Get hierarchical data is SQL SERVER with fallback logic - sql

Question

Consider the below schema
dbo.Cultures (Id, CultureCode, ParentId)
Culture table stores the data in the parent-child relationship.
Suppose we have below demo data
5 es-ES 3
Now I have another table which stores the multilingual data for the different cultures.
Schema for the table is as following
dbo.LangData(KeyName, CultureId, Value)
here cultureId is the foreign key of dbo.Cultures table.
Suppose this table has following data
Now I require to fetch the data for all the cultures which are in the Culture table and the corresponding value column in the LangData table.
The culture Ids which are not in the LangData table, for those the Value column will the value of the corresponding parent culture Id columns value. I.e. Data will be retrieved using fallback logic
E.g. For the above values the Result set will be following.
5 es-ES Colour_IN
Here for de-DE data is missing in LangData so it's value will be the data in it's parent culture i.e. en-IN, if in case data also not found in en-IN then it will pick the data of it's parent en-US.
Tried Soloution
First I fetch the culture hierarchy using CTE
CREATE FUNCTION [dbo].[ufnGetCultureHierarchyAll] ()
RETURNS #hierarchyResult TABLE(RowNo INT, CultureId INT, ParentCultureId INT)
AS
BEGIN
WITH CultureHierarchy_CTE(RowNo, CultureId, ParentCultureId)
AS (
SELECT 1,
Id,
ParentId
FROM [dbo].Cultures
UNION ALL
SELECT RowNo + 1,
ou.Id,
ou.ParentId
FROM [dbo].Cultures ou
JOIN CultureHierarchy_CTE cte
ON ou.Id = cte.ParentCultureId
)
-- inserting desired records into table and returning
INSERT INTO #hierarchyResult (RowNo,CultureId,ParentCultureId )
SELECT RowNo, CultureId , ParentCultureId FROM CultureHierarchy_CTE
RETURN;
END
This will return the hierarchy of the all the cultures
Now I attempted to apply join of the result set with the LangData table,
DECLARE #cultureHierarchy AS TABLE(
RowNumber INT,
CultureId INT,
ParentCultureId INT
)
--SELECT * FROM master.Cultures
----Get and store culture hierarchy
INSERT INTO #cultureHierarchy
SELECT RowNo, CultureId, ParentCultureId
FROM ufnGetCultureHierarchyAll()
SELECT c.Code AS [CultureCode],
c.CultureId AS [CultureId],
rv.Value
FROM dbo.LangData rv WITH (NOLOCK)
JOIN #cultureHierarchy c ON rv.CultureId = c.CultureId
END
but it is not working.
Is someone have any Idea regarding same.

Answer 1

Solution using Itzik Ben-Gan's hierarchy model. If you can extend the dbo.Cultures table with Hierarchy, Lvl and Root columns and index on Hierarchy, query will be faster. It has to be rewrited in that case though.
drop table if exists dbo.Cultures;
create table dbo.Cultures (
ID int
, Code varchar(50)
, ParentID int
);
insert into dbo.Cultures (ID, Code, ParentID)
values (1, 'en-US', null), (2, 'en-IN', 1), (3, 'de-DE', 2), (4, 'hi-HI', 2)
drop table if exists dbo.LangData;
create table dbo.LangData (
KeyName varchar(100)
, CultureID int
, Value varchar(100)
);
insert into dbo.LangData (KeyName, CultureID, Value)
values ('lblColourName', 1, 'Color'), ('lblColourName', 2, 'Colour-IN');
with cteCultures as (
select
c.ID, c.Code, c.ParentID, 0 as Lvl
, convert(varchar(max), '.' + CONVERT(varchar(50), c.ID) + '.') as Hierarchy
, c.ID as Root
from dbo.Cultures c
where c.ParentID is null
union all
select
c.ID, c.Code, c.ParentID, cc.Lvl + 1 as Lvl
, cc.Hierarchy + convert(varchar(50), c.ID) + '.' as Hierarchy
, cc.Root as Root
from dbo.Cultures c
inner join cteCultures cc on c.ParentID = cc.ID
)
select
ccr.ID
, ccr.Code
, coalesce(ld.Value, ld2.Value) as Value
from cteCultures ccr
left join dbo.LangData ld on ccr.ID = ld.CultureID
outer apply (
select
top (1) tcc.ID
from cteCultures tcc
inner join dbo.LangData tld on tcc.ID = tld.CultureID
where ld.KeyName is null
and ccr.Hierarchy like tcc.Hierarchy + '%'
and ccr.Hierarchy <> tcc.Hierarchy
order by tcc.Lvl desc
) tt
left join dbo.LangData ld2 on tt.ID = ld2.CultureID

Answer 2

If I understand your question:
We just build your hierarchy (SEQ and Lvl are optional) and then perform TWO left joins in concert with a Coalesce().
Example
Declare #Cultures table (id int,ParentId int,Code varchar(50))
Insert into #Cultures values
( 1, NULL,'en-US')
,( 2, 1 ,'en-IN')
,( 3, 2 ,'de-DE')
,( 4, 2 ,'hi-HI')
Declare #LangData table (keyName varchar(50),CultureId int,Value varchar(50))
Insert Into #LangData values
('lblColourName',1,'Color')
,('lblColourName',2,'Color_IN')
;with cteP as (
Select Seq = cast(10000+Row_Number() over (Order by Code) as varchar(500))
,ID
,ParentId
,Lvl=1
,Code
From #Cultures
Where ParentId is null
Union All
Select Seq = cast(concat(p.Seq,'.',10000+Row_Number() over (Order by r.Code)) as varchar(500))
,r.ID
,r.ParentId
,p.Lvl+1
,r.Code
From #Cultures r
Join cteP p on r.ParentId = p.ID)
Select CultureId = A.ID
,A.Code
,Value = Coalesce(C.Value,B.Value)
From cteP A
Left Join #LangData B on (A.ParentId=B.CultureId)
Left Join #LangData C on (A.Id=C.CultureId)
Order By Seq
Returns
CultureId Code Value
1 en-US Color
2 en-IN Color_IN
3 de-DE Color_IN
4 hi-HI Color_IN