Fix tag search order and not to use tsvector (#3611)

* Sort results by the name
* Switch search method to simple `LIKE` matching instead of tsvector/tsquery

Previously we used scores from ts_rank_cd() to sort results, but it didn't work
because the function returns same score for all results. It's not for calculate
similarity of single words. Sometimes this bug even push out exact matching tag
from results.

Additionally, PostgreSQL supports prefix searching with standard btree index.
Using it offers simpler code, but also less index size and some speed.

diff --git a/app/models/tag.rb b/app/models/tag.rb
index 4001e6ed57a7edd8cf961f7ec60783a18d6484cf..08e3c1b03f0e845b90cfdcbf12607f2a8e3ecb82 100644 (file)
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -21,22 +21,9 @@ class Tag < ApplicationRecord
   end
 
   class << self
-    def search_for(terms, limit = 5)
-      terms      = Arel.sql(connection.quote(terms.gsub(/['?\\:]/, ' ')))
-      textsearch = 'to_tsvector(\'simple\', tags.name)'
-      query      = 'to_tsquery(\'simple\', \'\'\' \' || ' + terms + ' || \' \'\'\' || \':*\')'
-
-      sql = <<-SQL.squish
-        SELECT
-          tags.*,
-          ts_rank_cd(#{textsearch}, #{query}) AS rank
-        FROM tags
-        WHERE #{query} @@ #{textsearch}
-        ORDER BY rank DESC
-        LIMIT ?
-      SQL
-
-      Tag.find_by_sql([sql, limit])
+    def search_for(term, limit = 5)
+      pattern = sanitize_sql_like(term) + '%'
+      Tag.where('name like ?', pattern).order(:name).limit(limit)
     end
   end
 end

diff --git a/db/migrate/20170606113804_change_tag_search_index_to_btree.rb b/db/migrate/20170606113804_change_tag_search_index_to_btree.rb
new file mode 100644 (file)
index 0000000..5248e17
--- /dev/null
+++ b/db/migrate/20170606113804_change_tag_search_index_to_btree.rb
@@ -0,0 +1,12 @@
+class ChangeTagSearchIndexToBtree < ActiveRecord::Migration[5.1]
+
+  def up
+    remove_index :tags, name: :hashtag_search_index
+    execute 'CREATE INDEX hashtag_search_index ON tags (name text_pattern_ops);'
+  end
+
+  def down
+    remove_index :tags, name: :hashtag_search_index
+    execute 'CREATE INDEX hashtag_search_index ON tags USING gin(to_tsvector(\'simple\', tags.name));'
+  end
+end

diff --git a/db/schema.rb b/db/schema.rb
index ca904569e47fffbbf4d1abb96383766b0585756d..712f62ea6898d14342169f49a5054b8cf93e67b7 100644 (file)
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170604144747) do
+ActiveRecord::Schema.define(version: 20170606113804) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -320,7 +320,7 @@ ActiveRecord::Schema.define(version: 20170604144747) do
     t.string "name", default: "", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.index "to_tsvector('simple'::regconfig, (name)::text)", name: "hashtag_search_index", using: :gin
+    t.index "name text_pattern_ops", name: "hashtag_search_index"
     t.index ["name"], name: "index_tags_on_name", unique: true
   end
 

diff --git a/spec/models/tag_spec.rb b/spec/models/tag_spec.rb
index 7a5b8ec897558e9f40a2b5b386778d5a721dd1c5..2496946cbec405249fd5343233ed97bda01a2460 100644 (file)
--- a/spec/models/tag_spec.rb
+++ b/spec/models/tag_spec.rb
@@ -22,5 +22,14 @@ RSpec.describe Tag, type: :model do
 
       expect(results).to eq [tag]
     end
+
+    it 'finds the exact matching tag as the first item' do
+      similar_tag = Fabricate(:tag, name: "matchlater")
+      tag = Fabricate(:tag, name: "match")
+
+      results = Tag.search_for("match")
+
+      expect(results).to eq [tag, similar_tag]
+    end
   end
 end