Mongoose findOne embedded document by _id - node.js

Question

I am trying to push menus to the embedded document. But I am getting not defined findOne in restaurant. I just want to push some documents into the restaurant's menu categories. As you can see in the schema:
var RestaurantSchema = new mongoose.Schema({
contactTelphone : String,
address : String,
branchID : String,
email : String,
restaurantName : String,
userID : String,
menuCategory : [MenuCategorySchema]
});
var MenuCategorySchema = new mongoose.Schema({
menuCategory : String,
menuCategoryAlt : String,
sequence : Number,
menus : [MenuSchema],
restaurantInfo : { type: Schema.Types.ObjectId, ref: 'Restaurant' },
});
var MenuSchema = new mongoose.Schema({
foodName : String,
foodNameAlt : String,
picName : String,
price : String,
rating : Number,
menuSequence : Number,
category : { type: Schema.Types.ObjectId, ref: 'MenuCategory' },
});
exports.menuForMenuCategory = function(newData, callback)
{
console.log(newData);
var menuCategoryId = newData.menuCategoryId;
var restaurantId = newData.restaurantId;
var newMenu = new Menu({
foodName : newData.foodName,
foodNameAlt : newData.foodNameAlt,
picName : newData.picName,
price : newData.price,
cookingCategory : newCookingCategory,
dishSpecial : newDishSpeical
});
Restaurant.findOne( {'_id' : restaurantId }, function(err, restaurant){
if (!err) {
//Is it how to do this? It says "findOne not defined"
restaurant.findOne( "_id" : menuCategoryId, function(err, category){
category.push(newMenu);
});
}
});
}

Answer 1

Subdocuments have an .id() method so you can do this:
myModel.findById(myDocumentId, function (err, myDocument) {
var subDocument = myDocument.mySubdocuments.id(mySubDocumentId);
});
See http://mongoosejs.com/docs/subdocs.html for reference.

Answer 2

restaurant is just an object containing the result to your query. It does not have a findOne method, only Restaurant does.
Since, MenuCategory is just a sub-document of Restaurant, this will come pre-populated whenever you retrieve a restaurant. E.g.
Restaurant.findById(restaurantId, function(err, restaurant){
console.log(restaurant.menuCategory);
// Will show your array of Menu Categories
// No further queries required
});
Adding a new Menu Category is a matter of pushing a new MenuCategory instance to the menuCategory array and saving the restaurant. This means the new menu category is saved with the restaurant and not in a separate collection. For example:
Restaurant.findById(restaurantId, function(err, restaurant){
// I'm assuming your Menu Category model is just MenuCategory
var anotherMenuCategory = new MenuCategory({
menuCategory: "The name",
menuCategoryAlt: "Alternative name",
sequence: 42,
menus: []
});
restaurant.menuCategory.push(anotherMenuCategory);
restaurant.save(); // This will save the new Menu Category in your restaurant
});
Saving a menu to a menu category follows the same procedure since, according to your schema, Menus are embedded sub-documents within each MenuCategory. But note that you need to save the restaurant as its the restaurant collection that is storing all your menus and menu categories as sub-documents
Having answered your question (I hope) I should also point out your schema design should be rethought. Having sub-documents nested within sub-documents is arguably not a good idea. I think I can see where you're coming from - you're trying to implement a SQL-like many-to-one association within your schemas. But this isn't necessary with NoSQL databases - the thinking is somewhat different. Here are some links to some SO questions about efficient schema design with NoSQL databases:
MongoDB Schema Design - Many small documents or fewer large
documents?
How should I implement this schema in MongoDB?
MongoDB relationships: embed or reference?