Question

I thought its possible to save multiple linq queries from a loop in a single variable ?

public ActionResult Index()
    {
        string ActiveUserId = (string)Session["ActiveUserGuid"];
        Guid MyGuid = new Guid(ActiveUserId);

        var queryRoots = from r in db.Roots
                         where r.UserId == MyGuid
                         select r.TaskId;

//Here is the questionable Part
        foreach (var i in queryRoots)
        {             
            var queryAllTasks = from t in db.Tasks
                                join b in db.Trees on t.TaskId equals b.ChildId
                                where b.TaskId == i
                                select t;
            tasksForView.Add(queryAllTasks); <---????? obviously doesnt work
        };

        return View(queryAllTasks);
    }

public class Root
{
    public int RootId { get; set; }

    public Guid UserId { get; set; }
    public User User { get; set; }  //navigation Property

    public int TaskId { get; set; } // composite key
    public int ChildId { get; set; }
    public Tree Tree { get; set; } //navigation Property
}

public class Tree
{
    public int TaskId { get; set; }
    public int ChildId { get; set; }
    public int Length { get; set; } //Path length

    public virtual ICollection<Root> Roots { get; set; }

}

In case you are wondering what its supposed to do. I want to query several subtrees from a hierarchical transitiv closure table and return them to a view.

I know my code is not close to working and I just tried very simple solutions!
I guess a different way to do the query would get rid of the problem all together

Answer 1

Use Contains on your integer list:

var tasks = 
    from t in db.Tasks
    join b in db.Trees on t.TaskId equals b.ChildId
    where queryRoots.Contains(b.TaskId)
    select t;

return View(tasks);

or do it all in one query:

var tasks = 
    from t in db.Tasks
    join b in db.Trees on t.TaskId equals b.ChildId
    join r in db.Roots on r.TaskId equals b.TaskId
    where r.UserId == MyGuid
    select t;

return View(tasks);