左外连接c#的结果失败

Question

我想在两个查询之间进行左外连接并将结果填充到新的对象实例中

这是第一个查询的代码，单独工作正常，获取数据

 var finances = _context.Finances
            .GroupBy(p => p.CustomerID)
            .Select(m => new 
            {
                CustomerID = m.Key,
                Debtor = m.Sum(p => p.Debtor),
                Creditor = m.Sum(p => p.Creditor),
            }).ToList();

第二个查询单独工作正常，获取数据

          var events = _context.Events
            .Include(p=>p.Customer)
            .Where(p=>p.Start.ToString().CompareTo(reqDate) >= 0)
            .Select(p => new 
            {
                CustomerID = p.CustomerID,
                FullName =p.Customer.FirstName + ' ' +p.Customer.LastName,
                End =p.End,
                Start = p.Start,                    
            }).ToList();

所以左外连接应该是这样的

          var qry = events.GroupJoin(
              finances,
              ev1 => ev1.CustomerID,
              fi1 => fi1.CustomerID,
              (f, bs) => new { events = f, finances = bs })
          .SelectMany(
              eventsFinances => eventsFinances.finances.DefaultIfEmpty(),
              (x, y) => new RequestEventsDto
              {
                  CustomerID=x.events.CustomerID,
                  Start = x.events.Start,
                  End = x.events.End,
                  FullName = x.events.FullName,
                  Debtor = y.Debtor,
                  Creditor = y.Creditor,
              });

事件表将填充数据，但财务表不会（其中实际包含数据）并给出此错误

“对象引用未设置为对象的实例。”

如果我在财务表中评论这两行，其余的都可以正常工作

Debtor = y.Debtor,
Creditor = y.Creditor,

左外连接的哪一部分有问题？

Answer 1

试试这个

var var qry = from e in events
            join  f in finances on e.CustomerID equals f.CustomerID into fj
            from f in fj.DefaultIfEmpty()
             select new {
                  CustomerID=e.CustomerID,
                  Start =e.Start,
                  End = e.End,
                  FullName = e.FullName,
                  Debtor = f.Debtor,
                  Creditor = f.Creditor
                 };