Updating table based on JSON inside PostgreSQL function - sql

Question

I am writing a plpgsql function that should update a table based on a provided JSON object. The JSON contains a table representation with all the same columns as the table itself has.
The function currently looks as follows:
CREATE OR REPLACE FUNCTION update (updated json)
BEGIN
/* transfrom json to table */
WITH updated_vals AS (
SELECT
*
FROM
json_populate_recordset(NULL::my_table, updated)
),
/* Retrieve all columns from mytable and also with reference to updated_vals table */
cols AS (
SELECT
string_agg(quote_ident(columns), ',') AS table_cols,
string_agg('updated_vals.' || quote_ident($1), ',') AS updated_cols
FROM
information_schema
WHERE
table_name = 'my_table' -- table name, case sensitive
AND table_schema = 'public' -- schema name, case sensitive
AND column_name <> 'id' -- all columns except id and user_id
AND column_name <> 'user_id'
),
/* Define the table columns separately */
table_cols AS (
SELECT
table_cols
FROM
cols
),
/* Define the updated columns separately */
updated_cols AS (
SELECT
updated_cols
FROM
cols)
/* Execute the update statement */
EXECUTE 'UPDATE my_table'
|| ' SET (' || table_cols::text || ') = (' || updated_cols::text || ') '
|| ' FROM updated_vals '
|| ' WHERE my_table.id = updated_vals.id '
|| ' AND my_table.user_id = updated_vals.user_id';
COMMIT;
END;
I noticed that the combination of the WITH clause combined with the EXECUTE will always trigger the error syntax error at or near EXECUTE, even if those are very simple and straightforward. Is this indeed the case, and if so, what would be an alternative approach to provide the required variables (updated_vals, table_cols and updated_cols) to EXECUTE?
If you have any other improvements on this code I'd be happy to see those for I am very new to sql/plpgsql.

Answer 1

If you wrote table name (my_table) in your function, this means that you will update always only one specified table from JSON data. Because of this, you can write table names and column names in your function manually, not using information_schema. This is the simple and easy way.
For example:
CREATE OR REPLACE FUNCTION rbac.update_users_json(updated json)
RETURNS boolean
LANGUAGE plpgsql
AS $function$
begin
update rbac.users usr
set
username = jsn.username,
first_name = jsn.first_name,
last_name = jsn.last_name
from (
select * from json_populate_recordset(NULL::rbac.users, updated)
) jsn
where jsn.id = usr.id;
return true;
END;
$function$
;

Answer 2

For dynamic tables:
CREATE OR REPLACE FUNCTION rbac.update_users_json_dynamic(updated json)
RETURNS boolean
LANGUAGE plpgsql
AS $function$
declare
f record;
exec_sql text;
sep text;
begin
exec_sql = 'update rbac.users usr set ' || E'\n';
sep = '';
for f in
select clm.column_name
from
information_schema."tables" tbl
inner join
information_schema."columns" clm on
clm.table_name = tbl.table_name
and clm.table_schema = tbl.table_schema
where
tbl.table_schema = 'test'
and tbl.table_name = 'users'
and clm.column_name <> 'id'
loop
exec_sql = exec_sql || sep || f.column_name || ' = ' || 'jsn.' || f.column_name;
sep = ', ' || E'\n';
end loop;
exec_sql = exec_sql || E'\n' || 'from (select * from json_populate_recordset(NULL::rbac.users, ''' ||
updated::text || ''')) jsn ' || E'\n' || 'where jsn.id = usr.id';
execute exec_sql;
return true;
END;
$function$
;