How to repeat SQL insertion until successful with pg-promise?

In my program I insert some data into a table and get back it's id and I need to ensure I enter that id into another table with a unique randomly generated string. But, in case the insertion fails for attempting to insert a already-existing random string, how could I repeat the insertion until it is successful?

I'm using pg-promise to talk to postgreSQL. I can run program like this that inserts the data into both tables given the random string doesn't already exists:

   db.none(
            `
            WITH insert_post AS
            (
                INSERT INTO table_one(text) VALUES('abcd123')
                RETURNING id
            )
            INSERT INTO table_two(id, randstr)
                    VALUES((SELECT id FROM insert_post), '${randStrFn()}')
            `
        )
    .then(() => console.log("Success"))
    .catch(err => console.log(err));

I'm unsure if there is any easy SQL/JS/pg-promise based solution that I could make use of.

via Robert C. Holland