def get_variants(self, chromosome=None, start=None, end=None):
        """Return all variants in the database
        If no region is specified all variants will be returned.

        Args:
            chromosome(str)
            start(int)
            end(int)
        
    
        Returns:
            variants(Iterable(Variant))
        """
        query = {}
        if chromosome:
            query['chrom'] = chromosome
        if start:
            query['start'] = {'$lte': end}
            query['end'] = {'$gte': start}
        LOG.info("Find all variants {}".format(query))
        return self.db.variant.find(query).sort([('start', ASCENDING)])
Return all variants in the database
        If no region is specified all variants will be returned.

        Args:
            chromosome(str)
            start(int)
            end(int)
        
    
        Returns:
            variants(Iterable(Variant))