Get Hieararchical data as JSON from SQL Server - sql

Question

I have following table:
Id
HieararchyId
Name
1
/
MHz
2
/1/
Finance
3
/1/
IT
4
/1/3/
Software Development
5
/1/3/
QA
6
/1/2/
Accountant
and I want to get data for my TreeView like:
[
{
"Id": 1,
"HierarchyId": "/"
"Name":"MHz",
"Children":[
{
"Id": 3,
"HierarchyId": "/1/"
"Name":"IT",
"Children":[
{
"Id": 4,
"HierarchyId": "/1/3/"
"Name":"Software Development",
"Children":[]
}
{
"Id": 5,
"HierarchyId": "/1/3/"
"Name":"QA",
"Children":[]
}
]
},
{
"Id": 2,
"HierarchyId": "/1/"
"Name":"Finance",
"Children":[
{
"Id": 6,
"HierarchyId": "/1/2/"
"Name":"Accountant",
"Children":[]
}
]
}
]
}
]
I tried with this: How to generate hierarchical JSON data
Got error: No more lock classes available from transaction.
Or is it better creating recursive function and filling the Tree on client side?
Update
CREATE FUNCTION dbo.GetJson (#departmentId hierarchyid)
RETURNS nvarchar(max)
AS BEGIN
RETURN (
SELECT
Id,
HierarchyId,
Name,
children = JSON_QUERY(dbo.GetJson(HierarchyId))
FROM Departments p
WHERE p.HierarchyId.IsDescendantOf(#departmentId ) = 1
FOR JSON PATH
);
END;

Answer 1

The best way I have found to do this is to use a recursive function.
You can self-join all nodes and check if they are a child using GetAncestor
CREATE FUNCTION dbo.GetJson (#parentID hierarchyid)
RETURNS nvarchar(max)
AS BEGIN
RETURN (
SELECT
t.Id,
t.HierarchyId,
t.Name,
children = JSON_QUERY(dbo.GetJson(t.HierarchyId))
FROM Tree t
WHERE t.HierarchyId <> #parentID
AND t.HierarchyId.GetAncestor(1) = #parentID
FOR JSON PATH
);
END;
go
SELECT dbo.GetJson(hierarchyid::GetRoot());
db<>fiddle
Result
[
{
"Id": 1,
"HierarchyId": "/1/",
"Name": "MHz",
"children": [
{
"Id": 2,
"HierarchyId": "/1/2/",
"Name": "Finance",
"children": [
{
"Id": 6,
"HierarchyId": "/1/2/6/",
"Name": "Accountant"
}
]
},
{
"Id": 3,
"HierarchyId": "/1/3/",
"Name": "IT",
"children": [
{
"Id": 4,
"HierarchyId": "/1/3/4/",
"Name": "Software Development"
},
{
"Id": 5,
"HierarchyId": "/1/3/5/",
"Name": "QA"
}
]
}
]
}
]