如何在PostgreSQL 9.2.1中避免循环触发调用

Question

我有一张桌子:

CREATE TABLE field_data.soil_samples (
 pgid SERIAL NOT NULL,
 sample_id text,
 project_id text,
 utm_zone integer,
 utm_easting integer,
 utm_northing integer,
 wgs84_longitude double precision,
 wgs84_latitude double precision,
 yt_albers_geom geometry(Point,3578),
 CONSTRAINT soil_samples_pk PRIMARY KEY (pgid)
)

PostGIS 2.0几何体yt_albers_geom是使用触发器创建的,该触发器针对此表触发INSERTS.如果要插入的记录满足以下条件之一,则会生成几何体:

1. 两者wgs84_latitude和wgs84_longitude字段都不为空
2. 每个的utm_zone,utm_easting和utm_northing不为空

现在,我对如何进行更新以实现以下目标感到困惑:

1. 当更新是为了utm_zone,utm_easting或utm_northing,然后wgs_84_latitude,wgs84_longitude和yt_albers_geom被触发更新
2. 当对wgs84_latitude或进行更新时,wgs84_longitude所有utm_字段都会更新,以及yt_albers_geom.
3. 完成更新后yt_albers_geom,将更新所有坐标字段.

似乎这些触发器中的任何一个都会导致无限循环的触发器触发,对吗？

Answer 1

您可以使用标准触发器 执行此操作BEFORE UPDATE OF ... ON ....通知
手册CREATE TRIGGER:

只有在列出的列中至少有一列被提及为UPDATE命令的目标时,触发器才会触发.

进一步向下:

当列中的任何列在UPDATE命令的SET列表中列为目标时,将触发特定于列的触发器(使用UPDATE OF column_name语法定义的触发器).即使未触发触发器,列的值也可能会更改,因为不会考虑BEFORE UPDATE触发器对行内容所做的更改.

大胆强调我的.因此没有无限循环,因为触发器内的更新不会调用另一个触发器.

测试用例

创建测试表(简化,没有不相关的行):

CREATE TABLE soil_samples (
  pgid SERIAL PRIMARY KEY

 ,utm_zone integer
 ,utm_easting integer
 ,utm_northing integer

 ,wgs84_longitude double precision
 ,wgs84_latitude double precision

 ,yt_albers_geom double precision
);

第一个要求的虚拟触发器:

当更新是为了utm_zone,utm_easting或utm_northing,然后 wgs_84_latitude,wgs84_longitude和yt_albers_geom被触发更新.

CREATE OR REPLACE FUNCTION trg_upbef_utm()  RETURNS trigger AS
$func$
BEGIN
   NEW.wgs84_latitude  := NEW.wgs84_latitude + 10;
   NEW.wgs84_longitude := NEW.wgs84_longitude + 10;
   NEW.yt_albers_geom  := NEW.yt_albers_geom + 10;

   RETURN NEW;
END
$func$ LANGUAGE plpgsql;

CREATE TRIGGER upbef_utm
BEFORE UPDATE OF utm_zone, utm_easting, utm_northing ON soil_samples
FOR EACH ROW
WHEN (NEW.utm_zone     IS DISTINCT FROM OLD.utm_zone    OR
      NEW.utm_easting  IS DISTINCT FROM OLD.utm_easting OR
      NEW.utm_northing IS DISTINCT FROM OLD.utm_northing)  -- optional
EXECUTE PROCEDURE trg_upbef_utm();

该WHEN条款是可选的.在没有实际更改值时阻止触发器触发.

第二个要求的虚拟触发器:

当对wgs84_latitude或进行更新时,wgs84_longitude所有u tm_字段都会更新,以及yt_albers_geom.

CREATE OR REPLACE FUNCTION trg_upbef_wgs84()  RETURNS trigger AS
$func$
BEGIN
   NEW.utm_zone       := NEW.utm_zone + 100;
   NEW.utm_easting    := NEW.utm_easting + 100;
   NEW.utm_northing   := NEW.utm_northing + 100;
   NEW.yt_albers_geom := NEW.yt_albers_geom + 100;

   RETURN NEW;
END
$func$ LANGUAGE plpgsql;

CREATE TRIGGER upbef_wgs84
 BEFORE UPDATE OF wgs84_latitude, wgs84_longitude ON soil_samples
 FOR EACH ROW
 WHEN (NEW.wgs84_latitude  IS DISTINCT FROM OLD.wgs84_latitude OR
       NEW.wgs84_longitude IS DISTINCT FROM OLD.wgs84_longitude)  -- optional
 EXECUTE PROCEDURE trg_upbef_wgs84();

沿着这些方向触发第三个要求......

测试

INSERT INTO soil_samples VALUES (1, 1,1,1, 2,2, 3) RETURNING *;

触发upbef_utm:空更新,没有任何反应:

UPDATE soil_samples SET utm_zone = 1 RETURNING *;

更新实际更改:第二个触发器upbef_wgs84不会触发UPDATE OF utm_zone!

UPDATE soil_samples SET utm_zone = 0 RETURNING *;

触发器upbef_wgs84:

UPDATE soil_samples SET wgs84_latitude = 0 RETURNING *;

- > SQLfiddle演示.