Rails 4 string interpolation in raw SQL request - ruby-on-rails

Question

What would be the best way of rewriting this query without interpolation?
def case_joins(type)
subquery = <<-SQL.squish
SELECT id FROM cases c2
WHERE c2.title_id = titles.id AND c2.value = 0 AND c2.type = '#{type}'
ORDER BY c2.created_at DESC LIMIT 1
SQL
"LEFT OUTER JOIN cases ON cases.title_id = titles.id AND cases.value = 0 AND cases.type = '#{type}' AND cases.id = (#{subquery})"
end

Answer 1

I'm assuming that you want to avoid interpolation of variables, which is dangerous since its open to SQL injection. I would simply join onto the cases selected from the subquery instead of putting the subquery into the WHERE conditions. This does involve interpolation, but only of AR-generated SQL. I would also implement it as a scope to leverage AR scope chaining:
class Title < ActiveRecord::Base
def self.case_joins(type)
case_query = Case.from("cases c").where(c: {title_id: title_id, value: 0, type: type}).order('c.created_at DESC').limit(1)
joins("LEFT OUTER JOIN (#{case_query.to_sql}) cases ON cases.title_id = titles.id")
end
end
This way, you can chain the scope to others like so:
Title.where(attribute1: value1).case_joins("typeA")
(Note that removed the superfluous WHERE conditions in the outer SELECT.)

Answer 2

It's difficult to infer what the rest of your code looks like, but I presume titles is being used in a query further up your call stack.
If you were to use ActiveRecord instead of native SQL, you could do something like this:
def case_joins(scope, title_id, type)
ids = Case.where(title_id: title_id, value: 0, type: type)
.order('created_at desc').limit(1).pluck(:id)
scope.joins('left outer join cases on cases.title_id = titles.id')
.where(value: 0, type: type, id: ids)
end
scope here is the current AR query you are modifying.
This is off the top of my head, so I'm not sure if the AR syntax above is correct, but it does avoid the need to interpolate SQL and also uses scoping.
To be honest, though, it's not all that much more readable than native SQL, and so YMMV. It does at least mean that (apart from the join) you're not encoding SQL in your code.

Answer 3

Here is modification of #eirikir's answer, that works the same way as method in question.
def case_joins(type)
case_query = Case.from("cases c").where('c.title_id = titles.id AND c.value = 0 AND c.type = ?', type).order('c.created_at DESC').select(:id).limit(1)
"LEFT OUTER JOIN cases ON cases.title_id = titles.id AND cases.id = (#{case_query.to_sql})"
end