Mongodb – Structuring data in MongoDB for a to-do list type application

database-designmongodb

This is a fairly high level question as I am in the initial stages of planning this application, and am also very new to MongoDB and document-based databases in general. Disclaimer aside, I am building a to-do list type application whose two main types of data are users and items (aka tasks or todo's), and my question is, what would be a good way to structure this data in mongodb, if I want it optimized more for read speeds rather than updates?

My initial thought, based on my limited knowledge of mongodb, is that since it allows embedded type data structures I could basically store it in a single collection like this:

{
    username: "joe",
    password: "...",
    items: [
        {
            text: "This is a task",
            completed: 1
        },
        ...
    ]
},
...

However, will this make it more difficult to update/remove existing items since they are not themselves stored as separate documents, and therefore lose things like auto-generated unique object ID's, ect? Also each user could potentially have a relatively large number of items associated with them (possibly 1000's). Is embedding large lists in parent documents like that a bad idea?

Best Answer

creating a sub collection should offer better read performance see http://docs.mongodb.org/manual/core/data-modeling/

I think it would be a good idea to add an id to each subdocument so it is easier to access it (because from your schema you may have identical items)

like: 

{
    username: "joe",
    password: "...",
    items: [
        subid:{
            text: "This is a task",
            completed: 1
        },
        ...
    ]
},
...

you can use subid = ObjectId() to autogenerate ids, or create this in your application.

I don't think there is a problem with having thousands of items in a document just remember that the maximum document size is 16 megabytes.

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