How to get last inserted id using the JS api? - mongodb

Question

Using the javascript api for MongoDB, how do you get the ID of the last inserted object? i.e.
obj = {a: 1, b: 2};
db.foo.insert(obj);
How do I get the ID for obj?

Answer 1

The people on #mongodb were helpful. The JS API doesn't currently support this, but you can use your own id. To generate a "normal" id, do _id: new ObjectId(). So the example in my question would be:
id = new ObjectId();
obj = {a: 1, b: 2, _id: id};
db.foo.insert(obj);

Answer 2

If you run
db.collection("venues").insert( {name: "test3", FSid: "test3"}, function( err, ret) {
console.log( ret )
})
it returns
{ result: { ok: 1, n: 1 },
ops: [ { name: 'test3', FSid: 'test3', _id: 57cb0a1162cecfe636df6fc1 } ],
insertedCount: 1,
insertedIds: [ 57cb0a1162cecfe636df6fc1 ] }
So you can get your ids along with all inserted objects through:
ret.ops[0]._id
or straight
ret.insertedIds[0]

Answer 3

Now，the mongo native js api supports this. You can get the last id like this:
collection.insert(line, {w : 1}, function(err, inserted) {
inserted[0]._id
}
insert sets the _id property on the inserted object, but it looks like you have to wait for the object to return. The best documentation I've found for this is (unfortunately) in the source code:
https://github.com/mongodb/node-mongodb-native/blob/master/lib/mongodb/collection.js

Answer 4

If you insert the data like this:
var temptodo = new User({
title: data.todo.text,
email: socket.handshake.email,
created_at: Date.now(),
completed: false,
sid: socket.handshake.sid
});
temptodo.save( function(error, User){
console.log("this is the id for the new todo. "+User._id);
console.log('Todo saved in database with sid: '+socket.handshake.sid);
});
Then you can grab the _id like this: console.log("this is the id for the new todo. "+User._id);