FEATURE: allow embedding based search without hyde (#777)

This allows callers of embedding based search to bypass hyde.

Hyde will expand the search term using an LLM, but if an LLM is
performing the search we can skip this expansion.

It also introduced some tests for the controller which we did not have

app/controllers/discourse_ai/embeddings/embeddings_controller.rb

@@ -9,6 +9,7 @@ module DiscourseAi
 
       def search
         query = params[:q].to_s
+        skip_hyde = params[:hyde].downcase.to_s == "false" || params[:hyde].to_s == "0"
 
         if query.length < SiteSetting.min_search_term_length
           raise Discourse::InvalidParameters.new(:q)
@@ -31,7 +32,7 @@ module DiscourseAi
 
         hijack do
           semantic_search
-            .search_for_topics(query)
+            .search_for_topics(query, _page = 1, hyde: !skip_hyde)
             .each { |topic_post| grouped_results.add(topic_post) }
 
           render_serialized(grouped_results, GroupedSearchResultSerializer, result: grouped_results)
@@ -39,6 +40,9 @@ module DiscourseAi
       end
 
       def quick_search
+        # this search function searches posts (vs: topics)
+        # it requires post embeddings and a reranker
+        # it will not perform a hyde expantion
         query = params[:q].to_s
 
         if query.length < SiteSetting.min_search_term_length

lib/embeddings/semantic_search.rb

@@ -11,6 +11,7 @@ module DiscourseAi
 
         Discourse.cache.delete(hyde_key)
         Discourse.cache.delete("#{hyde_key}-#{SiteSetting.ai_embeddings_model}")
+        Discourse.cache.delete("-#{SiteSetting.ai_embeddings_model}")
       end
 
       def initialize(guardian)
@@ -29,19 +30,14 @@ module DiscourseAi
         Discourse.cache.read(embedding_key).present?
       end
 
-      def search_for_topics(query, page = 1)
-        max_results_per_page = 100
-        limit = [Search.per_filter, max_results_per_page].min + 1
-        offset = (page - 1) * limit
-        search = Search.new(query, { guardian: guardian })
-        search_term = search.term
-
-        return [] if search_term.nil? || search_term.length < SiteSetting.min_search_term_length
-
-        strategy = DiscourseAi::Embeddings::Strategies::Truncation.new
-        vector_rep =
-          DiscourseAi::Embeddings::VectorRepresentations::Base.current_representation(strategy)
+      def vector_rep
+        @vector_rep ||=
+          DiscourseAi::Embeddings::VectorRepresentations::Base.current_representation(
+            DiscourseAi::Embeddings::Strategies::Truncation.new,
+          )
+      end
 
+      def hyde_embedding(search_term)
         digest = OpenSSL::Digest::SHA1.hexdigest(search_term)
         hyde_key = build_hyde_key(digest, SiteSetting.ai_embeddings_semantic_search_hyde_model)
 
@@ -57,14 +53,34 @@ module DiscourseAi
             .cache
             .fetch(hyde_key, expires_in: 1.week) { hypothetical_post_from(search_term) }
 
-        hypothetical_post_embedding =
         Discourse
           .cache
           .fetch(embedding_key, expires_in: 1.week) { vector_rep.vector_from(hypothetical_post) }
+      end
+
+      def embedding(search_term)
+        digest = OpenSSL::Digest::SHA1.hexdigest(search_term)
+        embedding_key = build_embedding_key(digest, "", SiteSetting.ai_embeddings_model)
+
+        Discourse
+          .cache
+          .fetch(embedding_key, expires_in: 1.week) { vector_rep.vector_from(search_term) }
+      end
+
+      def search_for_topics(query, page = 1, hyde: true)
+        max_results_per_page = 100
+        limit = [Search.per_filter, max_results_per_page].min + 1
+        offset = (page - 1) * limit
+        search = Search.new(query, { guardian: guardian })
+        search_term = search.term
+
+        return [] if search_term.nil? || search_term.length < SiteSetting.min_search_term_length
+
+        search_embedding = hyde ? hyde_embedding(search_term) : embedding(search_term)
 
         candidate_topic_ids =
           vector_rep.asymmetric_topics_similarity_search(
-            hypothetical_post_embedding,
+            search_embedding,
             limit: limit,
             offset: offset,
           )

spec/requests/embeddings/embeddings_controller_spec.rb

@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+describe DiscourseAi::Embeddings::EmbeddingsController do
+  context "when performing a topic search" do
+    before do
+      SiteSetting.min_search_term_length = 3
+      SiteSetting.ai_embeddings_model = "text-embedding-3-small"
+      DiscourseAi::Embeddings::SemanticSearch.clear_cache_for("test")
+      SearchIndexer.enable
+    end
+
+    fab!(:category)
+    fab!(:subcategory) { Fabricate(:category, parent_category_id: category.id) }
+
+    fab!(:topic)
+    fab!(:post) { Fabricate(:post, topic: topic) }
+
+    fab!(:topic_in_subcategory) { Fabricate(:topic, category: subcategory) }
+    fab!(:post_in_subcategory) { Fabricate(:post, topic: topic_in_subcategory) }
+
+    def index(topic)
+      strategy = DiscourseAi::Embeddings::Strategies::Truncation.new
+      vector_rep =
+        DiscourseAi::Embeddings::VectorRepresentations::Base.current_representation(strategy)
+
+      stub_request(:post, "https://api.openai.com/v1/embeddings").to_return(
+        status: 200,
+        body: JSON.dump({ data: [{ embedding: [0.1] * 1536 }] }),
+      )
+
+      vector_rep.generate_representation_from(topic)
+    end
+
+    def stub_embedding(query)
+      embedding = [0.049382] * 1536
+      EmbeddingsGenerationStubs.openai_service(SiteSetting.ai_embeddings_model, query, embedding)
+    end
+
+    it "returns results correctly when performing a non Hyde search" do
+      index(topic)
+      index(topic_in_subcategory)
+
+      query = "test"
+      stub_embedding(query)
+
+      get "/discourse-ai/embeddings/semantic-search.json?q=#{query}&hyde=false"
+
+      expect(response.status).to eq(200)
+      expect(response.parsed_body["topics"].map { |t| t["id"] }).to contain_exactly(
+        topic.id,
+        topic_in_subcategory.id,
+      )
+    end
+
+    it "is able to filter to a specific category (including sub categories)" do
+      index(topic)
+      index(topic_in_subcategory)
+
+      query = "test category:#{category.slug}"
+      stub_embedding("test")
+
+      get "/discourse-ai/embeddings/semantic-search.json?q=#{query}&hyde=false"
+
+      expect(response.status).to eq(200)
+      expect(response.parsed_body["topics"].map { |t| t["id"] }).to eq([topic_in_subcategory.id])
+    end
+  end
+end