Insert same UUID into two tables (once as primary key, once as foreign key) in one statement - postgresql

Question

Consider the postgres view which joins together two tables table_geom and table_data by the field id_data (id_data being the primary key of table_data and a foreign key in table_geom):
CREATE OR REPLACE VIEW myschema.view AS
SELECT table_geom.geom, table_geom.id_geom, table_geom.id_data,
table_data.id_data, table_data.data
FROM myschema.table_geom, myschema.table_data
WHERE table_geom.id_data = table_data.id_data;
id_geom and id_data are UUIDs. I'd like to autogenerate them on insert using uuid_generate_v4() with a rule such as
CREATE OR REPLACE RULE view_insert_rule AS
ON INSERT TO myschema.view DO INSTEAD (
INSERT INTO myschema.table_geom (geom, id_geom, id_data) VALUES (new.geom, (select uuid_generate_v4()), $ID_DATA$);
INSERT INTO myschema.table_data (id_data, data) VALUES ($ID_DATA$, new.data);
);
Problem: $ID_DATA$ needs to be the same UUID when inserting into the two tables.
One attempt was
CREATE OR REPLACE RULE view_insert_rule AS
ON INSERT TO myschema.view DO INSTEAD (
WITH ins_data as (
INSERT INTO myschema.table_data (id_data, data) VALUES ((select uuid_generate_v4()), new.data) RETURNING id_data
)
INSERT INTO myschema.table_geom (geom, id_geom, id_data) VALUES (new.geom, (select uuid_generate_v4()), ins_data.id_data);
);
which however does not work due to ERROR: cannot refer to NEW within WITH query.
Any idea how write such an insert rule?

Answer 1

Since you are doing an INSERT on a view, the recommended procedure is an INSTEAD OF INSERT trigger on the view. In the trigger function you rewrite the insert on the view into two inserts on the underlying tables:
CREATE FUNCTION insert_new_uuids() RETURNS trigger AS $$
DECLARE
new_id uuid;
BEGIN
new_id := uuid_generate_v4();
INSERT INTO myschema.table_data (id_data, data) VALUES (new_id, NEW.data);
INSERT INTO myschema.table_geom (geom, id_geom, id_data) VALUES (NEW.geom, uuid_generate_v4(), new_id);
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER ins_view
INSTEAD OF INSERT ON myschema."view"
FOR EACH ROW EXECUTE PROCEDURE insert_new_uuids();