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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_fields_for_model(model):
 """ Gets all of the fields on the model. :param DeclarativeModel model: A SQLAlchemy ORM Model :return: A tuple of the fields on the Model corresponding to the columns on the Model. :rtype: tuple """

    fields = []
    for name in model._sa_class_manager:
        prop = getattr(model, name)
        if isinstance(prop.property, RelationshipProperty):
            for pk in prop.property.mapper.primary_key:
                fields.append('{0}.{1}'.format(name, pk.name))
        else:
            fields.append(name)
    return tuple(fields)