migration_cars_imagesize.js

var cars = db.cars.find().toArray();
for (var i in cars) { 
  var car = cars[i]; 
  car.imageSize = { w: 128, h: 64 };  // faut mettre quoi ici ? :p
  /* afficher */ 
  printjson(car); 
  /* sauvegarder (on peut car _id est present) */ 
  db.cars.save(car) 
}