codekingpro/portable-devtools

1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>59.1. Foreign Data Wrapper Functions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="fdwhandler.html" title="Chapter 59. Writing a Foreign Data Wrapper" /><link rel="next" href="fdw-callbacks.html" title="59.2. Foreign Data Wrapper Callback Routines" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">59.1. Foreign Data Wrapper Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="fdwhandler.html" title="Chapter 59. Writing a Foreign Data Wrapper">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="fdwhandler.html" title="Chapter 59. Writing a Foreign Data Wrapper">Up</a></td><th width="60%" align="center">Chapter 59. Writing a Foreign Data Wrapper</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="fdw-callbacks.html" title="59.2. Foreign Data Wrapper Callback Routines">Next</a></td></tr></table><hr /></div><div class="sect1" id="FDW-FUNCTIONS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">59.1. Foreign Data Wrapper Functions <a href="#FDW-FUNCTIONS" class="id_link">#</a></h2></div></div></div><p>3     The FDW author needs to implement a handler function, and optionally4     a validator function. Both functions must be written in a compiled5     language such as C, using the version-1 interface.6     For details on C language calling conventions and dynamic loading,7     see <a class="xref" href="xfunc-c.html" title="38.10. C-Language Functions">Section 38.10</a>.8    </p><p>9     The handler function simply returns a struct of function pointers to10     callback functions that will be called by the planner, executor, and11     various maintenance commands.12     Most of the effort in writing an FDW is in implementing these callback13     functions.14     The handler function must be registered with15     <span class="productname">PostgreSQL</span> as taking no arguments and16     returning the special pseudo-type <code class="type">fdw_handler</code>.  The17     callback functions are plain C functions and are not visible or18     callable at the SQL level.  The callback functions are described in19     <a class="xref" href="fdw-callbacks.html" title="59.2. Foreign Data Wrapper Callback Routines">Section 59.2</a>.20    </p><p>21     The validator function is responsible for validating options given in22     <code class="command">CREATE</code> and <code class="command">ALTER</code> commands for its23     foreign data wrapper, as well as foreign servers, user mappings, and24     foreign tables using the wrapper.25     The validator function must be registered as taking two arguments, a26     text array containing the options to be validated, and an OID27     representing the type of object the options are associated with. The28     latter corresponds to the OID of the system catalog the object29     would be stored in, one of:30     </p><div class="itemizedlist"><ul class="itemizedlist compact" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">AttributeRelationId</code></p></li><li class="listitem"><p><code class="literal">ForeignDataWrapperRelationId</code></p></li><li class="listitem"><p><code class="literal">ForeignServerRelationId</code></p></li><li class="listitem"><p><code class="literal">ForeignTableRelationId</code></p></li><li class="listitem"><p><code class="literal">UserMappingRelationId</code></p></li></ul></div><p>31     If no validator function is supplied, options are not checked at object32     creation time or object alteration time.33    </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="fdwhandler.html" title="Chapter 59. Writing a Foreign Data Wrapper">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="fdwhandler.html" title="Chapter 59. Writing a Foreign Data Wrapper">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="fdw-callbacks.html" title="59.2. Foreign Data Wrapper Callback Routines">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 59. Writing a Foreign Data Wrapper </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 59.2. Foreign Data Wrapper Callback Routines</td></tr></table></div></body></html>