Rails database setup Polymorphism

Question

We have to create a request system which will have roughly 10 different types of requests. All of these requests will belong to the 'accounting' aspect of our application. Therefore we've called them "Accounting requests".

All requests share maybe only a few columns and each has up to 20 columns individually.

We started to wonder if having separate tables for each request type would be practical in terms of speed when we start to have to do very complicated joins or queries, for example, fetching ALL requests types into a single table and then sorting it.

Maybe it would be easier to just use Single Table Inheritance since it will have a type column and we'd be using one table to store all 10 accounting request types.

What do you think regarding using STI for this many polymorphic associations and requirements?

Essentially, it would have models like so:

AccountingRequest
BillingRequest < AccountingRequest
CheckRequest < AccountingRequest
CancellationRequest < AccountingRequest

Each subclass has roughly 10+ fields.

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Currently reading about Multiple Table Inheritance here. This seems like the solution that fits my requirements in this case. Not sure yet though.

Answer 1

STI is a good fit if your models all share the same attributes.

However if your sub classes start having attributes specific to them and not applicable to others, then STI can result in a lot of null columns. In that case, I usually prefer to go with polymorphic association.

This railscast episode is a great example of the difference between the 2