Why autoform after insert get different id from collection hook before insert?

1

this is my code

    Ice.Collection.Order.before.insert(function (userId, doc){
     var prefix = doc.branchId + '-';
     doc._id = idGenerator.genWithPrefix(Ice.Collection.Order, prefix, 12);
});

—autoform hook—

after:{
 insert: function(err,id){
  console.log(id)
}

}