Postgres - Track changes - postgresql

Question

I want to track the history changes from my table, for that I created one history table, right now is saving old and new values, but I want to save in one column the fk from my regular table.
This is my history table:
CREATE TABLE IF NOT EXISTS sales.history (
history_id integer PRIMARY KEY NOT NULL,
mytable_id integer,
table_name varchar(30),
new_val json,
old_val json,
operation varchar(10),
CONSTRAINT "fk sales.mytable_id to history.mytable_id" FOREIGN KEY (mytable_id) REFERENCES sales.sales (mytable_id)
) TABLESPACE pg_default;
I created a trigger to track update,insert and delete
CREATE TRIGGER t_history BEFORE INSERT OR UPDATE OR DELETE ON sales.sales
FOR EACH ROW EXECUTE PROCEDURE core.func_store_history_changes();
Now my function
CREATE OR REPLACE FUNCTION core.func_store_history_changes() RETURNS trigger AS $$
BEGIN
IF TG_OP = 'INSERT'
THEN
INSERT INTO sales.history (tabname, schemaname, operation, new_val)
VALUES (TG_RELNAME, TG_TABLE_SCHEMA, TG_OP, row_to_json(NEW));
RETURN NEW;
ELSIF TG_OP = 'UPDATE'
THEN
INSERT INTO sales.history (tabname, schemaname, operation, new_val, old_val)
VALUES (TG_RELNAME, TG_TABLE_SCHEMA, TG_OP,
row_to_json(NEW), row_to_json(OLD));
RETURN NEW;
ELSIF TG_OP = 'DELETE'
THEN
INSERT INTO sales.history (tabname, schemaname, operation, old_val)
VALUES (TG_RELNAME, TG_TABLE_SCHEMA, TG_OP, row_to_json(OLD));
RETURN OLD;
END IF;
END;
$$ LANGUAGE 'plpgsql' SECURITY DEFINER;
As you can see my history table has mytable_id which is a foreign key and primary key from sales table, how i can get that value and insert into my history table?
Regards

Answer 1

For you specific problem, I guess that you could use NEW.mytable_id and use trigger AFTER INSERT ...
Here is a example, I've wrote only the first if (INSERT).
CREATE TABLE IF NOT EXISTS sales.history (
history_id serial PRIMARY KEY NOT NULL,
mytable_id integer,
table_name varchar(30),
new_val json,
old_val json,
operation varchar(10),
CONSTRAINT "fk sales.mytable_id to history.mytable_id" FOREIGN KEY (mytable_id) REFERENCES sales.sales (mytable_id)
) TABLESPACE pg_default;
CREATE TRIGGER t_history AFTER INSERT OR UPDATE OR DELETE ON sales.sales
FOR EACH ROW EXECUTE PROCEDURE core.func_store_history_changes();
CREATE OR REPLACE FUNCTION core.func_store_history_changes() RETURNS trigger AS $$
BEGIN
IF TG_OP = 'INSERT'
THEN
INSERT INTO sales.history (table_name, operation,mytable_id, new_val)
VALUES (TG_RELNAME, TG_OP, NEW.mytable_id, row_to_json(NEW));
RETURN NEW;
ELSIF TG_OP = 'UPDATE'
THEN
INSERT INTO sales.history (tabname, schemaname, operation, new_val, old_val)
VALUES (TG_RELNAME, TG_TABLE_SCHEMA, TG_OP,
row_to_json(NEW), row_to_json(OLD));
RETURN NEW;
ELSIF TG_OP = 'DELETE'
THEN
INSERT INTO sales.history (tabname, schemaname, operation, old_val)
VALUES (TG_RELNAME, TG_TABLE_SCHEMA, TG_OP, row_to_json(OLD));
RETURN OLD;
END IF;
END;
$$ LANGUAGE 'plpgsql' SECURITY DEFINER;
Result:
# insert into sales.sales (value) values ('2.3');
INSERT 0 1
# select * from sales.sales;
mytable_id | value
------------+-------
5 | 2.30
(2 rows)
# select * from sales.history;
history_id | mytable_id | table_name | new_val | old_val | operation
------------+------------+------------+-------------------------------+---------+-----------
3 | 5 | sales | {"mytable_id":5,"value":2.30} | | INSERT
(2 rows)
But, maybe, you could try to use this generic trigger for any table.
https://github.com/2ndQuadrant/audit-trigger