如何在 Linq 中执行左外连接？ [复制]

Question

我是 Linq 新手，我需要将此查询转换为 DocumentStores 和 Orders 之间的左外连接，因为并非所有文档都与订单相关：

    var documents=(from d in _dataContextOrders .DocumentStores 
                           join o in _dataContextOrders.Orders on d.OrderID equals o.ID
                           join t in _dataContextOrders .DocumentTypes on d.DocumentType equals t.DocTypeID
                       select new
                           {
                               d.ID,
                               o.PORef ,
                               t.DocTypeDescription,
                               d.Name,
                               d.ContentType
                           }).ToList();

我如何做到这一点？

Answer 1

from a in dataContext.<tableA>
join _b in dataContext.<tableB> on a.id equals _b.aid into _b
from b in _b.DefaultIfEmpty()
select <whatyouwanttoselect>

如果 id 上的连接失败，b 将为空