pg_search: Using a dynamic method as the against parameter

Question

According to the accepted answer of this question, you should be able to use the return value of a instance method as the against parameter...

class Car < ActiveRecord::Base
  include PgSearch
  multisearchable :against => [:name, manufacturer_name]
  belongs_to :manufacturer

  def manufacturer_name
   manufacturer.name
  end
end

However, when I try to do this in a clean app (to rule out conflicting code in the real app) with the above model, db, etc created I get an undefined local variable or method error - what am I missing?

Answer 1

Ok, the short story is that the code provided in the linked post does not and cannot work as it would appear as though you cannot reference a method (instance or otherwise) in this way - which makes sense: the class needs to compile in order for the method to become available, but can't because it requires said method in order for compiling to be possible.

To achieve what I was originally attempting (without overriding pg_search) I took the following steps:

Firstly, the against declaration should use a symbol in place of the original method call.

multisearchable :against => [:name, :manufacturer_name]

This done, when an object is saved the PgSearch::Document will be created/updated using the manufacturer_name method. However, this will break if you attempt to rebuild the search index with the following error:

ActiveRecord::StatementInvalid: PG::UndefinedColumn: ERROR:  column cars.manufacturer_name does not exist
  LINE 5: ...sce("cars".name::text, '') || ' ' || coalesce("cars"...
                                                           ^
: INSERT INTO "pg_search_documents" (searchable_type, searchable_id, content, created_at, updated_at)
  SELECT 'Car' AS searchable_type,
         "cars".id AS searchable_id,
         (
           coalesce("cars".name::text, '') || ' ' || coalesce("cars".manufacturer_name::text, '')
         ) AS content,
         '2014-01-29 14:08:00.190767' AS created_at,
         '2014-01-29 14:08:00.190767' AS updated_at
  FROM "cars"

To fix this, override the rebuild_pg_search_documents class method which is added by the Multisearch module, to build a dynamic SQL insert query rather than reply on the existing pure SQL INSERT INTO table_name (columns) SELECT etc query:

def self.rebuild_pg_search_documents
  cars = Car.all

  query_str = 'INSERT INTO pg_search_documents (searchable_type, searchable_id, content, created_at, updated_at) VALUES'

  cars.each do |car|
    query_str += "('Car', #{car.id}, '#{car.name} #{car.manufacturer_name}', NOW(), NOW())"

    query_str += ', ' unless car == cars.last
  end

  query_str += ';'

  connection.execute query_str
end

Hopefully this will help someone else.