PostgreSQL use uuid_generate_v4() used in INSERT...SELECT in a later UPDATE statement - postgresql

Question

I'm writing a database migration that adds a new table whose id column is populated using uuid_generate_v4(). However, that generated id needs to be used in an UPDATE on another table to associate the entities. Here's an example:
BEGIN;
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
CREATE TABLE IF NOT EXISTS models(
id,
type
);
INSERT INTO models(id)
SELECT
uuid_generate_v4() AS id
,t.type
FROM body_types AS t WHERE t.type != "foo";
ALTER TABLE body_types
ADD COLUMN IF NOT EXISTS model_id uuid NOT NULL DEFAULT uuid_generate_v4();
UPDATE TABLE body_types SET model_id =
(SELECT ....??? I'M STUCK RIGHT HERE)
This is obviously a contrived query with flaws, but I'm trying to illustrate that what it looks like I need is a way to store the uuid_generate_v4() value from each inserted row into a variable or hash that I can reference in the later UPDATE statement.
Maybe I've modeled the solution wrong & there's a better way? Maybe there's a postgresql feature I just don't know about? Any pointers greatly appreciated.

Answer 1

I was modeling the solution incorrectly. The short answer is "don't make the id in the INSERT random". In this case the key is to add the 'model_id' column to 'body_types' first. Then I can use it in the INSERT...SELECT without having to save it for later use because I'll be selecting it from the body_types table.
BEGIN;
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
ALTER TABLE body_types
ADD COLUMN IF NOT EXISTS model_id uuid NOT NULL DEFAULT uuid_generate_v4();
CREATE TABLE IF NOT EXISTS models(
id,
type
);
INSERT INTO models(id)
SELECT
t.model_id AS id
,t.type
FROM body_types AS t WHERE t.type != "foo";
Wish I had a better contrived example, but the point is, avoid using random values that you have to use later, and in this case it was totally unnecessary to do so anyway.