Question

我有以下代码：

ServiceSoapClient service = new ServiceSoapClient();
    var dataSource = (from u in _db.Sessions
                      where u.DeletedOn == null
                      select new
                      {
                          SessionId = u.UploadSessionId,
                          FileName = u.FileName,
                          CreatedBy = u.User.UserName,
                          Partner = u.Company.Name,
                          CreatedOn = u.CreatedOn,
                          Visible = service.IsSessionProcessing(u.UploadSessionId)
                      })
                    .OrderByDescending(x => x.CreatedOn);

...当然这里的问题是Visible = service.IsSessionProcessing(u.UploadSessionId)部分有权访问修改后的闭包，因为当我在某处使用dataSource，即预成型.ToList()或类似的东西时实际计算表达式

这里的问题是我无法立即执行.ToList()，因为我需要将其用作控件的数据源。

Linq有什么方法可以避免这种情况吗？我可以在表达式中使用局部变量，以便使用实际值计算它吗？

Answer 1

这里的“修改后的闭包”是service。所以...不要重新分配service。

Answer 2

真正的错误在于尝试在表达式的上下文中调用函数，这对于表示数据库操作的表达式没有任何意义。我想你实际上尝试了以下内容：

// Database operation, no soap client funny business here.
 var list = (
  from u in _db.Sessions
  where u.DeletedOn == null
  orderby x.CreatedOn descending
  select new
  {
   SessionId = u.UploadSessionId,
   FileName = u.FileName,
   CreatedBy = u.User.UserName,
   Partner = u.Company.Name,
   CreatedOn = u.CreatedOn,
  }).ToList();

// From now on you are not in a database anymore, it's pure linq-to-objects. You can call the service.
ServiceSoapClient service = new ServiceSoapClient();
var dataSource = (from u in list select new {
 SessionId = u.SessionId,
 FileName = u.FileName,
 CreatedBy = u.CreatedBy,
 Partner = u.Partner,
 CreatedOn = u.CreatedOn,
 Visible = service.IsSessionProcessing(u.SessionId)
}).ToList();

如何避免在linq表达式中访问修改后的闭包？

2 个答案: