How to generate hierarchical JSON data with Microsoft SQL Server 2016?

Question

I\'m using Microsoft SQL Server 2016. This version supports JSON.

I have a Person table with the following data:

Pe         


        

Answer 1

Sure It would be very hard (if not impossible) to implement a Json tree using recursive CTE.

However, using recursive function is really helpful and solves the Problem:

ALTER  FUNCTION fn_Json(@PersonId INT, @IsRoot INT ) 
RETURNS VARCHAR(MAX)
BEGIN 
    DECLARE @Json NVARCHAR(MAX) = '{}', @Name NVARCHAR(MAX) , @Children                 NVARCHAR(MAX)

    SET @Json =  
    (SELECT P.Name ,JSON_QUERY(dbo.fn_Json(P.PersonId, 2) ) AS Children 
    FROM dbo.Persons AS P  
    WHERE P.FatherId = @PersonId 
    FOR JSON AUTO);

    IF(@IsRoot = 1) 
    BEGIN
       SELECT @Name = P.Name FROM dbo.Persons AS P WHERE P.PersonId = @PersonId
       SET @Json =   '{"Name":"' + @Name + '","Children":' + CAST(@Json AS NVARCHAR(MAX)) + '}'
       SET @IsRoot = 2
    END

    RETURN @Json 
END 

GO

It worth mentioning that functions can not be built if its interior objects are invalid. Therefore, it is necessary to build the function as:

CREATE FUNCTION fn_Json(@PersonId INT, @IsRoot INT) 
RETURNS VARCHAR(MAX)
BEGIN 
   RETURN 1
END 

and then to use the fist code. If you want that the root node is included set

@IsRoot = 1

if not @IsRoot = 2 or some other values