Question

I am working on an ASP.NET application using LinqToSQL. When the page loads I run a query and save the results into a variable… var tasks = query expression. I then save this into a session variable Session["Tasks"] = tasks…

Is it possible to cast this session object back to its original var state, so I can run methods such as Count(), Reverse() and so on?

Thanks

Answer 1

var is just short-hand for type inference… the real question here is: what is the underlying type?

If it involves an anonymous type (i.e. new {…}, or a List<> there-of), then there is no elegant way (although it can be done in a hacky way). In short; don’t use anonymous types in this scenario…

Note that a query expression such as IQueryable<T> is not data – it is a query – to store the data (for a cache) you’d need to use .ToList() / .ToArray() etc.

Important: you shouldn’t store a query expression in session; at best (in-memory session provider) that will keep the data-context alive; at worst (database etc session provider) it won’t work, as a data-context isn’t serializable. Storing results from a query is fine; but otherwise, rebuild the query expression per-request.

In which case, you might be able to use (for example):

var tasksQuery = from task in ctx.Tasks
             where task.IsActive
             orderby task.Created
             select task; // this is IQueryable<Task>

Session["Tasts"] = tasksQuery.ToArray(); // this is Task[]
...
var tasks = (Task[]) Session["Tasts"]; // this is Task[]