Two virtually calculated columns in view

Initially in a regular table, there are two columns Key and ParentKey. The Key gets its value as an identity column - automatically. ParentKey - by the expression

 WITH
  latest
  as
(
  SELECT
   ProductID,
   Date,
   [Key],
    ROW_NUMBER() OVER (
      PARTITION BY  ProductID
          ORDER BY [Date] DESC -- order by latest Date
    ) rn 
  FROM
   [MyTable]
)


UPDATE      
  u 
SET
  u.[ParentKey] = latest.[Key] 
FROM
   [MyTable] u
INNER JOIN
  latest
    ON u.ProductID = latest.ProductID
WHERE
  latest.rn = 1

Does it possible to combine both of these two steps simultaneously when creating the View (Key and ParentKey becomes virtual)? I have a solution for the first part of these task - creating Key column in a view. Could it be combined with the step which then sets ParentKey?

Current Code

CREATE VIEW v_Test 

AS
SELECT
ProductID
,Date,
CAST (ROW_NUMBER() OVER( ORDER BY [ProductID] ) AS int) as [Key]

-- some expression for ParentKey?

FROM [MyTable]

Desired View output (Key and ParentKey must be processed during view creation)

+-------------------------------------------------
|ProductID  |   Date        |  Key   |  ParentKey 
+-------------------------------------------------
|111        |   2017-12-31  |   1    |   3
|111        |   2018-12-31  |   2    |   3
|111        |   2019-12-31  |   3    |   3
|222        |   2017-12-31  |   4    |   6
|222        |   2018-12-31  |   5    |   6
|222        |   2019-12-31  |   6    |   6
|333        |   2017-12-31  |   7    |   9
|333        |   2018-12-31  |   8    |   9
|333        |   2019-12-31  |   9    |   9

If I have understood what you are trying to do correctly then you can put the query with the row number in a CTE or derived table and then reference that in a windowed aggregate to get the max.

CREATE VIEW v_Test
AS
  WITH T
       AS (SELECT ProductID,
                  Date,
                  ROW_NUMBER() OVER(ORDER BY [ProductID] ASC,  [Date] ASC ) AS [Key]
           FROM   [MyTable])
  SELECT ProductID,
         Date,
         [Key],
         MAX([Key]) OVER (PARTITION BY [ProductID]) AS [ParentKey]
  FROM   T 

These "Keys" will not be at all stable over time though as they can change after inserts for unrelated products.

If I understand you correctly, I believe will be much shorter using only MAX with OVER clause. Something like

UPDATE      
  u 
SET
  u.[ParentKey] = 
FROM
   [MyTable] u
CROSS APPLY (SELECT MAX( [Key] OVER ( PARTITION BY ProductID ORDER BY [DATE] DESC ) LatestKey ) ca