Complex Query in Rails using Model.where(…).includes(…)

Question

I am trying to query through four layers (yikes!) of associations. Associations are as follows:

(edit: added associations details, I had them in the source but didn't include them here)

Provider
   has_many :specialties, :through => :provider_specialties
   has_many :provider_specialties, :through => :provider_licenses
   has_many :provider_licenses

ProviderLicense
  belongs_to :provider
  has_many :specialties, :through => :provider_specialties
  has_many :provider_specialties

#linking model between ProviderLicense and Specialty
ProviderSpecialty
  belongs_to :provider_license
  belongs_to :specialty

Specialty
  has_many :provider_specialties

My starting point is Ryan Bates's RailsCast . I have had success in searching for associated objects one layer deep, but this one is killing me.

providers = Provider.includes([:provider_languages, { :provider_licenses => :provider_specialties }]).where(conditions)

def specialties_and_conditions
  ["providers_specialties.specialty_id = ?", specialty_id] unless specialty_id.blank?
end

(edit: working query and joins below)

Provider.joins([:specialties => { :provider_licenses => :provider_specialties }]).where(conditions)

def specialties_and_conditions
  ["specialty_id = ?", specialty_id] unless specialty_id.blank?
end

I don't really understand how the "includes" method works. I am trying to search for the specialty_id in the ProviderSpecialty (linking) relationship with the code above, but have had little success making it work. Any help would be greatly appreciated! Thanks!

Answer 1

It looks like you are confusing includes with joins. Includes is used to preload data to save on queries. Joins is used like a normal Join in SQL statements to let you filter by associated criteria.

First I would add this to your ProviderLicense model (this lets you use the many-to-many relationship easier):

has_many :specialties, :through => :provider_specialties

I don't really know what query you are trying to achieve, but maybe this will help?

Provider.joins({:provider_licenses => [:specialties]}).where('specialties.id = ?', specialty_id)

You should have a look in your development logs at the SQL query that is generated and then tweak from there.

I haven't tested my code, so it may be slightly off with syntax.