Business Logic

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How much business logic should we put in the database?

Let’s query the chinook database for an artist’s albums and total duration of each album:

select album.title as album
    sum(milliseconds) * interval '1ms' as duration
    from album
        join artist using(artistid)
        left join track using (albumid)
    where artist.name = 'Red Hot Chili Peppers'
group by album
order by album;

Correctness

There are four isolation levels in Postgres:

Read uncommitted:
Read committed:
- This allows transactions to see the results of other transactions as soon as they are committed.
Repeatable Read
- Your transaction uses the same snapshot of the whole database for its entire duration, from BEGIN to COMMIT. This means that even if a transaction is going on in the background, it won’t affect this query.
Serializable
- This guarantees that there is a one-transaction-at-a-time ordering of what query was run.

Stored Procedures

We can create a function that will allow us to do the same query but with the artist_id.

create or replace function get_all_albums
(
    in artistid bigint,
    out album text,
    out duration interval
);
returns setof record
language sql
as $$
    select album.title as album,
    sum(milliseconds) * interval '1 ms' as duration
    from album
        join artist using(artistid)
        left join track using(albumid)
        where artist.artistid = get_all_albums.artistid
group by album
order by album;
$$

try to use SQL only instead of PLpgSQL, although you can do that if necessary.

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business-logic

Table of Contents

Business Logic

Correctness

Stored Procedures