ThinkingSphinx: association field UPDATE does not reindex - ruby-on-rails

Question

thinking-sphinx (3.3.0)
Rails 5.0.4
I have troubles with updating associations - ThinkingSphinx (apparently) does not reindex them.
model1
class DocRequest < ApplicationRecord
has_many :doc_responses, :inverse_of => :doc_request, dependent: :destroy
end
model2
class DocResponse < ApplicationRecord
belongs_to :doc_request, :inverse_of => :doc_responses
end
app/indices/doc_response_index.rb
ThinkingSphinx::Index.define :doc_response, :with => :active_record, :delta => true do
indexes doc_request.title, :as => :doc_request_title, :sortable => true
indexes text
has doc_request_id
end
Controller:
result = DocResponse.search #keyword
When I update the title of a DocRequest model (in Admin area), ThinkingSphinx obviously does not reindex the doc_request.title field, e.g. the result = DocResponse.search #keyword query doesn't change.
What's wrong?
Running rake ts:rebuild solves the problem. But I can't do it on every update.
I tried to add a
ThinkingSphinx::Index.define :doc_request, :with => :active_record, :delta => true do
indexes title
end
index and then to perform directly result = DocRequest.search #keyword - it worked correctly. But that's surely not what I need.
db/schema.rb
create_table "doc_requests", force: :cascade do |t|
t.string "title"
t.text "text"
t.boolean "paid"
t.integer "user_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.boolean "delta", default: true, null: false
t.index ["user_id"], name: "index_doc_requests_on_user_id", using: :btree
end
create_table "doc_responses", force: :cascade do |t|
t.boolean "chosen"
t.text "text"
t.float "price"
t.integer "user_id"
t.integer "doc_request_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.boolean "delta", default: true, null: false
t.index ["doc_request_id"], name: "index_doc_responses_on_doc_request_id", using: :btree
t.index ["user_id"], name: "index_doc_responses_on_user_id", using: :btree
end
What did I do wrong? I need some help.
Can I enable some verbose console mode in ThinkingSphinx - to see the reindexing events while updating? That might be useful for debugging.
I quess that the answer is somewhere near this http://freelancing-gods.com/thinking-sphinx/deltas.html#deltas-and-associations , but what exactly to do - I don't know.

Answer 1

Thinking Sphinx does not automatically detect your associations and how they relate to your indexed data whenever you make an update to your models, as that could potentially be very complex (and thus, slow).
You've linked to the exactly correct part of the documentation, though it's slightly out of date - you'll want to use after_commit instead. Whenever you have a DocRequest updating, you'll want to set the delta flags for all of the associated DocResponse objects:
class DocRequest < ActiveRecord::Base
# ...
after_commit :set_response_delta_flags
# ...
private
def set_response_delta_flags
doc_responses.each { |response|
response.update_attributes :delta => true
}
end
# ...
end
Updating each response will fire off the delta processing for the affected response objects, which will in turn ensure their Sphinx data is up-to-date.