问题
Is there a way to get the JSON of the only modified fields?
Now I use the following trigger but the entire line is printed in the changelog.
Example tables:
TABLE tbl_changelog (
tbl TEXT,
op TEXT,
new JSON,
old JSON
);
TABLE tbl_items (
f1 TEXT,
f2 TEXT
);
Trigger:
CREATE OR REPLACE FUNCTION changelog_procedure() RETURNS trigger AS $$
BEGIN
INSERT INTO tbl_changelog(tbl, op, new, old)
VALUES (TG_TABLE_NAME, TG_OP, row_to_json(NEW), row_to_json(OLD));
RETURN NULL;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER;
CREATE TRIGGER changelog_items
AFTER INSERT OR UPDATE OR DELETE ON tbl_items
FOR EACH ROW EXECUTE PROCEDURE changelog_procedure();
After inserting and uploaded f2 and f1 the changelog is the following:
tbl_changelog
------------------------------------------------------------------
tbl | op | new | old
------------------------------------------------------------------
tbl_items | INSERT | {f1: "aa", f2: "bb"} |
------------------------------------------------------------------
tbl_items | UPDATE | {f1: "aa", f2: "cc"} | {f1: "aa", f2: "bb"}
------------------------------------------------------------------
tbl_items | UPDATE | {f1: "dd", f2: "cc"} | {f1: "aa", f2: "cc"}
------------------------------------------------------------------
I would like to record only the changes, that is:
tbl_changelog
------------------------------------------------------------------
tbl | op | new | old
------------------------------------------------------------------
tbl_items | INSERT | {f1: "aa", f2: "bb"} |
------------------------------------------------------------------
tbl_items | UPDATE | {f2: "cc"} | {f2: "bb"}
------------------------------------------------------------------
tbl_items | UPDATE | {f1: "dd"} | {f1: "aa"}
------------------------------------------------------------------
回答1:
Your trigger function cannot work well, it produces the error while inserting a row:
ERROR: record "old" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
You should treat the three cases of INSERT
, UPDATE
and DELETE
separately:
create or replace function changelog_procedure()
returns trigger as $$
declare
json_new jsonb;
json_old jsonb;
begin
if tg_op = 'INSERT' then
json_new:= to_jsonb(new);
elsif tg_op = 'DELETE' then
json_old:= to_jsonb(old);
else
select jsonb_object_agg(new_key, new_value), jsonb_object_agg(old_key, old_value)
into json_new, json_old
from jsonb_each(to_jsonb(new)) as n(new_key, new_value)
join jsonb_each(to_jsonb(old)) as o(old_key, old_value)
on new_key = old_key and new_value <> old_value;
end if;
insert into tbl_changelog(tbl, op, new, old)
values (tg_table_name, tg_op, json_new, json_old);
return null;
end;
$$ language plpgsql;
来源:https://stackoverflow.com/questions/55875237/use-a-postgres-trigger-to-record-the-json-of-only-the-modified-fields