code: def check_database_connected(db):
      
      from sqlalchemy.exc import DBAPIError, SQLAlchemyError
  
      errors = []
      try:
          with db.engine.connect() as connection:
              connection.execute('SELECT 1;')
      except DBAPIError as e:
          msg = 'DB-API error: {!s}'.format(e)
          errors.append(Error(msg, id=health.ERROR_DB_API_EXCEPTION))
      except SQLAlchemyError as e:
          msg = 'Database misconfigured: "{!s}"'.format(e)
          errors.append(Error(msg, id=health.ERROR_SQLALCHEMY_EXCEPTION))
      return errors
docs: A built-in check to see if connecting to the configured default
      database backend succeeds.
  
      It's automatically added to the list of Dockerflow checks if a
      :class:`~flask_sqlalchemy.SQLAlchemy` object is passed
      to the :class:`~dockerflow.flask.app.Dockerflow` class during
      instantiation, e.g.::
  
          from flask import Flask
          from flask_sqlalchemy import SQLAlchemy
          from dockerflow.flask import Dockerflow
  
          app = Flask(__name__)
          app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////tmp/test.db'
          db = SQLAlchemy(app)
  
          dockerflow = Dockerflow(app, db=db)