Let's say I have two tables like this (I'm leaving stuff out for
simplicity):
CREATE SEQUENCE HOMETOWN_SEQ_GEN START 1 INCREMENT 1;
CREATE TABLE hometowns (
id INTEGER DEFAULT nextval('HOMETOWN_SEQ_GEN'),
name VARCHAR,
PRIMARY KEY (id),
UNIQUE(name)
);
CREATE SEQUENCE USER_SEQ_GEN START 1 INCREMENT 1;
CREATE TABLE users (
id BIGINT DEFAULT nextval('USER_SEQ_GEN'),
hometown_id INTEGER,
name VARCHAR NOT NULL,
PRIMARY KEY (id),
FOREIGN KEY (hometown_id) REFERENCES hometowns(id)
);
The hometowns table is populate as users are created. For example, a
client may submit {"name":"Robert", "hometown":"Portland"}.
The hometowns table will never be updated, only either queries or inserted.
So given this I need to INSERT a row into "users" and either SELECT the
hometowns.id that matches "Portland" or if it doesn't exist I INSERT it
returning the hometowns.id".
Normally I would do by first doing a SELECT on hometown. If I don't get
anything I do an INSERT into hometown RETURNING the id. If THAT throws an
error then I do the SELECT again. Now I'm finally ready to INSERT into
users using the hometowns.id from the above steps.
But wow, that seems like a lot of code for a simple "Add if doesn't exist"
foreign key relationship -- but this is how I've always done.
So my question. Is there a simpler, more performant, or thread-safe way to
do this?
Thanks!
