LINQ，“参数类型不匹配”错误，这是什么意思，我该如何解决？

发布于 2024-09-04 12:58:51 字数 561 浏览 4 评论 0原文

我是 linq 的新手，我正在尝试将数据绑定到匿名类型。

我使用 SubSonic 3.0 作为我的 DAL。

我正在从 2 个表中进行选择，如下所示

        var myDeal = (from u in db.Users
                  select new
                      {
                          UserID = u.UserID,
                          UserRoleID = (from ur in u.UserRoles where u.UserRoleID == ur.UserRoleID select ur).FirstOrDefault().UserRoleID
                      });
    foreach (var v in myDeal) //dies first time here
    {
    }

然后当我进行数据绑定或尝试迭代集合时，我在运行时收到“参数类型不匹配”错误。

我不确定这里发生了什么事。

原文

I'm new to linq and I'm trying to databind to an anonymous type.

I'm using SubSonic 3.0 as my DAL.

I'm doing a select from 2 tables like so

        var myDeal = (from u in db.Users
                  select new
                      {
                          UserID = u.UserID,
                          UserRoleID = (from ur in u.UserRoles where u.UserRoleID == ur.UserRoleID select ur).FirstOrDefault().UserRoleID
                      });
    foreach (var v in myDeal) //dies first time here
    {
    }

Then when I databind or try to iterate through the collection I get the "Argument types do not match" error during run time.

I'm not sure what is going on here.

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桃扇骨 2024-09-11 12:58:51

ID 字段之一可以为空吗？

如果是这样，您需要访问 .Value 属性

var myDeal = (from u in db.Users 
        join ur in     
              select new 
                   { 
                     UserID = u.UserID, 
                     UserRoleID = (from ur in u.UserRoles where u.UserRoleID.Value equals ur.UserRoleID select ur).FirstOrDefault().UserRoleID 
                    });

您也可以尝试如下操作：

var myDeal = (from u in db.Users
         join ur in db.UserRoles
        on new {ID = u.UserRoleID.value} equals new {ID = ur.UserRoleID} into tempRoles
        from roles in tempRoles.DefaultIfEmpty()
        select new
        {
           UserID = u.UserID, 
                 UserRoleID = roles.UserRoleID
        });

您使用 tempRoles 执行左外连接。因此，如果没有分配角色，您仍然可以获得用户 ID。

我还没有测试过这个，这只是我的想法。

祝你好运，

帕特里克。

Is one of the ID fields nullable?

If so, you need to access the .Value property

var myDeal = (from u in db.Users 
        join ur in     
              select new 
                   { 
                     UserID = u.UserID, 
                     UserRoleID = (from ur in u.UserRoles where u.UserRoleID.Value equals ur.UserRoleID select ur).FirstOrDefault().UserRoleID 
                    });

You could also try something like this:

var myDeal = (from u in db.Users
         join ur in db.UserRoles
        on new {ID = u.UserRoleID.value} equals new {ID = ur.UserRoleID} into tempRoles
        from roles in tempRoles.DefaultIfEmpty()
        select new
        {
           UserID = u.UserID, 
                 UserRoleID = roles.UserRoleID
        });

You use tempRoles to execute a left outer join. So if there is no role assigned, you still get the userID.

I haven't tested this, this is just off the top of my head.

Good Luck,

Patrick.

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