changes poll_voters to optionally reference an answer

adds indexes for poll_voters

db/migrate/20170125114952_add_answer_id_to_poll_voters.rb

@@ -0,0 +1,9 @@
+class AddAnswerIdToPollVoters < ActiveRecord::Migration
+  def change
+    add_column :poll_voters, :answer_id, :integer, default: nil
+
+    add_index :poll_voters, :document_number
+    add_index :poll_voters, :poll_id
+    add_index :poll_voters, [:poll_id, :document_number, :document_type], name: 'doc_by_poll'
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170125112017) do
+ActiveRecord::Schema.define(version: 20170125114952) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -468,8 +468,13 @@ ActiveRecord::Schema.define(version: 20170125112017) do
     t.integer  "age"
     t.string   "gender"
     t.integer  "geozone_id"
+    t.integer  "answer_id"
   end
 
+  add_index "poll_voters", ["document_number"], name: "index_poll_voters_on_document_number", using: :btree
+  add_index "poll_voters", ["poll_id", "document_number", "document_type"], name: "doc_by_poll", using: :btree
+  add_index "poll_voters", ["poll_id"], name: "index_poll_voters_on_poll_id", using: :btree
+
   create_table "polls", force: :cascade do |t|
     t.string   "name"
     t.datetime "starts_at"