docs: def get_data_source(query):
      """ Get data source connection metadata based on config. Prefer, in order:
          - Query file frontmatter
          - `db.yaml` file in query subdirectory
          - DATABASE_URL in environment
  
      To allow for possible non-SQL sources to be contributed, we only
      return a config value here, and leave connecting to concrete
      resultset module, as required values and connection method might change.
      (This is also why we return a dict, despite having a single value in the
      SQL case.)
      """
      # *** GET CONNECTION PARAMS: ***
      # from frontmatter
      try:
          return query.metadata['data_source']
      except KeyError:
          try:
              return dict(url=query.metadata['database_url'])
          except KeyError:
              pass
  
      # from file in directory if present
      db_file = query.path.parent / 'db.yaml'
      if db_file.is_file():
          with open(db_file, 'r') as dbf:
              db_meta = yaml.safe_load(dbf.read())
              try:
                  return db_meta['data_source']
              except KeyError:
                  try:
                      return dict(url=db_meta['database_url'])
                  except KeyError:
                      pass
  
      # Use env['DATABASE_URL']/sqlite if nothing else is configured
      return dict(
          url=os.getenv('DATABASE_URL', 'sqlite:///'))