How do I access inserted document's _id within a transaction in ArangoDB -

i don't see examples of accessing inserted/updated documents key's when in transaction.

var collections = {write: ['foo','bar']}; var action = string(function () {     var doc = params['doc'];     var relateddoc = params['relateddoc'];     var db = require('internal').db;     db.foo.save(doc); // how access _id, key etc of newly inserted doc?     relateddoc.foos.push(doc._id); // _id not exist yet     db.bar.save(relateddoc);     return {success: true}; }); var params = {     doc: doc,     relateddoc: relateddoc }; db.transaction(collections, action, params, function (err, result) {     if (err) {         return dfd.reject(err);     }     return dfd.resolve(result); }); 

the collection.save() method return meta-data saved document:

• _rev: document revision id (auto-generated server)
• _key: document key (either specified user in _key attribute or auto-generated server if not)
• _id: same key, including collection name

to use generated id in code, can capture result of collection.save() in variable , use follows:

var collections = {write: ['foo','bar']}; var action = string(function () {     var doc = params['doc'];     var relateddoc = params['relateddoc'];     var db = require('internal').db;     var newdoc = db.foo.save(doc);     // capture result of save in newdoc     relateddoc.foos.push(newdoc._id);  // use newdoc._id      db.bar.save(relateddoc);     return {success: true}; }); var params = {     doc: doc,     relateddoc: relateddoc }; db.transaction(collections, action, params, function (err, result) {     if (err) {       return dfd.reject(err);     }     return dfd.resolve(result); });