Question

I am trying to design a simple application where in I have two entities Notebook and Note. So Notebook can contain multiple Notes.In RDBMS I could have two tables and have One to Many
relationship between them. I am not sure in MongoDB whether I should not take a two collection
approach or I should embed notes in Notebook collection. What would you suggest?

Answer 1

That seems like a perfectly reasonable situation to use a single collection called Notebook, and each Notebook document contains embedded Notes. You can easily index on embedded documents.

If a Notebook document has a ‘notes’ key, and value is a list of notes:

{
    "notes": [
        {"created_on": Date(1343592000000), text: "A note."}
    ]
}

# create index
db.notebook.ensureIndex({"notes.created_on" : -1})

My opinion is to try and embed as much as possible, and then choose to reference another collection via an id as a second option when the reference needs to be to a more general set of data that is shared and might change. For instance, a collection of category documents which many other collections reference. And the category can be updated over time. But in your case, a note should always belong to a note book