Linq中的分组和左连接

Question

[有两个表，一个是customer的字段为customerID，GroupID，另一个是CustomerGroup的字段为GroupID，GroupName，我要获取每个组中customerID的数量，这是linq语句：

var groups = from customerGroups in db.CustomerGroup 
                         join customers in db.Customers on customerGroups.GroupID equals customers.GroupID into gc
                         where customerGroups.MerchantID == merchantID
                         from subCustomerGroups in gc.DefaultIfEmpty()
                         group customerGroups by customerGroups.GroupName into grpCustomerGroups
                         select new { GroupName = grpCustomerGroups.Key, Quantity = customers.CustomerID};

问题是Quantity = customers.CustomerID无效，如何更正该陈述？

Answer 1

实际上，您实际上需要使用Select语句对您的Group进行一些投影，然后调用Count方法，因此您需要这样的东西：

Quantity = grpCustomerGroups.Select(c => c.CustomerID).Count()

或者只是为了获得每个组的数量，您可以：

Quantity = grpCustomerGroups.Count()