从 lambda 查询结果访问关联时出现问题

发布于 2024-09-15 10:50:51 字数 939 浏览 3 评论 0原文

当您的子记录通过 lambda 查询加载时，是否有人在使用 LINQ to SQL 加载关联时遇到问题？例如：

var orderLine = db.OrderLines.
    Where(ol => ol.ID == orderLineID select ol).
    First();
// navigate to order via the association
var order = orderLine.GetOrder();

我得到的基本上是 GetOrder() 的空结果。

但如果我这样做：

var orderLine = (from ol in db.OrderLines where ol.ID == orderLineID).First();
var order = orderLine.GetOrder();

效果很好。

什么会导致这种情况？这是一个错误吗？

编辑：这是与 Lambda 表达式一起使用的实际代码，注释掉了它不起作用

var msg = db.Messages.Where(m => m.ID == msgID).First();
if (msg.SentTS.HasValue) return;

// Get the message recipients
// I don't get it.. why doesn't lambda expressions work here? returns 0 results!
// var testtos = msg.GetMessageTos.Where(mt => mt.Active);
var tos = from mt in db.MessagesTos
          where mt.Active && mt.MessageID == msgID
          select mt;

原文

Has anyone had problems gettting associations to load using LINQ to SQL when your child record was loaded via a lambda query? For example:

var orderLine = db.OrderLines.
    Where(ol => ol.ID == orderLineID select ol).
    First();
// navigate to order via the association
var order = orderLine.GetOrder();

What I get basically is a null result from GetOrder().

But if I do this instead:

var orderLine = (from ol in db.OrderLines where ol.ID == orderLineID).First();
var order = orderLine.GetOrder();

Works fine.

What can cause this? Is this a bug?

EDIT: Here's the actual code that WORKS with the Lambda expression commented out that DOESN'T WORK

var msg = db.Messages.Where(m => m.ID == msgID).First();
if (msg.SentTS.HasValue) return;

// Get the message recipients
// I don't get it.. why doesn't lambda expressions work here? returns 0 results!
// var testtos = msg.GetMessageTos.Where(mt => mt.Active);
var tos = from mt in db.MessagesTos
          where mt.Active && mt.MessageID == msgID
          select mt;

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国际总奸 2024-09-22 10:50:51

你也可以试试这个，我觉得这样更干净一点。

var orderLine = db.OrderLines.Single( ol => ol.ID == orderLineID ); 
var order = orderLine.GetOrder();

我相信在您的非工作示例中您想使用 .First() 而不是 .Single() 。

You can also try this, I think it's a little cleaner.

var orderLine = db.OrderLines.Single( ol => ol.ID == orderLineID ); 
var order = orderLine.GetOrder();

I beileive in your non-working example you want to use .First() instead of .Single().

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阿楠 2024-09-22 10:50:51

在我看来，问题更多地与关联有关，而不是与 lambda 表达式有关。

在您的场景中，这应该有效：

var tos = db.MessagesTos.Where(mt=> mt.Active && mt.MessageID);

虽然这不会：

var tos = from mt in msg.SentTS
          where mt.Active
          select mt;

至于为什么它不起作用，我建议查看设计器中的关联并检查其是否正确匹配数据库模型（匹配正确的列）。我还建议确认 msg.SentTS 实际上是空的，无论您对其运行任何进一步的查询。

It seems to me that the problem has more to do with the association than lambda expressions.

In your scenario, this should work:

var tos = db.MessagesTos.Where(mt=> mt.Active && mt.MessageID);

while this won't:

var tos = from mt in msg.SentTS
          where mt.Active
          select mt;

As to why it doesn't work, I suggest taking a look at the association in the designer and checking its matching the db model correctly (matching the correct columns). I also suggest to confirm that msg.SentTS is effectively coming empty, regardless of any further query you run on it.

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