In SQL Server, how to update/merge a json with another json, without explicitly using the keys / defining columns?
Some background: I store metadata as a json in a varchar(max) column. Each record can have different metadata keys in the same table. Like storing People and Products in the same table. Similar to EAV data model but instead of value table I use json column to store the metadata as key-value pairs.
That is why I am looking for a generic solution.
i.e. one record can have metadata
{"last_name":"John","first_name":"Smith","age":28,"Address":"123 Steels st…"}
another record in the same table can have metadata
{"product_name":"Box","material":"plastic","Price":1.5,"Weight":20,"Height":15}
I am looking for an efficient/modern way to update/add multiple values in a json, from a json.
i.e. source
{
"last_name": "John",
"first_name": "Smith",
"age": 28,
"weight":79
"address": "123 Steels st…"
}
what to update/add:
{
"address": "567 Yonge Ave…"
"last_name": "Johnny"
"age": 35
"height":1.83
}
result- source updated to:
{
"last_name":"Smith",
"first_name": "Johnny", - updated
"age": 35, - updated
"weight":79
"address": "567 Yonge Ave…" - updated
"height":1.83 - added
}
My solution:
declare @j_source varchar(200) = '{"first_name": "Smith", "last_name": "Smith","age": 28,"weight":79,"address": "123 Steels st…"}'
declare @j_update varchar(200) = '{"address": "567 Yonge Ave…","first_name": "Johnny","age": 35, "height":1.83}'
print @j_source
print @j_update
-- transform json to tables
select *
into #t_source
from openjson(@j_source)
select *
into #t_update
from openjson(@j_update)
-- combine the updated values with new values with non-updated values
select *
into #t_result
from
(
-- get key values that are not being updated
select ts.[key],ts.[value],ts.[type]
from #t_source as ts
left join #t_update as tu
on ts.[key] = tu.[key]
where tu.[key] is null
union -- get key values that are being updated. side note: the first and second select can be combined into one using isnull
select ts.[key],tu.[value],ts.[type] -- take value from #t_update
from #t_source as ts
inner join #t_update as tu
on ts.[key] = tu.[key]
union -- add new key values that does not exists in the source
select tu.[key],tu.[value],tu.[type] -- take value from #t_update
from #t_source as ts
right join #t_update as tu
on ts.[key] = tu.[key]
where ts.[key] is null
) as x
where [value] != '' -- remove key-value pair if the value is empty
/*
openjson type column data type
https://learn.microsoft.com/en-us/sql/t-sql/functions/openjson-transact-sql?view=sql-server-2017
type data-type
0 null
1 string
2 int
3 true/false
4 array
5 object
*/
-- transform table back to json in a generic way
select @j_source =
'{' +
STUFF((
select replace(',"x":','x', cast([key] as varchar(4000)) COLLATE SQL_Latin1_General_CP1_CI_AS)
+ case [type]
when 1 then replace('"z"','z',[value]) -- this is a string this is a text use double-quotes
when 2 then [value] -- this is int, don't use double-quotes
else ''
end
from #t_result
for xml PATH('')
), 1, 1, '')
+ '}'
print 'after update'
print @j_source
drop table #t_source
drop table #t_update
drop table #t_result
My solution works, but:
Likely will not work with arrays or nested json. Fine, doesn't bother me at this point.
I wonder if there is a more proper/affective/elegant way to do the entire solution, perhaps using json_modify ?
The order of the key-value pairs is not kept as the source, but I guess it's not a big deal.
Any normal way to convert key-value table back to json without explicitly defining columns and without the "garbage" that "for json auto" gives?
Code:
SELECT [key], [value]
FROM t_result
FOR JSON path, WITHOUT_ARRAY_WRAPPER
Output:
{"key":"address","value":"567 Yonge Ave…"},
{"key":"age","value":35}, {"key":"first_name","value":"Johnny"},
{"key":"height","value":1.83},{"key":"last_name","value":"Smith"}
UPDATE:
Based on Roman Pekar elegant solution, I've added another case to that solution to exclude quotes when the value is [type] = 2(int). When there are millions of records as in my case, additional quotes impacts storage.
create function dbo.fn_json_merge
(
@a nvarchar(max),
@b nvarchar(max)
)
returns nvarchar(max)
as
begin
if left(@a, 1) = '{' and left(@b, 1) = '{'
begin
select
@a = case
when d.[type] in (1,3) then json_modify(@a, concat('$.',d.[key]), d.[value])
else @a
end,
@a = case
when d.[type] in (2) and TRY_CAST(d.[value] AS int) is not null then json_modify(@a, concat('$.',d.[key]), cast(d.[value] as int))
when d.[type] in (2) and TRY_CAST(d.[value] AS int) is null then json_modify(@a, concat('$.',d.[key]), d.[value])
else @a
end,
@a = case
when d.[type] in (4,5) then json_modify(@a, concat('$.',d.[key]), json_query(d.[value]))
else @a
end
from openjson(@b) as d;
end
else if left(@a, 1) = '[' and left(@b, 1) = '{'
begin
select @a = json_modify(@a, 'append $', json_query(@b));
end
else
begin
select @a = concat('[', @a, ',', right(@b, len(@b) - 1));
end;
return @a;
end;
