`ActiveRecord::SchemaMigration` has no primary key.

Before this patch, using `ActiveRecord::Base.primary_key_prefix_type`
with `:table_name_with_underscore` would change the `SchemaMigration` model
to have a primary key. This resulted in broken queries for PG because it tried
to return the inserted PK (which does not exist).

Closes #15051.
Closes #15419.

1 files changed, 14 insertions, 0 deletions

diff --git a/activerecord/test/cases/ar_schema_test.rb b/activerecord/test/cases/ar_schema_test.rb
index 7290cd53b1..8700b20dee 100644
--- a/activerecord/test/cases/ar_schema_test.rb
+++ b/activerecord/test/cases/ar_schema_test.rb
@@ -17,6 +17,20 @@ if ActiveRecord::Base.connection.supports_migrations?
       ActiveRecord::SchemaMigration.delete_all rescue nil
     end
 
+    def test_has_no_primary_key
+      old_primary_key_prefix_type = ActiveRecord::Base.primary_key_prefix_type
+      ActiveRecord::Base.primary_key_prefix_type = :table_name_with_underscore
+      assert_nil ActiveRecord::SchemaMigration.primary_key
+
+      ActiveRecord::SchemaMigration.create_table
+      assert_difference "ActiveRecord::SchemaMigration.count", 1 do
+        ActiveRecord::SchemaMigration.create version: 12
+      end
+    ensure
+      ActiveRecord::SchemaMigration.drop_table
+      ActiveRecord::Base.primary_key_prefix_type = old_primary_key_prefix_type
+    end
+
     def test_schema_define
       ActiveRecord::Schema.define(:version => 7) do
         create_table :fruits do |t|