Auto default for UUID primary keys

Patch load_schmema! to set the default value for UUID primary keys. This
removes the need to patch ApplicationRecord + Rails models individually.

It also means we no longer need to patch the default in for the integer
primary key in Search::Record::SQLite.

app/models/application_record.rb

@@ -2,6 +2,4 @@ class ApplicationRecord < ActiveRecord::Base
   primary_abstract_class
 
   configure_replica_connections
-
-  attribute :id, :uuid, default: -> { ActiveRecord::Type::Uuid.generate }
 end

app/models/search/record/sqlite.rb

@@ -2,8 +2,6 @@ module Search::Record::SQLite
   extend ActiveSupport::Concern
 
   included do
-    # Override default UUID id attribute, as FTS5 uses rowid integer primary key
-    attribute :id, :integer, default: nil
     attribute :result_title, :string
     attribute :result_content, :string
 

config/initializers/uuid_framework_models.rb

@@ -1,14 +1,10 @@
-# Inject UUID primary key support into Rails framework models
+# Inject account associations into Rails framework models
 Rails.application.config.to_prepare do
-  ActionText::RichText.attribute :id, :uuid, default: -> { ActiveRecord::Type::Uuid.generate }
   ActionText::RichText.belongs_to :account, default: -> { record.account }
 
-  ActiveStorage::Attachment.attribute :id, :uuid, default: -> { ActiveRecord::Type::Uuid.generate }
   ActiveStorage::Attachment.belongs_to :account, default: -> { record.account }
 
-  ActiveStorage::Blob.attribute :id, :uuid, default: -> { ActiveRecord::Type::Uuid.generate }
   ActiveStorage::Blob.belongs_to :account, default: -> { Current.account }
 
-  ActiveStorage::VariantRecord.attribute :id, :uuid, default: -> { ActiveRecord::Type::Uuid.generate }
   ActiveStorage::VariantRecord.belongs_to :account, default: -> { blob.account }
 end

config/initializers/uuid_primary_keys.rb

@@ -1,4 +1,30 @@
-# Automatically use UUID type for all binary(16) columns
+# Automatically use UUID type for all binary(16) columns and generate defaults
+
+module UuidPrimaryKeyDefault
+  def load_schema!
+    define_uuid_primary_key_pending_default
+    super
+  end
+
+  private
+    def define_uuid_primary_key_pending_default
+      if uuid_primary_key?
+        pending_attribute_modifications << PendingUuidDefault.new(primary_key)
+      end
+    rescue ActiveRecord::StatementInvalid
+      # Table doesn't exist yet
+    end
+
+    def uuid_primary_key?
+      table_name && primary_key && schema_cache.columns_hash(table_name)[primary_key]&.type == :uuid
+    end
+
+    PendingUuidDefault = Struct.new(:name) do
+      def apply_to(attribute_set)
+        attribute_set[name] = attribute_set[name].with_user_default(-> { ActiveRecord::Type::Uuid.generate })
+      end
+    end
+end
 
 module MysqlUuidAdapter
   extend ActiveSupport::Concern
@@ -12,6 +38,20 @@ module MysqlUuidAdapter
     end
   end
 
+  # Override fetch_type_metadata to preserve UUID type and limit
+  def fetch_type_metadata(sql_type, extra = "")
+    if sql_type == "binary(16)"
+      simple_type = ActiveRecord::ConnectionAdapters::SqlTypeMetadata.new(
+        sql_type: sql_type,
+        type: :uuid,
+        limit: 16
+      )
+      ActiveRecord::ConnectionAdapters::MySQL::TypeMetadata.new(simple_type, extra: extra)
+    else
+      super
+    end
+  end
+
   class_methods do
     def native_database_types
       @native_database_types_with_uuid ||= super.merge(uuid: { name: "binary", limit: 16 })
@@ -69,6 +109,7 @@ module TableDefinitionUuidSupport
 end
 
 ActiveSupport.on_load(:active_record) do
+  ActiveRecord::Base.singleton_class.prepend(UuidPrimaryKeyDefault)
   ActiveRecord::ConnectionAdapters::TableDefinition.prepend(TableDefinitionUuidSupport)
 end