Using a recursive CTE in a view - sql

Question

Having a typical parent/child hierarchy table it's a common thing to query it using Common Table Expression:
with CTE as (
select Id, ProviderId, ConsumerId
from T1
where ProviderId in (2, 3, 9)
union all
select T1.Id, T1.ProviderId, T1.ConsumerId
from T1
join CTE on C.ProviderId = CTE.ConsumerId
)
select * from CTE
Is it possible to create a view based on this query so that one can do:
select * from MagicView where ProviderId in (2,3,9)
In other words, can we somehow extract parameters from the anchor part of the CTE to create a generic view?

Answer 1

Create a TVF:
CREATE FUNCTION my_function (
#ProviderId int
)
RETURNS #ProviderTable TABLE
(
Id int NULL,
ProviderId int NULL,
ConsumerId int NULL
)
AS
BEGIN
WITH cte AS (
SELECT Id,
ProviderId,
ConsumerId
FROM T1
WHERE ProviderId in (#ProviderId)
UNION ALL
SELECT t.Id,
t.ProviderId,
t.ConsumerId
FROM T1 t
INNER JOIN cte c
ON t.ProviderId = c.ConsumerId
)
INSERT INTO #ProviderTable
SELECT * FROM cte;
RETURN;
END;
Than create a view:
CREATE VIEW my_view
AS
SELECT m.*
FROM Providers p
CROSS APPLY my_function (p.ProviderId) m
After that you can SELECT from view whatever you need:
SELECT *
FROM my_view
WHERE ProviderId in (2,3,9)
OPTION (MAXRECURSION 0)

Answer 2

One way to do Table Valued Route
CREATE FUNCTION [dbo].[MVParam_tvf](#ParameterString nvarchar(4000), #Delimiter char(1)= ',')
RETURNS #VALUES TABLE (Param nvarchar(4000))AS
Figure out your code preference to spilt delimited string to table
END
CREATE FUNCTION dbo.MagicView_tvf
(
#ParameterString NVARCHAR(4000)
,#Delimiter CHAR(1)
)
RETURNS TABLE
AS
RETURN
(
with CTE as (
select Id, ProviderId, ConsumerId
from
T1 t
INNER JOIN MVParam_tvf (#ParameterString, #Delimiter) p
ON CAST(t.ProviderId AS VARCHAR(10)) = p.OutPutColumn
union all
select T1.Id, T1.ProviderId, T1.ConsumerId
from T1
join CTE on C.ProviderId = CTE.ConsumerId
)
select * from CTE
)
GO
SELECT * FROM dbo.MagicView_tvf ('2,3,9')
If you want to go the view route create the view without the where line on anchor part of cte and then when you call it write your where statement on that query.