Creating JSON Nested Level Arrays with Query - json

Question

I'm trying to recreate a JSON output that is about 5 levels deep. I can recreate 2 levels deep, but after that, I'm stumped. It has worked using FOR JSON AUTO, but I need control over the naming and how they appear, so I need to be able to use FOR JSON PATH.
Below is sample code and would allow for a 3 level deep output. I'm hoping that whatever is needed to make it 3 levels, I can learn from to go to 5 levels.
CREATE TABLE [FamilyTree](
[ID] INT NOT NULL ,
[Name] VARCHAR(250) NOT NULL,
[ParentID] INT NOT NULL,
) ON [PRIMARY]
GO
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(1,N'Person1',0)
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(2,N'Person2',0)
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(3,N'Person3',1)
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(4,N'Person4',2)
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(5,N'Person5',3)
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(6,N'Person6',3)
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(7,N'Person7',4)
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(8,N'Person8',4)
INSERT [FamilyTree]([ID],[Name],[ParentID])
VALUES(9,N'Person9',4)
Using this query:
SELECT
FT1.Name AS [name],
(SELECT Name FROM FamilyTree WHERE ParentID = FT1.ID FOR JSON PATH) children
FROM FamilyTree FT1
WHERE FT1.ParentID = 0
FOR JSON PATH
I can get the following output:
[
{
"name": "Person1",
"children": [
{
"Name": "Person3"
}
]
},
{
"name": "Person2",
"children": [
{
"Name": "Person4"
}
]
}
]
but I want to be able to get it to go even further to look like this:
[
{
"name": "Person1",
"children": [
{
"Name": "Person3",
"children": [
{
"name": "Person 5",
"name": "Person 6",
}
]
}
]
},
{
"name": "Person2",
"children": [
{
"name": "Person4",
"children": [
{
"name": "Person 7",
"name": "Person 8",
"name": "Person 9"
}
]
}
]
}
]

Answer 1

You can just keep nesting subqueries if you want
SELECT
ft1.ID,
ft1.Name,
ft2.children
FROM FamilyTree ft1
CROSS APPLY (
SELECT
ft2.ID,
ft2.Name,
ft3.children
FROM FamilyTree ft2
CROSS APPLY (
SELECT
ft3.ID,
ft3.Name,
ft4.children
FROM FamilyTree ft3
CROSS APPLY (
SELECT
ft4.ID,
ft4.Name,
ft5.children
FROM FamilyTree ft4
CROSS APPLY (
SELECT
ft5.ID,
ft5.Name
FROM FamilyTree ft5
WHERE ft5.ParentID = ft4.ID
FOR JSON PATH
) ft5(children)
WHERE ft4.ParentID = ft3.ID
FOR JSON PATH
) ft4(children)
WHERE ft3.ParentID = ft2.ID
FOR JSON PATH
) ft3(children)
WHERE ft2.ParentID = ft1.ID
FOR JSON PATH
) ft2(children)
WHERE ft1.ParentID IS NULL
FOR JSON PATH;
db<>fiddle
To do this recursively, or for that matter to prevent duplication of code, you cannot use a Table Valued Function. You can only do this with a scalar UDF (oh the horror!).
CREATE OR ALTER FUNCTION dbo.GetJson (#ParentID int)
RETURNS nvarchar(max)
AS
BEGIN
RETURN (
SELECT
ft.ID,
ft.Name,
children = dbo.GetJson(ft.ID)
FROM FamilyTree ft
WHERE EXISTS (SELECT ft.ParentID INTERSECT SELECT #ParentID) -- null compare
FOR JSON PATH
);
END;
SELECT dbo.GetJson(NULL);
db<>fiddle
Note that in both of these examples, root nodes have a ParentID of NULL not 0. This is the correct way to do it, as there is no 0 row.

Answer 2

Try this, Mabe its usful:
DECLARE #FamilyTree TABLE (
[ID] INT NOT NULL ,
[Name] VARCHAR(250) NOT NULL,
[ParentID] INT NOT NULL
)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(1,N'Person1',0)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(2,N'Person2',0)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(3,N'Person3',1)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(4,N'Person4',2)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(5,N'Person5',3)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(6,N'Person6',3)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(7,N'Person7',4)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(8,N'Person8',4)
INSERT #FamilyTree([ID],[Name],[ParentID])
VALUES(9,N'Person9',4)
SELECT
FT1.Name AS [name],children.Name,grandchild.Name AS grandchild
FROM #FamilyTree FT1
INNER JOIN (SELECT * FROM #FamilyTree ) children ON children.ParentID = FT1.ID
INNER JOIN (SELECT * FROM #FamilyTree ) grandchild ON grandchild.ParentID = children.ID
WHERE FT1.ParentID = 0
FOR JSON AUTO
For each level, you can set another "INNER JOIN"
It's the result:
[
{
"name": "Person1",
"children": [
{
"Name": "Person3",
"grandchild": [
{
"grandchild": "Person5"
},
{
"grandchild": "Person6"
}
]
}
]
},
{
"name": "Person2",
"children": [
{
"Name": "Person4",
"grandchild": [
{
"grandchild": "Person7"
},
{
"grandchild": "Person8"
},
{
"grandchild": "Person9"
}
]
}
]
}
]