Improve UPDATE/DELETE WHERE CURRENT OF so that they can be used from plpgsql

with a plpgsql-defined cursor.  The underlying mechanism for this is that the
main SQL engine will now take "WHERE CURRENT OF $n" where $n is a refcursor
parameter.  Not sure if we should document that fact or consider it an
implementation detail.  Per discussion with Pavel Stehule.

Author: tglsfdc

doc/src/sgml/plpgsql.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.111 2007/06/11 15:08:32 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.112 2007/06/11 22:22:40 tgl Exp $ -->
 
 <chapter id="plpgsql"> 
   <title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@@ -2614,6 +2614,31 @@ MOVE <optional> <replaceable>direction</replaceable> { FROM | IN } </optional> <
 MOVE curs1;
 MOVE LAST FROM curs3;
 MOVE RELATIVE -2 FROM curs4;
+</programlisting>
+       </para>
+     </sect3>
+
+    <sect3>
+     <title><literal>UPDATE/DELETE WHERE CURRENT OF</></title>
+
+<synopsis>
+UPDATE <replaceable>table</replaceable> SET ... WHERE CURRENT OF <replaceable>cursor</replaceable>;
+DELETE FROM <replaceable>table</replaceable> WHERE CURRENT OF <replaceable>cursor</replaceable>;
+</synopsis>
+
+       <para>
+        When a cursor is positioned on a table row, that row can be updated
+        or deleted using the cursor to identify the row.  Note that this
+        only works for simple (non-join, non-grouping) cursor queries.
+        For additional information see the
+        <xref linkend="sql-declare" endterm="sql-declare-title">
+        reference page.
+       </para>
+
+       <para>
+        An example:
+<programlisting>
+UPDATE foo SET dataval = myval WHERE CURRENT OF curs1;
 </programlisting>
        </para>
      </sect3>

src/backend/executor/execCurrent.c

@@ -6,41 +6,55 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$PostgreSQL: pgsql/src/backend/executor/execCurrent.c,v 1.1 2007/06/11 01:16:22 tgl Exp $
+ *	$PostgreSQL: pgsql/src/backend/executor/execCurrent.c,v 1.2 2007/06/11 22:22:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
+#include "catalog/pg_type.h"
 #include "executor/executor.h"
+#include "utils/builtins.h"
 #include "utils/lsyscache.h"
 #include "utils/portal.h"
 
 
+static char *fetch_param_value(ExprContext *econtext, int paramId);
 static ScanState *search_plan_tree(PlanState *node, Oid table_oid);
 
 
 /*
  * execCurrentOf
  *
- * Given the name of a cursor and the OID of a table, determine which row
- * of the table is currently being scanned by the cursor, and return its
- * TID into *current_tid.
+ * Given a CURRENT OF expression and the OID of a table, determine which row
+ * of the table is currently being scanned by the cursor named by CURRENT OF,
+ * and return the row's TID into *current_tid.
  *
  * Returns TRUE if a row was identified.  Returns FALSE if the cursor is valid
  * for the table but is not currently scanning a row of the table (this is a
  * legal situation in inheritance cases).  Raises error if cursor is not a
  * valid updatable scan of the specified table.
  */
 bool
-execCurrentOf(char *cursor_name, Oid table_oid,
+execCurrentOf(CurrentOfExpr *cexpr,
+			  ExprContext *econtext,
+			  Oid table_oid,
 			  ItemPointer current_tid)
 {
+	char	   *cursor_name;
 	char	   *table_name;
 	Portal		portal;
 	QueryDesc *queryDesc;
 	ScanState  *scanstate;
-	HeapTuple tup;
+	bool	lisnull;
+	Oid		tuple_tableoid;
+	ItemPointer tuple_tid;
+
+	/* Get the cursor name --- may have to look up a parameter reference */
+	if (cexpr->cursor_name)
+		cursor_name = cexpr->cursor_name;
+	else
+		cursor_name = fetch_param_value(econtext, cexpr->cursor_param);
 
 	/* Fetch table name for possible use in error messages */
 	table_name = get_rel_name(table_oid);
@@ -100,16 +114,54 @@ execCurrentOf(char *cursor_name, Oid table_oid,
 	if (TupIsNull(scanstate->ss_ScanTupleSlot))
 		return false;
 
-	tup = scanstate->ss_ScanTupleSlot->tts_tuple;
-	if (tup == NULL)
-		elog(ERROR, "CURRENT OF applied to non-materialized tuple");
-	Assert(tup->t_tableOid == table_oid);
+	/* Use slot_getattr to catch any possible mistakes */
+	tuple_tableoid = DatumGetObjectId(slot_getattr(scanstate->ss_ScanTupleSlot,
+												   TableOidAttributeNumber,
+												   &lisnull));
+	Assert(!lisnull);
+	tuple_tid = (ItemPointer)
+		DatumGetPointer(slot_getattr(scanstate->ss_ScanTupleSlot,
+									 SelfItemPointerAttributeNumber,
+									 &lisnull));
+	Assert(!lisnull);
+
+	Assert(tuple_tableoid == table_oid);
 
-	*current_tid = tup->t_self;
+	*current_tid = *tuple_tid;
 
 	return true;
 }
 
+/*
+ * fetch_param_value
+ *
+ * Fetch the string value of a param, verifying it is of type REFCURSOR.
+ */
+static char *
+fetch_param_value(ExprContext *econtext, int paramId)
+{
+	ParamListInfo paramInfo = econtext->ecxt_param_list_info;
+
+	if (paramInfo &&
+		paramId > 0 && paramId <= paramInfo->numParams)
+	{
+		ParamExternData *prm = &paramInfo->params[paramId - 1];
+
+		if (OidIsValid(prm->ptype) && !prm->isnull)
+		{
+			Assert(prm->ptype == REFCURSOROID);
+			/* We know that refcursor uses text's I/O routines */
+			return DatumGetCString(DirectFunctionCall1(textout,
+													   prm->value));
+		}
+	}
+
+	ereport(ERROR,
+			(errcode(ERRCODE_UNDEFINED_OBJECT),
+			 errmsg("no value found for parameter %d", paramId)));
+	return NULL;
+}
+
 /*
  * search_plan_tree
  *

src/backend/executor/execQual.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.219 2007/06/11 01:16:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.220 2007/06/11 22:22:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3632,8 +3632,10 @@ ExecEvalCurrentOfExpr(ExprState *exprstate, ExprContext *econtext,
 					  bool *isNull, ExprDoneCond *isDone)
 {
 	CurrentOfExpr *cexpr = (CurrentOfExpr *) exprstate->expr;
-	bool result;
-	HeapTuple tup;
+	bool	result;
+	bool	lisnull;
+	Oid		tableoid;
+	ItemPointer tuple_tid;
 	ItemPointerData cursor_tid;
 
 	if (isDone)
@@ -3643,12 +3645,19 @@ ExecEvalCurrentOfExpr(ExprState *exprstate, ExprContext *econtext,
 	Assert(cexpr->cvarno != INNER);
 	Assert(cexpr->cvarno != OUTER);
 	Assert(!TupIsNull(econtext->ecxt_scantuple));
-	tup = econtext->ecxt_scantuple->tts_tuple;
-	if (tup == NULL)
-		elog(ERROR, "CURRENT OF applied to non-materialized tuple");
-
-	if (execCurrentOf(cexpr->cursor_name, tup->t_tableOid, &cursor_tid))
-		result = ItemPointerEquals(&cursor_tid, &(tup->t_self));
+	/* Use slot_getattr to catch any possible mistakes */
+	tableoid = DatumGetObjectId(slot_getattr(econtext->ecxt_scantuple,
+											 TableOidAttributeNumber,
+											 &lisnull));
+	Assert(!lisnull);
+	tuple_tid = (ItemPointer)
+		DatumGetPointer(slot_getattr(econtext->ecxt_scantuple,
+									 SelfItemPointerAttributeNumber,
+									 &lisnull));
+	Assert(!lisnull);
+
+	if (execCurrentOf(cexpr, econtext, tableoid, &cursor_tid))
+		result = ItemPointerEquals(&cursor_tid, tuple_tid);
 	else
 		result = false;
 

src/backend/executor/nodeTidscan.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeTidscan.c,v 1.54 2007/06/11 01:16:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeTidscan.c,v 1.55 2007/06/11 22:22:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -153,7 +153,7 @@ TidListCreate(TidScanState *tidstate)
 			CurrentOfExpr *cexpr = (CurrentOfExpr *) expr;
 			ItemPointerData cursor_tid;
 
-			if (execCurrentOf(cexpr->cursor_name,
+			if (execCurrentOf(cexpr, econtext,
 						  RelationGetRelid(tidstate->ss.ss_currentRelation),
 							  &cursor_tid))
 			{

src/backend/nodes/copyfuncs.c

@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.378 2007/06/11 01:16:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.379 2007/06/11 22:22:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1309,6 +1309,7 @@ _copyCurrentOfExpr(CurrentOfExpr *from)
 
 	COPY_SCALAR_FIELD(cvarno);
 	COPY_STRING_FIELD(cursor_name);
+	COPY_SCALAR_FIELD(cursor_param);
 
 	return newnode;
 }

src/backend/nodes/equalfuncs.c

@@ -18,7 +18,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.309 2007/06/11 01:16:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.310 2007/06/11 22:22:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -603,6 +603,7 @@ _equalCurrentOfExpr(CurrentOfExpr *a, CurrentOfExpr *b)
 {
 	COMPARE_SCALAR_FIELD(cvarno);
 	COMPARE_STRING_FIELD(cursor_name);
+	COMPARE_SCALAR_FIELD(cursor_param);
 
 	return true;
 }

src/backend/nodes/outfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.310 2007/06/11 01:16:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.311 2007/06/11 22:22:40 tgl Exp $
  *
  * NOTES
  *	  Every node type that can appear in stored rules' parsetrees *must*
@@ -1065,6 +1065,7 @@ _outCurrentOfExpr(StringInfo str, CurrentOfExpr *node)
 
 	WRITE_UINT_FIELD(cvarno);
 	WRITE_STRING_FIELD(cursor_name);
+	WRITE_INT_FIELD(cursor_param);
 }
 
 static void

src/backend/nodes/readfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.208 2007/06/11 01:16:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.209 2007/06/11 22:22:41 tgl Exp $
  *
  * NOTES
  *	  Path and Plan nodes do not have any readfuncs support, because we
@@ -883,6 +883,7 @@ _readCurrentOfExpr(void)
 
 	READ_UINT_FIELD(cvarno);
 	READ_STRING_FIELD(cursor_name);
+	READ_INT_FIELD(cursor_param);
 
 	READ_DONE();
 }

src/backend/parser/gram.y

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.592 2007/06/11 01:16:25 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.593 2007/06/11 22:22:41 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -6568,7 +6568,17 @@ where_or_current_clause:
 			| WHERE CURRENT_P OF name
 				{
 					CurrentOfExpr *n = makeNode(CurrentOfExpr);
+					/* cvarno is filled in by parse analysis */
 					n->cursor_name = $4;
+					n->cursor_param = 0;
+					$$ = (Node *) n;
+				}
+			| WHERE CURRENT_P OF PARAM
+				{
+					CurrentOfExpr *n = makeNode(CurrentOfExpr);
+					/* cvarno is filled in by parse analysis */
+					n->cursor_name = NULL;
+					n->cursor_param = $4;
 					$$ = (Node *) n;
 				}
 			| /*EMPTY*/								{ $$ = NULL; }