Can you mix string and object outputs in SQL JSON? - json

Question

I'm trying to construct a JSON-serialized list of key/value pair items from my SQL database (compat level 140). The trick is that the values can be anything: numbers, strings, null, or other JSON objects.
It should be able to look something like this:
[{"key":"key1","value":"A String"},{"key":"key2","value":{"InnerKey":"InnerValue"}}]
However, SQL seems to be forcing me to select either a string or an object.
SELECT
[key] = kvp.[key],
[value] = CASE
WHEN ISJSON(kvp.[value]) = 1 THEN JSON_QUERY(kvp.[value])
ELSE '"' + kvp.[value] + '"' -- See note below
END
FROM (VALUES
('key1', 'This value is a string')
,('key2', '{"description":"This value is an object"}')
,('key3', '["This","value","is","an","array","of","strings"]')
,('key4', NULL)
-- Without these lines, the above 4 work fine; with either of them, even those 4 are broken
--,('key5', (SELECT [description] = 'This value is a dynamic object' FOR JSON PATH, WITHOUT_ARRAY_WRAPPER))
--,('key6', JSON_QUERY((SELECT [description] = 'This value is a dynamic object' FOR JSON PATH, WITHOUT_ARRAY_WRAPPER)))
) AS kvp([key], [value])
FOR JSON PATH
Am I trying to do something that SQL can't support, or am I just missing the proper syntax for making this work?
*Note that the addition of the double-quotes seems like it shouldn't be necessary. But without those, SQL fails to wrap the string and generates bad JSON:
[{"key":"key1","value":This value is a string},...

Answer 1

If your query is modified to this, it works:
SELECT
[key] = kvp.[key],
[value] = ISNULL(
JSON_QUERY(CASE WHEN ISJSON(kvp.[value]) = 1 THEN kvp.[value] END),
'"' + STRING_ESCAPE(kvp.[value], 'json') + '"'
)
FROM (VALUES
('key1', 'This value is a "string"')
,('key2', '{"description":"This value is an object"}')
,('key3', '["This","value","is","an","array","of","strings"]')
,('key4', NULL)
-- These now work
,('key5', (SELECT [description] = 'This value is a dynamic object' FOR JSON PATH, WITHOUT_ARRAY_WRAPPER))
,('key6', JSON_QUERY((SELECT [description] = 'This value is a dynamic object' FOR JSON PATH, WITHOUT_ARRAY_WRAPPER)))
) AS kvp([key], [value])
FOR JSON PATH, INCLUDE_NULL_VALUES
Of course, this wouldn't be sufficient if value was an int. Also, I can't really explain why yours doesn't work.