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Add some documentation about PL/Python limitations

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suggested by Steve White (bug #5272)
This commit is contained in:
Peter Eisentraut 2010-03-29 21:20:58 +00:00
parent de66effede
commit 51d2c9b0bb
1 changed files with 28 additions and 2 deletions
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doc/src/sgml/plpython.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpython.sgml,v 1.47 2010/03/21 02:24:29 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpython.sgml,v 1.48 2010/03/29 21:20:58 petere Exp $ -->
<chapter id="plpython">
<title>PL/Python - Python Procedural Language</title>
@ -243,7 +243,7 @@ $$ LANGUAGE plpythonu;
</para>
</sect1>
<sect1>
<sect1 id="plpython-data">
<title>Data Values</title>
<para>
Generally speaking, the aim of PL/Python is to provide
@ -364,6 +364,18 @@ $$ LANGUAGE plpythonu;
return type and the Python data type of the actual return object
are not flagged; the value will be converted in any case.
</para>
<tip>
<para>
<application>PL/Python</application> functions cannot return
either type <type>RECORD</type> or <type>SETOF RECORD</type>. A
workaround is to write a <application>PL/pgSQL</application>
function that creates a temporary table, have it call the
<application>PL/Python</application> function to fill the table,
and then have the <application>PL/pgSQL</application> function
return the generic <type>RECORD</type> from the temporary table.
</para>
</tip>
</sect2>
<sect2>
@ -866,6 +878,20 @@ rv = plpy.execute(plan, [ "name" ], 5)
The third argument is the limit and is optional.
</para>
<para>
Query parameters and result row fields are converted between
PostgreSQL and Python data types as described
in <xref linkend="plpython-data">. The exception is that composite
types are currently not supported: They will be rejected as query
parameters and are converted to strings when appearing in a query
result. As a workaround for the latter problem, the query can
sometimes be rewritten so that the composite type result appears as
a result row rather than as a field of the result row.
Alternatively, the resulting string could be parsed apart by hand,
but this approach is not recommended because it is not
future-proof.
</para>
<para>
When you prepare a plan using the PL/Python module it is
automatically saved. Read the SPI documentation (<xref