Add document to an embedded document array - node.js

Question

I'm trying to add an embedded document to an existing document field. I found one fitting answer with the search but I'm running into errors. I'm using node.js, Express and Mongoose.
My database schemas:
var entry = new Schema({
name : { type : String, required : true},
description : { type : String, default: ""},
});
var compo = new Schema({
name : String,
description : String,
entries : [entry]
});
And I'm trying to update the entries array with the following code
var entry = new entryModel();
entry.name = "new name";
entry.description= "new description";
compoModel.findOne(query, function (err, item) {
if (item) {
item.entries.push(entry);
item.save(function (err) {
if (!err) {
log.debug('Entry added successfully.');
} else {
log.error("Mongoose couldn't save entry: " + err);
}
});
}
});
It yields an error: TypeError: Object.keys called on non-object
What have I missed?

Answer 1

So I managed to get it working via the Model.update method by simply adding a new object to the compo.entries list and calling compoModel.update.

Answer 2

My similar issue (same error) was solved by clearing the sub-document array. It was populated prior to the definition of the sub-document scheme. At least this is what i think happened.
E.g.:
var token = new Schema( { value: String, expires: Date } )
var user = new Schema( { username: String, tokens: [token] } )
.. and, prior to defining the 'token' scheme i had entries such as:
{ username: 'foo', tokens: ['123456'] }
.. so, clearing tokens did it for me.
user.tokens = []
user.save()