@classmethod
def has_attr(cls, attr_name):
    """Check to see if an attribute is defined for the model."""
    if attr_name in cls.attrs:
        return True
    if isinstance(cls.primary_key_name, str
        ) and cls.primary_key_name == attr_name:
        return True
    if isinstance(cls.primary_key_name, tuple
        ) and attr_name in cls.primary_key_name:
        return True
    if cls.timestamps is not None and attr_name in cls.timestamps:
        return True
    return False
