Merge pull request #4976 from kreynolds/fix_eager_without_pkey

Fix eagerly loading associations without primary keys

activerecord/lib/active_record/associations/join_dependency/join_part.rb

@@ -54,7 +54,7 @@ def column_names_with_alias
           unless @column_names_with_alias
             @column_names_with_alias = []
 
-            ([primary_key] + (column_names - [primary_key])).each_with_index do |column_name, i|
+            ([primary_key] + (column_names - [primary_key])).compact.each_with_index do |column_name, i|
               @column_names_with_alias << [column_name, "#{aliased_prefix}_r#{i}"]
             end
           end

activerecord/test/cases/associations/join_dependency_test.rb

+require "cases/helper"
+require 'models/edge'
+
+class JoinDependencyTest < ActiveRecord::TestCase
+  def test_column_names_with_alias_handles_nil_primary_key
+    assert_equal Edge.column_names, ActiveRecord::Associations::JoinDependency::JoinBase.new(Edge).column_names_with_alias.map(&:first)
+  end
+end
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