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><A
NAME="PLPERL-TRIGGERS"
>41.6. PL/Perl Triggers</A
></H1
><P
> PL/Perl can be used to write trigger functions. In a trigger function,
the hash reference <TT
CLASS="VARNAME"
>$_TD</TT
> contains information about the
current trigger event. <TT
CLASS="VARNAME"
>$_TD</TT
> is a global variable,
which gets a separate local value for each invocation of the trigger.
The fields of the <TT
CLASS="VARNAME"
>$_TD</TT
> hash reference are:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>$_TD->{new}{foo}</TT
></DT
><DD
><P
> <TT
CLASS="LITERAL"
>NEW</TT
> value of column <TT
CLASS="LITERAL"
>foo</TT
>
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{old}{foo}</TT
></DT
><DD
><P
> <TT
CLASS="LITERAL"
>OLD</TT
> value of column <TT
CLASS="LITERAL"
>foo</TT
>
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{name}</TT
></DT
><DD
><P
> Name of the trigger being called
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{event}</TT
></DT
><DD
><P
> Trigger event: <TT
CLASS="LITERAL"
>INSERT</TT
>, <TT
CLASS="LITERAL"
>UPDATE</TT
>,
<TT
CLASS="LITERAL"
>DELETE</TT
>, <TT
CLASS="LITERAL"
>TRUNCATE</TT
>, or <TT
CLASS="LITERAL"
>UNKNOWN</TT
>
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{when}</TT
></DT
><DD
><P
> When the trigger was called: <TT
CLASS="LITERAL"
>BEFORE</TT
>,
<TT
CLASS="LITERAL"
>AFTER</TT
>, <TT
CLASS="LITERAL"
>INSTEAD OF</TT
>, or
<TT
CLASS="LITERAL"
>UNKNOWN</TT
>
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{level}</TT
></DT
><DD
><P
> The trigger level: <TT
CLASS="LITERAL"
>ROW</TT
>, <TT
CLASS="LITERAL"
>STATEMENT</TT
>, or <TT
CLASS="LITERAL"
>UNKNOWN</TT
>
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{relid}</TT
></DT
><DD
><P
> OID of the table on which the trigger fired
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{table_name}</TT
></DT
><DD
><P
> Name of the table on which the trigger fired
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{relname}</TT
></DT
><DD
><P
> Name of the table on which the trigger fired. This has been deprecated,
and could be removed in a future release.
Please use $_TD->{table_name} instead.
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{table_schema}</TT
></DT
><DD
><P
> Name of the schema in which the table on which the trigger fired, is
</P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD->{argc}</TT
></DT
><DD
><P
> Number of arguments of the trigger function
</P
></DD
><DT
><TT
CLASS="LITERAL"
>@{$_TD->{args}}</TT
></DT
><DD
><P
> Arguments of the trigger function. Does not exist if <TT
CLASS="LITERAL"
>$_TD->{argc}</TT
> is 0.
</P
></DD
></DL
></DIV
><P>
</P
><P
> Row-level triggers can return one of the following:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>return;</TT
></DT
><DD
><P
> Execute the operation
</P
></DD
><DT
><TT
CLASS="LITERAL"
>"SKIP"</TT
></DT
><DD
><P
> Don't execute the operation
</P
></DD
><DT
><TT
CLASS="LITERAL"
>"MODIFY"</TT
></DT
><DD
><P
> Indicates that the <TT
CLASS="LITERAL"
>NEW</TT
> row was modified by
the trigger function
</P
></DD
></DL
></DIV
><P>
</P
><P
> Here is an example of a trigger function, illustrating some of the
above:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE test (
i int,
v varchar
);
CREATE OR REPLACE FUNCTION valid_id() RETURNS trigger AS $$
if (($_TD->{new}{i} >= 100) || ($_TD->{new}{i} <= 0)) {
return "SKIP"; # skip INSERT/UPDATE command
} elsif ($_TD->{new}{v} ne "immortal") {
$_TD->{new}{v} .= "(modified by trigger)";
return "MODIFY"; # modify row and execute INSERT/UPDATE command
} else {
return; # execute INSERT/UPDATE command
}
$$ LANGUAGE plperl;
CREATE TRIGGER test_valid_id_trig
BEFORE INSERT OR UPDATE ON test
FOR EACH ROW EXECUTE PROCEDURE valid_id();</PRE
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