Support encrypted attributes on columns with default values

Before, it was failing to read these columns because their contents
were not encrypted, unless you enabled `config.active_record.encryption.support_unencrypted_data`.

Now, it will detect the change at creation time for these records and
effectively encrypt those values, preventing the problem.

Fixes #44314 #43664
Closes #44993

Co-authored-by: Dima Fatko <fatkodima123@gmail.com>

activerecord/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Support encrypted attributes on columns with default db values.
+
+This adds support for encrypted attributes defined on columns with default values. 
+It will encrypt those values at creation time. Before, it would raise an
+error unless `config.active_record.encryption.support_unencrypted_data` was true.
+
+*Jorge Manrubia* and *Dima Fatko*
+
 *   Allow overriding `reading_request?` in `DatabaseSelector::Resolver`
 
     The default implementation checks if a request is a `get?` or `head?`,

activerecord/lib/active_record/encryption/encryptable_record.rb

@@ -82,7 +82,7 @@ def global_previous_schemes_for(scheme)
           def encrypt_attribute(name, attribute_scheme)
             encrypted_attributes << name.to_sym
 
-            attribute name do |cast_type|
+            attribute name, default: -> { columns_hash[name.to_s]&.default } do |cast_type|
               ActiveRecord::Encryption::EncryptedAttributeType.new scheme: attribute_scheme, cast_type: cast_type
             end
 

activerecord/lib/active_record/encryption/encrypted_attribute_type.rb

@@ -40,7 +40,7 @@ def serialize(value)
       end
 
       def changed_in_place?(raw_old_value, new_value)
-        old_value = raw_old_value.nil? ? nil : deserialize(raw_old_value)
+        old_value = raw_old_value.nil? ? nil : deserialize_previous_value_to_determine_change(raw_old_value)
         old_value != new_value
       end
 
@@ -135,6 +135,14 @@ def decryption_options
         def clean_text_scheme
           @clean_text_scheme ||= ActiveRecord::Encryption::Scheme.new(downcase: downcase?, encryptor: ActiveRecord::Encryption::NullEncryptor.new)
         end
+
+        def deserialize_previous_value_to_determine_change(raw_old_value)
+          deserialize(raw_old_value)
+          # We tolerate unencrypted data when determining if a column changed
+          # to support default DB values in encrypted attributes
+        rescue ActiveRecord::Encryption::Errors::Decryption
+          nil
+        end
     end
   end
 end

activerecord/test/cases/encryption/encryptable_record_test.rb

@@ -292,6 +292,11 @@ def name
     assert_equal Encoding::US_ASCII, book.reload.name.encoding
   end
 
+  test "support encrypted attributes defined on columns with default values" do
+    book = EncryptedBook.create!
+    assert_encrypted_attribute(book, :name, "<untitled>")
+  end
+
   private
     class FailingKeyProvider
       def decryption_key(message) end

activerecord/test/schema/schema.rb

@@ -141,7 +141,7 @@
   create_table :encrypted_books, id: :integer, force: true do |t|
     t.references :author
     t.string :format
-    t.column :name, :string
+    t.column :name, :string, default: "<untitled>"
     t.column :original_name, :string
 
     t.datetime :created_at