On Wed, 13 Dec 2006, Erik Jones wrote:
Marc Evans wrote:
On Wed, 13 Dec 2006, Erik Jones wrote:
Marc Evans wrote:
Hi -
I am struggling with a trigger function in plpgsql, and am hoping that
someone on this list can't show me a way to do what I need.
In the trigger, TG_ARGV[0] is the name of a column that I want to
evaluate. This code shows the concept, though is not functional:
CREATE OR REPLACE FUNCTION foo() RETURNS TRIGGER AS $$
DECLARE
column_name TEXT := TG_ARGV[0];
data TEXT;
BEGIN
EXECUTE 'SELECT NEW.' || column_name INTO data;
-- ...
END;
$$ LANGUAGE plpgsql;
When I try to use that code, I receive:
c3i=> insert into test_table values (1,1);
ERROR: NEW used in query that is not in a rule
CONTEXT: SQL statement "SELECT NEW.magic"
How can I get the value of NEW.{column_name} (aka NEW.magic in this
specific test case) into the variable data?
EXECUTE 'SELECT ' || NEW.column_name ';' INTO data;
Thanks for the suggestion. Unfortunately, it does not work:
CREATE OR REPLACE FUNCTION foo() RETURNS TRIGGER AS $$
DECLARE
column_name TEXT := TG_ARGV[0];
data TEXT;
BEGIN
EXECUTE 'SELECT ' || NEW.column_name || ';' INTO date;
-- ...
END;
$$ LANGUAGE plpgsql;
c3i=> insert into test_table values (1,1);
ERROR: record "new" has no field "column_name"
Ah, sorry, I'd just arrived at work and wasn't quite away as of yet. AFAIK,
plpgsql doesn't have any facilities for variable substitution in variable
names (called variable variables in some languages). However, if plpgsql is
your only procedural option (plperl, I've heard, does support this feature)
and the possible values for column name are known to you, there is a hackish
workaround:
IF(column_name = 'foo') THEN
EXECUTE 'SELECT ' || NEW.foo || ';' INTO data;
ELSIF(column_name = 'bar') THEN
EXECUTE 'SELECT ' || NEW.bar || ';' INTO data;
ELSIF
.
.
.
You get the picture...
Thanks for the suggestion. I would be quiet content to use plperl, if I
could figure out a way to do the equivilant of plpgsql's:
EXECUTE 'INSERT INTO ' || table_name || ' VALUES(NEW.*)';
I suppsoe that in plperl I could walk the list of keys in $_TD->{new}
building a list of columns and values that are then placed in a
spi_prepare. Would that be the recommended technique?
- Marc
