handle passing in primary key to unique_by, and handle primary keys missing indexes

activerecord/lib/active_record/insert_all.rb

@@ -14,7 +14,7 @@ module ActiveRecord
       @returning = (connection.supports_insert_returning? ? primary_keys : false) if @returning.nil?
       @returning = false if @returning == []
 
-      @unique_by = find_unique_index_for(unique_by) if unique_by
+      @unique_by = find_unique_index_for(unique_by || model.primary_key)
       @on_duplicate = :skip if @on_duplicate == :update && updatable_columns.empty?
 
       ensure_valid_options_for_connection!
@@ -32,7 +32,7 @@ module ActiveRecord
     end
 
     def primary_keys
-      Array(model.primary_key)
+      Array(connection.schema_cache.primary_keys(model.table_name))
     end
 
 
@@ -61,6 +61,8 @@ module ActiveRecord
 
         if index = unique_indexes.find { |i| match.include?(i.name) || i.columns == match }
           index
+        elsif match == primary_keys
+          nil
         else
           raise ArgumentError, "No unique index found for #{unique_by}"
         end

activerecord/test/cases/insert_all_test.rb

@@ -2,6 +2,7 @@
 
 require "cases/helper"
 require "models/book"
+require "models/speedometer"
 
 class ReadonlyNameBook < Book
   attr_readonly :name
@@ -225,6 +226,23 @@ class InsertAllTest < ActiveRecord::TestCase
     assert_equal new_name, Book.find(1).name
   end
 
+  def test_upsert_all_updates_existing_record_by_primary_key
+    skip unless supports_insert_on_duplicate_update?
+
+    Book.upsert_all [{ id: 1, name: "New edition" }], unique_by: :id
+
+    assert_equal "New edition", Book.find(1).name
+  end
+
+  def test_upsert_all_updates_existing_record_by_configured_primary_key
+    skip unless supports_insert_on_duplicate_update?
+
+    error = assert_raises ArgumentError do
+      Speedometer.upsert_all [{ speedometer_id: "s1", name: "New Speedometer" }]
+    end
+    assert_match "No unique index found for speedometer_id", error.message
+  end
+
   def test_upsert_all_does_not_update_readonly_attributes
     skip unless supports_insert_on_duplicate_update?