Custom Query Method approach

In this approach, the complex logic shown previously in the calling program is transferred to the domain service class in a custom method called salesReportByCountry() instead. As with the logic shown previously, first, we initialize the variables:

    def salesReportByCountry(self, year) :
        from bson.regex import Regex
        pattern = '^' + str(year)
        regex   = Regex(pattern)
        query   = dict({'dateOfPurchase':{'$regex':regex}})
        proj    = dict({'dateOfPurchase':1,'extendedPrice':1, \
                        'country':1,'_id':0})
        order   = [('country', 1),('dateOfPurchase', 1)]
        results = {}

We then implement exactly the same logic shown in the calling program prior:

        for doc in self.genericFetch(query, proj, order) :
            country = doc['country']
            dop     = doc['dateOfPurchase'...