Postgres auto insert with previous values if some data misses - postgresql

Question

I have data with date range, some date wont come for few days, during the missed window I just want to insert the previous data.
Is there way to take care of this during insert of data it self
For example
create table foo (ID VARCHAR(10), foo_count int, actual_date date);
insert into foo ( values('234534', 100, '2017-01-01'),('234534', 200, '2017-01-02'));
insert into foo ( values('234534', 300, '2017-01-03') );
insert into foo ( values('234534', 300, '2017-01-08') );
After the last insert I can make sure previous data gets generated
So it should look something like this
ID | foo_count | actual_date
-----------+-----------------+------------
234534 | 100 | 2017-01-01
234534 | 200 | 2017-02-01
234534 | 300 | 2017-03-01
234534 | 300 | 2017-04-01
234534 | 300 | 2017-05-01
234534 | 300 | 2017-06-01
234534 | 180 | 2017-07-01
I am using JPA to insert it, currently I query the table and see the current date in the table and populate the missing data

Answer 1

I would think about a better INSERT statement. Inserting from a SELECT statement would make things easier. The SELECT statement could be used to generate the requested date series.
INSERT INTO foo
SELECT
--<advanced query>
However, I guess, that's not simply possible since you are not using the JDBC directly or want to use native queries for inserting your data.
In that case, you could install a trigger to your database which could do the magic:
demo:db<>fiddle
Trigger function:
CREATE FUNCTION insert_missing()
RETURNS TRIGGER AS
$$
DECLARE
max_record record;
BEGIN
SELECT -- 1
id,
foo_count,
actual_date
FROM
foo
ORDER BY actual_date DESC
LIMIT 1
INTO max_record;
IF (NEW.actual_date - 1 > max_record.actual_date) THEN -- 2
INSERT INTO foo
SELECT
max_record.id,
max_record.foo_count,
generate_series(max_record.actual_date + 1, NEW.actual_date - 1, interval '1 day'); -- 3
END IF;
RETURN NEW;
END;
$$ language 'plpgsql';
Query the record with the current maximum date.
If the maximum date is more than one day before the new date...
... Insert a date series (from day after current max date until the date before the new one). This can be generated with generate_series().
Afterwards create the ON BEFORE INSERT trigger:
CREATE TRIGGER insert_missing
BEFORE INSERT
ON foo
FOR EACH ROW
EXECUTE PROCEDURE insert_missing();