code: def init_app(self, app):
          
          app.extensions = getattr(app, "extensions", {})
  
          # If using Flask-SQLAlchemy, attach db.session to ModelSchema
          if has_sqla and "sqlalchemy" in app.extensions:
              db = app.extensions["sqlalchemy"].db
              self.ModelSchema.OPTIONS_CLASS.session = db.session
          app.extensions[EXTENSION_NAME] = self
docs: Initializes the application with the extension.
  
          :param Flask app: The Flask application object.