clientSellDeferredThisMonth method
Implementation
num clientSellDeferredThisMonth(
    int herderId, DateTime dateMonthStart, DateTime dateMonthEnd) {
  return where((t) => t.status)
      .where((t) => t.contactId == herderId)
      .where((t) => t.date.isAfter(dateMonthStart))
      .where((t) => t.date.isBefore(dateMonthEnd))
      .where((t) => t.ticketType == TicketType.sellDeferred)
      .fold(0.0, (prev, e) => prev + e.totalPriceTaxAndPromoIncluded);
}