CODEWITHSUNDEEP
c#linqclosures
TehBoyan
TehBoyan

Reputation: 6890

How to avoid access to modified closure in linq expression?

I have the following code:

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);

...of course the problem here is the Visible = service.IsSessionProcessing(u.UploadSessionId) portion that has access to modified closure because the expression is actually calculated when I use dataSource somewhere i.e preform .ToList() or something similar.

The problem here is that I can't perform .ToList() immediately because I need to use it as a data source for a control as it is.

Is there any way to avoid this in Linq? Can I use a local variable in the expression itself so that it gets calculated with the real values?

Upvotes: 1

Views: 719

Answers (2)

George Polevoy
George Polevoy

Reputation: 7671

The real bug is in trying to call function in context of expression, which make no sence for an expression representing a database operation. I suppose you actually tried the following:

// 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();

Upvotes: 0

Marc Gravell
Marc Gravell

Reputation: 1062512

The "modified closure" here is service. So... don't reassign service.

Upvotes: 1

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