Upsert with a transaction

Question

I\'m using Spring with PostgreSQL and I try to do a sort of UPSERT by using a code like this:

jt.update(\"delete from A where id = 1\")
jt.update(\"insert in         


        

Answer 1

Assuming this simple table:

CREATE TABLE tbl(id int primary key, value int);

This function almost 100% secure (see comments) for concurrent transactions.:

CREATE OR REPLACE FUNCTION f_upsert(_id int, _value int)
  RETURNS void AS
$func$
BEGIN
LOOP
   UPDATE tbl SET value = _value WHERE  id = _id;

   EXIT WHEN FOUND;

   BEGIN
      INSERT INTO tbl (id, value)
      VALUES (_id, _value);

      RETURN;

   EXCEPTION WHEN UNIQUE_VIOLATION THEN     -- tbl.id has UNIQUE constraint.
      RAISE NOTICE 'It actually happened!'; -- hardly ever happens
   END;

END LOOP;
END
$func$ LANGUAGE plpgsql;

Call:

SELECT f_upsert(2, 2);

It's very similar to this INSERT / SELECT case with more explanation and links:

• Is SELECT or INSERT in a function prone to race conditions?