Обсуждение:

In PL/pgSQL, is there a way to put a *variable* column-name in a dot
notation reference to a RECORD column?

For example, suppose I want to write a function like the following, which is
to be called by a "BEFORE INSERT" trigger:

CREATE OR REPLACE FUNCTION foo (  ) RETURNS TRIGGER AS    '   DECLARE        var VARCHAR;   BEGIN       var :=
TG_ARGV[0]             NEW.<the column whose name is the value of var> := ''whatever'';       RETURN NEW;        END;
'  LANGUAGE 'plpgsql' 
;

The aim of this uninteresting function is to assign the value 'whatever' to
the table column that is passed in by the calling trigger as TG_ARGV[0],
i.e. the first calling argument.

What I don't know is what to put into the dot notation in place of ".<the
column whose name is the value of var>" so that the column of NEW that is
addressed by the assignment statement is the one passed in as the first
argument.  Is there any PL/pgSQL construct that could be substituted in here
to achieve this result?

If not, can anybody suggest a way to write a trigger-called function that
would accomplish the same result?

In case it's not obvious, the underlying goal is to write a single
trigger-called function that could modify different columns for each trigger
that called it, where each trigger specified the target column by a calling
argument (or by any other viable mechanism).

~ TIA
~ Ken

On Wed, 2005-11-23 at 23:23 -0500, Ken Winter wrote:
> In PL/pgSQL, is there a way to put a *variable* column-name in a dot
> notation reference to a RECORD column?
> 
> For example, suppose I want to write a function like the following, which is
> to be called by a "BEFORE INSERT" trigger:
> 
> CREATE OR REPLACE FUNCTION foo (  ) RETURNS TRIGGER AS 
>     '
>     DECLARE 
>         var VARCHAR;
>     BEGIN
>         var := TG_ARGV[0]       
>         NEW.<the column whose name is the value of var> := ''whatever'';
>         RETURN NEW;     
>     END;
>     '
>     LANGUAGE 'plpgsql'
> ;
> 
> The aim of this uninteresting function is to assign the value 'whatever' to
> the table column that is passed in by the calling trigger as TG_ARGV[0],
> i.e. the first calling argument.  
> 
> What I don't know is what to put into the dot notation in place of ".<the
> column whose name is the value of var>" so that the column of NEW that is
> addressed by the assignment statement is the one passed in as the first
> argument.  Is there any PL/pgSQL construct that could be substituted in here
> to achieve this result?

Unfortunately not.

> If not, can anybody suggest a way to write a trigger-called function that
> would accomplish the same result?

You would have to do something like:

CREATE OR REPLACE FUNCTION foo() RETURNS TRIGGER AS    $$   DECLARE        var VARCHAR;   BEGIN       var :=
TG_ARGV[0];      IF var = 'column_1' THEN           NEW.column_1 = 'whatever';       ELSIF var = 'column_2' THEN
  NEW.column_2 = 'whatever';       ...       END IF;       RETURN NEW;  END;  $$  LANGUAGE plpgsql;
 

Oliver Elphick

O Oliver Elphick έγραψε στις Nov 24, 2005 :

> On Wed, 2005-11-23 at 23:23 -0500, Ken Winter wrote:
> > In PL/pgSQL, is there a way to put a *variable* column-name in a dot
> > notation reference to a RECORD column?

You can do it with a C function.
(See dbmirror's pending.c for a reference)

> 

-- 
-Achilleus