Sync transaction state when accessing primary key

If a record is modified inside a transaction, it must check the outcome
of that transaction before accessing any state which would no longer be
valid if it was rolled back.

For example, consider a new record that was saved inside a transaction
which was later rolled back: it should be restored to its previous state
so that saving it again inserts a new row into the database instead of
trying to update a row that no longer exists.

The `id` and `id=` methods defined on the PrimaryKey module implement
this correctly, but when a model uses a custom primary key, the reader
and writer methods for that attribute must check the transaction state
too. The `read_attribute` and `write_attribute` methods also need to
check the transaction state when accessing the primary key.

2 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index fdc4bf6621..f7f3b7ec96 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -29,9 +29,11 @@ module ActiveRecord
             temp_method = "__temp__#{safe_name}"
 
             ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
+            sync_with_transaction_state = "sync_with_transaction_state" if name == primary_key
 
             generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
               def #{temp_method}
+                #{sync_with_transaction_state}
                 name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
                 _read_attribute(name) { |n| missing_attribute(n, caller) }
               end
@@ -55,6 +57,7 @@ module ActiveRecord
         end
 
         name = self.class.primary_key if name == "id".freeze && self.class.primary_key
+        sync_with_transaction_state if name == self.class.primary_key
         _read_attribute(name, &block)
       end
 
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index 54b673c72e..9c43567a11 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -13,10 +13,12 @@ module ActiveRecord
           def define_method_attribute=(name)
             safe_name = name.unpack("h*".freeze).first
             ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
+            sync_with_transaction_state = "sync_with_transaction_state" if name == primary_key
 
             generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
               def __temp__#{safe_name}=(value)
                 name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
+                #{sync_with_transaction_state}
                 _write_attribute(name, value)
               end
               alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
@@ -36,6 +38,7 @@ module ActiveRecord
         end
 
         name = self.class.primary_key if name == "id".freeze && self.class.primary_key
+        sync_with_transaction_state if name == self.class.primary_key
         _write_attribute(name, value)
       end