Question

我正在尝试使用Linq to SQL来进行完全外连接。我有一个基本的例子，但是当完全外连接的每一边都是从另一个内连接生成时，它不起作用。下面是代码。我意识到这可能会被放入更少的查询 - 但我宁愿将它们分开以使它们尽可能可读。在这种情况下，性能不是问题。

var productIds = db.OrderItemsIncoming.Select(i => i.ProductID)
    .Union(db.OrderItemsOutgoing.Select(o => o.ProductID))
    .Distinct();

var ordersIn =  from o in db.OrdersIncoming
                join i in db.OrderItemsIncoming on o.OrderNumber equals i.OrderNumber
                select new { o, i };

var ordersOut = from o in db.OrdersOutgoing
                join i in db.OrderItemsOutgoing on o.OrderNumber equals i.OrderNumber
                select new { o, i };

var fullOuterJoinResults =  from i in ordersIn
                            join o in ordersOut on i.i.ProductID equals o.i.ProductID into t
                            from o in t.DefaultIfEmpty()
                            where i == null ^ o == null
                            select new { i, o };

在我的测试中，ordersIn结果为空，ordersOut结果中有一行。所以我希望最终的fullOuterJoinResults有一行，但它是空的。

Answer 1

我发帖后的第二秒，我注意到一个错误，我没有在任何地方使用productID结果！： - /我将使用我的修复程序编辑这篇文章，一旦我完成它......

[编辑]

好的，这似乎有效：

var ordersIn =  from o in db.OrdersIncoming
                join i in db.OrderItemsIncoming on o.OrderNumber equals i.OrderNumber
                select new { o, i };

var ordersOut = from o in db.OrdersOutgoing
                join i in db.OrderItemsOutgoing on o.OrderNumber equals i.OrderNumber
                select new { o, i };

var productIds = db.OrderItemsIncoming.Select(i => i.ProductID)
    .Union(db.OrderItemsOutgoing.Select(o => o.ProductID))
    .Distinct();

var fullOuterJoinResults =    from pid in productIDs
                        join i in ordersIn on pid equals i.i.ProductID into t1
                        from i in t1.DefaultIfEmpty()
                        join o in ordersOut on pid equals o.i.ProductID into t2
                        from o in t2.DefaultIfEmpty()
                        where i == null ^ o == null
                        select new { i, o };

全外连接 - Linq To SQL

1 个答案: