Hi Tyler,
On Thu, Aug 9, 2012 at 2:32 PM, t.pickett66 <[email protected]> wrote:
> I have several models that are all linked together in a time
> tracking/billing system ala:
>
> class Claim < AR::B
> has_many :appointments
>
> def student
> @student ||= Student.joins(student_appointments:
> :claim).where('`claims`.`id` = ?',self.id).group('`students`.`id`').first
> #second draft
> # @student ||= (student_appointments.size == 0 ? nil :
> student_appointments[0].student) #first draft
> end
> end
>
>
> class Appointment < AR::B
> belongs_to :claim
> belongs_to :student
> end
>
>
> class Student < AR::B
> has_many :appointments
> end
>
> My users that administer these accounts want to be able to look at claims
> in the index but need to know who these claims were for. My first attempt
> building the view resulted in 2*N + 1 queries for getting the student's
> name, the second implementation paired that down to N+1 but obviously that
> still sucks. To totally avert the N+1 query problem typically I'd just
> eager load what I needed via Claim.includes(:appointments => :student) but
> I'd really like to avoid this here since I'll never actually use the
> appointments in the view. I've tried a has_one :through but rails doesn't
> allow a collection to then point at a single record this way, I've also
> tried just loading them via: Student.joins('join through to
> claims').where(claims.id in (?),claims.map(&:id)) in the
> presenter/controller but since everything is lazy loaded the query never
> gets executed and then the N+1 loads start. The third though I had was
> doing a belongs_to with conditions but there isn't any way to include
> joins in there so that's out. My last thought is to do something like:
>
> class Claim < AR::B
> has_many :appointments
> has_one :appointment
> has_one :student, :through => :appointment
> end
>
> but that clutters up the methods and would leave us open to the mistake of
> looking for the collection and getting the single. Are there any
> suggestions out there aside from loading the whole tree?
>
>
>
If it were me, I'd get rid of the student method and just put a has_many
and belongs_to relationship directly between Student and Claim. You can
have both that and the relationship through Appointment.
HTH,
Bill
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