How complex a query can ActiveRecord handle before it's better using Raw SQL or a View???

rubyonrails-talk
1

Hi,

How complex a query can ActiveRecord handle before it’s better using Raw SQL or a View???

I need to calculate for example taxable income via a query going across 5 tables. Some like this: Find all transaction records (transactions table), for which they are allocated (via allocation table) to person X (person table), for transaction dates within date1 & date2, for which the category (categories table) associated with transaction, has a tax_id (from tax_codes table) of XYZ. I will need to reuse this type of query as I build a report of various tax categories.

Question - What would Rails best practice way for the above?

[I’m thinking best to create a flat view of this and use this to then query against]

Thanks

2

Hi,

How complex a query can ActiveRecord handle before it's better using
Raw SQL or a View???

Depends what you mean by handle. If you mean "will ruby run out of
steam" then that's purely a function of the result set, instantiating
1 million ActiveRecord objects is probably not a good idea. If you mean handle as in get ActiveRecord to generate it without
writing any sql yourself then I don't believe there's a hard and fast
rule or anything like that. You might be able to get away with

Transaction.find :all, :joins => [:category, {:allocation => :person}],            :conditions => {'people.id' => bob, 'categories.tax_id' =>
1234, 'transactions.created_at' => (1.week.ago .. Time.now)}

or maybe the relations you need to express don't quite map to those
things activerecord makes easy. It's a case by case thing, much as I'd
far write the above than write the equivalent sql, I wouldn't waste
time trying to force activerecord through hoops when it was clear that
it wasn't time well spent.

Fred

3

I was asking I guess from the point of view of: (a) maintainability/readability of the code (i.e. keeping things simple) and (b) to a lesser extent performance (i.e. if ActiveRecord wasn’t going to be good at handling a complex query well from a performance point of view)

4

I was asking I guess from the point of view of: (a) maintainability/readability of the code (i.e. keeping things
simple) and

I don't think how complex is the right question. There are some very
complex things you can generate very easily, as well as easier things
where you might have to fight activerecord.

(b) to a lesser extent performance (i.e. if ActiveRecord wasn't
going to be good at handling a complex query well from a performance
point of view)

That's sort of what I started with. Performance wise, Active Record is
only going to care about the size of the result set really. After all
it's the database, not active record that has to do the 27 joins or
whatever it is.

Fred

5

thanks Fred - you’ve help me realise that the “:joins” option can be used in a Rails like sense (i.e. as well as with SQL) so I’ll try this way first