Postgres 12

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CREATE TABLE pipes (id int, geom geometry(multilinestring),node_id_dwn_str int, node_id_up_str int);
CREATE TABLE structures (node_id int, geom geometry(multipoint));

INSERT INTO structures VALUES 
(1,'0104000020950B00000100000001010000001026FA48113B07410D6A8412CF1D3D41'),
(2,'0104000020950B0000010000000101000000BA1BF246E6DD0741D064CB58C2E43C41');
2 rows affected

CREATE OR REPLACE FUNCTION insert_pipe() RETURNS TRIGGER AS $$
BEGIN
  SELECT 
  j.node_id,
  i.node_id
  INTO NEW.dwn_str, NEW.up_str
  FROM ST_Dump(ST_SetSRID(NEW.geom,2346)) dump_line,
  LATERAL (SELECT s.node_id,(ST_SetSRID(s.geom,2346)) 
		   FROM structures s
	       ORDER BY ST_EndPoint((dump_line).geom)<->(ST_SetSRID(s.geom,2346)) 
		   LIMIT 1) j (node_id,geom_closest_downstream),
  LATERAL (SELECT s.node_id,(ST_SetSRID(s.geom,2346))
		   FROM structures s
	       ORDER BY ST_StartPoint((dump_line).geom)<->(ST_SetSRID(s.geom,2346)) 
		   LIMIT 1) i (node_id,geom_closest_upstream);
		   
  RETURN NEW;
END; $$ LANGUAGE plpgsql;

CREATE TRIGGER t_insert_pipe 
BEFORE INSERT OR UPDATE ON pipes FOR EACH ROW EXECUTE PROCEDURE insert_pipe();
INSERT INTO pipes VALUES 
(1,'0105000020950B00000100000001020000000200000046243EC3282608418D28242D6C1B3D4128531BE88A2608418284B3EF561B3D41'),
(2,'0105000020950B0000010000000102000000020000004ABF2CBC86B108413B93650696323D413C487924CCB10841925D490495323D41');
ERROR:  record "new" has no field "dwn_str"
CONTEXT:  PL/pgSQL function insert_pipe() line 3 at SQL statement


SELECT * FROM pipes;