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Create contrib/bool_plperl to provide a bool transform for PL/Perl[U].

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plperl's default handling of bool arguments or results is not terribly
satisfactory, since Perl doesn't consider the string 'f' to be false.
Ideally we'd just fix that, but the backwards-compatibility hazard
would be substantial.  Instead, build a TRANSFORM module that can
be optionally applied to provide saner semantics.

Perhaps usefully, this is also about the minimum possible skeletal
example of a plperl transform module; so it might be a better starting
point for user-written transform modules than hstore_plperl or
jsonb_plperl.

Ivan Panchenko

Discussion: https://postgr.es/m/1583013317.881182688@f390.i.mail.ru
This commit is contained in:
Tom Lane
2020-03-06 17:11:23 -05:00
parent a6525588b7
commit 36058a3c55
14 changed files with 502 additions and 4 deletions
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47
doc/src/sgml/plperl.sgml
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@ -55,8 +55,11 @@
syntax:
<programlisting>
CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
# PL/Perl function body
CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>)
RETURNS <replaceable>return-type</replaceable>
-- function attributes can go here
AS $$
# PL/Perl function body goes here
$$ LANGUAGE plperl;
</programlisting>
@ -188,6 +191,39 @@ $$ LANGUAGE plperl;
escape binary data for a return value of type <type>bytea</type>.
</para>
<para>
One case that is particularly important is boolean values. As just
stated, the default behavior for <type>bool</type> values is that they
are passed to Perl as text, thus either <literal>'t'</literal>
or <literal>'f'</literal>. This is problematic, since Perl will not
treat <literal>'f'</literal> as false! It is possible to improve matters
by using a <quote>transform</quote> (see
<xref linkend="sql-createtransform"/>). Suitable transforms are provided
by the <filename>bool_plperl</filename> extension. To use it, install
the extension:
<programlisting>
CREATE EXTENSION bool_plperl; -- or bool_plperlu for PL/PerlU
</programlisting>
Then use the <literal>TRANSFORM</literal> function attribute for a
PL/Perl function that takes or returns <type>bool</type>, for example:
<programlisting>
CREATE FUNCTION perl_and(bool, bool) RETURNS bool
TRANSFORM FOR TYPE bool
AS $$
my ($a, $b) = @_;
return $a &amp;&amp; $b;
$$ LANGUAGE plperl;
</programlisting>
When this transform is applied, <type>bool</type> arguments will be seen
by Perl as being <literal>1</literal> or empty, thus properly true or
false. If the function result is type <type>bool</type>, it will be true
or false according to whether Perl would evaluate the returned value as
true.
Similar transformations are also performed for boolean query arguments
and results of SPI queries performed inside the function
(<xref linkend="plperl-database"/>).
</para>
<para>
Perl can return <productname>PostgreSQL</productname> arrays as
references to Perl arrays. Here is an example:
@ -382,6 +418,13 @@ use strict;
commands will accept any string that is acceptable input format
for the function's declared return type.
</para>
<para>
If this behavior is inconvenient for a particular case, it can be
improved by using a transform, as already illustrated
for <type>bool</type> values. Several examples of transform modules
are included in the <productname>PostgreSQL</productname> distribution.
</para>
</sect1>
<sect1 id="plperl-builtins">