Linq sql - where should I put phrase with "where" - linq

Question

This is my query, an it almost works. I need to add to this query " where(k.IdUser == d.UserDoc.
The problem appears when I add this. Wherever I put this it stops working. Join isn't option here.
var documents = (from d in DocumentDAO.GetDocument()
from k in UserDAO.GetUsers()
where (DateTime.Now <= d.ExpirationDate)
select new DocumentUI
{
Title = d.Title,
Description = d.Description,
DateOfAdd = d.DateOfAdd,
ExpirationDate = d.ExpirationDate,
UserDoc = d.UserDoc,
User = new UserUI {
FirstName = k.FirstName,
LastName = k.LastName}
}).ToList();
My app gets the data from database and show this data in window. If I start my app with this query ( I have only one documents in db) it shows me the same document but with all Users, and I want to my application shows me only this user who Id is as foreign key in documents (UserDoc).
I tried somethig like this:
var documents = (from d in DocumentDAO.GetDocument()
from k in UserDAO.GetUsers()
where ((DateTime.Now <= d.ExpirationDate) && (d.UserDoc == k.IdUser))
select new DocumentUI
{
Title = d.Title,
Description = d.Description,
DateOfAdd = d.DateOfAdd,
ExpirationDate = d.ExpirationDate,
UserDoc = d.UserDoc,
User = new UserUI {
FirstName = k.FirstName,
LastName = k.LastName}
}).ToList();
And:
var documents = (from d in DocumentDAO.GetDocument()
from k in UserDAO.GetUsers().Where(k => k.IdUser == d.UserDoc)
where (DateTime.Now <= d.ExpirationDate)
select new DocumentUI
{
Title = d.Title,
Description = d.Description,
DateOfAdd = d.DateOfAdd,
ExpirationDate = d.ExpirationDate,
UserDoc = d.UserDoc,
User = new UserUI {
FirstName = k.FirstName,
LastName = k.LastName}
}).ToList();
and in both case my app shows me nothing
this it class DocumentUI:
public class DocumentUI
{
public string Title { get; set; }
public string Description { get; set; }
public DateTime DateOfAdd { get; set; }
public DateTime ExpirationDate { get; set; }
public int UserDoc { get; set; }
public UserUI User { get; set; }
}

Answer 1

The below query (Same as your first Query) should return List<DocumentUI> provided you have proper data which satisfy ((DateTime.Now <= d.ExpirationDate) && (d.UserDoc == k.IdUser))
var documents = (from d in DocumentDAO.GetDocument()
join k in UserDAO.GetUsers()
on d.UserDoc equals k.IdUser
where (d.ExpirationDate >= DateTime.Now)
select new DocumentUI
{
Title = d.Title,
Description = d.Description,
DateOfAdd = d.DateOfAdd,
ExpirationDate = d.ExpirationDate,
UserDoc = d.UserDoc,
User = new UserUI {
FirstName = k.FirstName,
LastName = k.LastName}
}).ToList();
Still, If you are not getting result verify the values in Var documents = DocumentDAO.GetDocument(), var users = UserDAO.GetUsers().