LINQ子查询

Question

我需要对数据库表（Period）的时间段和表（发票）中的发票列表执行LINQ查询，这些发票列在期间的开始和结束日期之内。这两个表之间没有关键引用，如何进行Invoice子查询？

我正在尝试做类似以下的事情：

var query = (from p in db.DataContext.Periods
             // Subquery i in db.DataContext.Invoices
             let InvoiceAmount = i.Where(t => t.InvoiceDate >= p.StartDate && t.InvoiceDate <= p.EndDate)
             select new PeriodView
             (
                p.Name,
                p.StartDate,
                p.EndDate,
                InvoiceAmount.Count()
              ));

Answer 1

var periodViewList = 
    (from p in db.DataContext.Periods
    select new PeriodView(
      p.Name,
      p.StartDate,
      p.EndDate,
      db.DataContext.Invoices.Where(i => i.InvoiceDate >= p.StartDate && i.InvoiceDate <= p.EndDate).Count()
    )).ToList();

我假设PeriodView构造函数看起来像这样

public PeriodView (string name, DateTime startDate, DateTime endDate, int invoiceCount) {
...
}