linq表达式 多表关联查询，左连接查询

多表关联查询

　　　　　　　　　　　　　from x in _wholesalerReplenishmentDetailRepository.GetAll()
                      join n in _wholesalerReplenishmentRepository.GetAll() on x.WholesalerReplenishmentId equals n.Id  //批发商补货
                      join y in _store.GetAll() on x.StoreId equals y.Id //店铺
                      join z in _wholesalerEmployeeRepository.GetAll() on x.EmployeeId equals z.Id into groupsz
                      from grpz in groupsz.DefaultIfEmpty() //业务员（可能为空）
                      join m in _wholesalerRepository.GetAll() on x.WholesalerId equals m.Id into groupsm
                      from grpm in groupsm.DefaultIfEmpty() //批发商（可能为空）
                      orderby x.CreationTime descending
                      select new WholesalerReplenishmentFullDto
                      {
                          Id = x.Id,
                          CompanyName = grpm.CompanyName,
                          EmployeeName = x.EmployeeId == null ? grpm.ContactPerson : grpz.EmployeeName,//可能批发商自己补货,//可能批发商自己补货,
                          StoreName = y.Name,
                          StoreBossName = y.BossName,
                          CreatTime = x.CreationTime,
                          CreationAddress = n.CreationAddress,
                          OpratorId = x.LastModifierUserId == null ? x.CreatorUserId : x.LastModifierUserId,
                          OpratorTime = x.LastModificationTime == null ? x.CreationTime : x.LastModificationTime,
                          ProductId = x.ProductId
                      };

let设置临时条件

　　　　　　　　　 from u in users
         　　　　let number = Int32.Parse(u.Username.Substring(u.Username.Length - 1))
         　　　　where u.ID < 9 && number % 2 == 0
         　　　　select u