diff options
Diffstat (limited to 'doc/src/sgml/fdwhandler.sgml')
| -rw-r--r-- | doc/src/sgml/fdwhandler.sgml | 65 |
1 files changed, 37 insertions, 28 deletions
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml index 635c9ec559a..0f2397df497 100644 --- a/doc/src/sgml/fdwhandler.sgml +++ b/doc/src/sgml/fdwhandler.sgml @@ -424,7 +424,8 @@ GetForeignUpperPaths(PlannerInfo *root, <para> <programlisting> void -AddForeignUpdateTargets(Query *parsetree, +AddForeignUpdateTargets(PlannerInfo *root, + Index rtindex, RangeTblEntry *target_rte, Relation target_relation); </programlisting> @@ -440,27 +441,31 @@ AddForeignUpdateTargets(Query *parsetree, </para> <para> - To do that, add <structname>TargetEntry</structname> items to - <literal>parsetree->targetList</literal>, containing expressions for the - extra values to be fetched. Each such entry must be marked - <structfield>resjunk</structfield> = <literal>true</literal>, and must have a distinct - <structfield>resname</structfield> that will identify it at execution time. - Avoid using names matching <literal>ctid<replaceable>N</replaceable></literal>, - <literal>wholerow</literal>, or - <literal>wholerow<replaceable>N</replaceable></literal>, as the core system can - generate junk columns of these names. - If the extra expressions are more complex than simple Vars, they - must be run through <function>eval_const_expressions</function> - before adding them to the target list. - </para> - - <para> - Although this function is called during planning, the - information provided is a bit different from that available to other - planning routines. - <literal>parsetree</literal> is the parse tree for the <command>UPDATE</command> or - <command>DELETE</command> command, while <literal>target_rte</literal> and - <literal>target_relation</literal> describe the target foreign table. + To do that, construct a <structname>Var</structname> representing + an extra value you need, and pass it + to <function>add_row_identity_var</function>, along with a name for + the junk column. (You can do this more than once if several columns + are needed.) You must choose a distinct junk column name for each + different <structname>Var</structname> you need, except + that <structname>Var</structname>s that are identical except for + the <structfield>varno</structfield> field can and should share a + column name. + The core system uses the junk column names + <literal>tableoid</literal> for a + table's <structfield>tableoid</structfield> column, + <literal>ctid</literal> + or <literal>ctid<replaceable>N</replaceable></literal> + for <structfield>ctid</structfield>, + <literal>wholerow</literal> + for a whole-row <structname>Var</structname> marked with + <structfield>vartype</structfield> = <type>RECORD</type>, + and <literal>wholerow<replaceable>N</replaceable></literal> + for a whole-row <structname>Var</structname> with + <structfield>vartype</structfield> equal to the table's declared rowtype. + Re-use these names when you can (the planner will combine duplicate + requests for identical junk columns). If you need another kind of + junk column besides these, it might be wise to choose a name prefixed + with your extension name, to avoid conflicts against other FDWs. </para> <para> @@ -495,8 +500,8 @@ PlanForeignModify(PlannerInfo *root, <literal>resultRelation</literal> identifies the target foreign table by its range table index. <literal>subplan_index</literal> identifies which target of the <structname>ModifyTable</structname> plan node this is, counting from zero; - use this if you want to index into <literal>plan->plans</literal> or other - substructure of the <literal>plan</literal> node. + use this if you want to index into per-target-relation substructures of the + <literal>plan</literal> node. </para> <para> @@ -703,10 +708,14 @@ ExecForeignUpdate(EState *estate, <literal>slot</literal> contains the new data for the tuple; it will match the row-type definition of the foreign table. <literal>planSlot</literal> contains the tuple that was generated by the - <structname>ModifyTable</structname> plan node's subplan; it differs from - <literal>slot</literal> in possibly containing additional <quote>junk</quote> - columns. In particular, any junk columns that were requested by - <function>AddForeignUpdateTargets</function> will be available from this slot. + <structname>ModifyTable</structname> plan node's subplan. Unlike + <literal>slot</literal>, this tuple contains only the new values for + columns changed by the query, so do not rely on attribute numbers of the + foreign table to index into <literal>planSlot</literal>. + Also, <literal>planSlot</literal> typically contains + additional <quote>junk</quote> columns. In particular, any junk columns + that were requested by <function>AddForeignUpdateTargets</function> will + be available from this slot. </para> <para> |