PostgreSQL Update trigger

Question

I have a table:

CREATE TABLE annotations
(
  gid serial NOT NULL,
  annotation character varying(250),
  the_geom geometry,
  "rotationAngle" character varying(3) DEFAULT 0,
  CONSTRAINT annotations_pkey PRIMARY KEY (gid),
  CONSTRAINT enforce_dims_the_geom CHECK (st_ndims(the_geom) = 2),
  CONSTRAINT enforce_srid_the_geom CHECK (st_srid(the_geom) = 4326)
)

And trigger:

CREATE TRIGGER set_angle
AFTER INSERT OR UPDATE
ON annotations
FOR EACH ROW
EXECUTE PROCEDURE setangle();

And function:

CREATE OR REPLACE FUNCTION setAngle() RETURNS TRIGGER AS $$
BEGIN
IF    TG_OP = 'INSERT' THEN
    UPDATE annotations SET "rotationAngle" = degrees( ST_Azimuth( ST_StartPoint(NEW.the_geom), ST_EndPoint(NEW.the_geom) ) )-90 WHERE gid = NEW.gid;
    RETURN NEW;
ELSIF TG_OP = 'UPDATE' THEN
    UPDATE annotations SET "rotationAngle" = degrees( ST_Azimuth( ST_StartPoint(NEW.the_geom), ST_EndPoint(NEW.the_geom) ) )-90 WHERE gid = NEW.gid;
    RETURN NEW;
END IF;
END;
$$ LANGUAGE plpgsql;

And when new row inserted in table or row edited i want to field rotationAngle setted with function result. But when i inserting a new row in table function not work. I mean thath rotationAngle value not changed.

What can be wrong?

Answer 1

As @SpartanElite pointed out, you are triggering an endless loop.

Simplify the trigger function:

CREATE OR REPLACE FUNCTION set_angle()
  RETURNS TRIGGER AS
$func$
BEGIN
   NEW."rotationAngle" := degrees(
                             ST_Azimuth(
                                ST_StartPoint(NEW.the_geom)
                              , ST_EndPoint(NEW.the_geom)
                             )
                          ) - 90;
   RETURN NEW;
END
$func$ LANGUAGE plpgsql;

• Assign to NEW directly. No WHERE in this case.
• You must double-quote illegal column names. Better not to use such names to begin with.
  Recent related answer.
• Code for insert & upgrade is the same. I folded into one code path.

Use a BEFORE trigger. This way you can edit columns of the triggering row directly before they are saved:

CREATE TRIGGER set_angle
BEFORE INSERT OR UPDATE ON annotations
FOR EACH ROW EXECUTE PROCEDURE set_angle();

However

If you are just trying to persist a functionally dependent value in the table (and there are no other considerations): Don't. Use a view or a generated column instead:

• Store common query as column?

Then you don't need any of this.