Question

Trying to figure out the best way to set up collection “lists” for users given the following data (pseudo code):

user table = id, name, email

cars table = id, make, model

user_cars table = user_id, car_id, rating

collections table = id, user_id, name

Facts:

• Users can have many cars

• Users can have many collections

• Individual cars can be in many collections

The 2 options I see for allowing the user to have a list of collections are to either add a field to user_cars called collection_list and make the contents of that field a comma-sep list of collections that the user owns, like: 1,30,400

or to add an additional table called collection_entries which contains collection_id, and car_id, each pointing to their respective collections.id and cars.id. The possible problem I see with adding another table is that the number of rows will get huge in that table. eg: 10,000 users x 10 collections each x 100 cars per collection = 1 million rows.

Ideas?

Answer 1

If I understand correctly a collection has precisely 1 owner?

So:

users: user_id, name

cars: car_id, name

collection_cars: collectioncar_id, collection_id, car_id

collections: collection_id, user_id, name

So for each collection you store which cars are in them in a seperate table. I don’t think 1 million rows will be such a big problem if you use indices correctly.
I don’t think it’s a good idea in general to give up on a good database design because you’re scared of having many rows. Databases are designed to handle large datasets, so that’s what you can use them for. Secondly; if you store for each user which car they own, you will also have to store to which collection that car belongs, so you won’t gain anything.