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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 aggregate(self, query: Optional[dict] = None, group: Optional[dict] = None, order_by: Optional[tuple] = None) -> List[IModel]: """Get aggregated results : param query: Rulez based query : param group: Grouping structure : param order_by: Tuple of ``(field, order)`` where ``order`` is ``'asc'`` or ``'desc'`` : todo: Grouping structure need to be documented """

        raise NotImplementedError