arangosh> a1 = db.example.insert({"a" : 1});
{ 
  "error" : false, 
  "_id" : "example/48063938", 
  "_rev" : "48063938", 
  "_key" : "48063938" 
}
arangosh> a2 = db.example.update("example/18612115", { "x" : 1, "y" : 2 });
{ 
  "error" : false, 
  "_id" : "example/18612115", 
  "_rev" : "48457154", 
  "_key" : "18612115" 
}