I think that this function is needed so that PL/<lang> authors like myself have a way to investigate the semantics of a prepared query. For me this is essential since I want to prevent that savepoint related statements are executed using normal SQL so that I can enforce the use of the methods stipulated by the connection interface.
I forsee that this might be of interest for other PL/<lang> authors as well. With this patch in place, it will be possible to do things like this (returning false is rejecting in this case since false terminates the iteration):
static bool rejectTransactionCommand(Query* query, void* clientData)
{
return !(query->commandType == CMD_UTILITY &&
IsA(query->utilityStmt, TransactionStmt));
}and then use that like:
result = !SPI_iterate_query_roots(ePlan, rejectTransactionCommand, NULL);
The patch has no side effects since it's a pure addon.
Kind regards, Thomas Hallgren
Index: doc/src/sgml/spi.sgml
===================================================================
RCS file: /projects/cvsroot/pgsql/doc/src/sgml/spi.sgml,v
retrieving revision 1.35
diff -u -r1.35 spi.sgml
--- doc/src/sgml/spi.sgml 13 Sep 2004 20:05:25 -0000 1.35
+++ doc/src/sgml/spi.sgml 1 Dec 2004 19:05:28 -0000
@@ -1305,6 +1305,82 @@
<!-- *********************************************** -->
+<refentry id="spi-spi-iterate-query-roots">
+ <refmeta>
+ <refentrytitle>SPI_iterate_query_roots</refentrytitle>
+ </refmeta>
+
+ <refnamediv>
+ <refname>SPI_iterate_query_roots</refname>
+ <refpurpose>investigate the semantics of a query</refpurpose>
+ </refnamediv>
+
+ <indexterm><primary>SPI_iterate_query_roots</primary></indexterm>
+
+ <refsynopsisdiv>
+<synopsis>
+bool SPI_iterate_query_roots(void * <parameter>plan</parameter>, QueryVisitor
<parameter>callback</parameter>, void * <parameter>clientData</parameter>)
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>
+ The <function>SPI_iterate_query_roots</function> will invoke the
+ <symbol>queryVisitor</symbol> callback once for each top level
+ <symbol>Query</symbol> found in the supplied execution plan.
+ The iteration is cancelled when a callback returns <symbol>false</symbol>.
+ If no callback returns <symbol>false</symbol>, or if the plan is
+ <symbol>NULL</symbol>, the function returns <symbol>true</symbol>.
+ </para>
+ </refsect1>
+
+ <refsect1>
+ <title>Arguments</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><literal>void * <parameter>plan</parameter></literal></term>
+ <listitem>
+ <para>
+ execution plan (returned by <function>SPI_prepare</function>)
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>QueryVisitor
<parameter>callback</parameter></literal></term>
+ <listitem>
+ <para>
+ the callback to invoke for each query found
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>void * <parameter>clientData</parameter></literal></term>
+ <listitem>
+ <para>
+ user defined data that will be passed on to the callback
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+ <para>
+ <symbol>true</symbol> when all callbacks returned <symbol>true</symbol> or
+ <symbol>false</symbol> when a callback returned <symbol>false</symbol> and
+ thus terminated the iteration.
+ </para>
+ </refsect1>
+</refentry>
+
+<!-- *********************************************** -->
+
<refentry id="spi-spi-cursor-find">
<refmeta>
<refentrytitle>SPI_cursor_find</refentrytitle>
Index: src/backend/executor/spi.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/executor/spi.c,v
retrieving revision 1.132
diff -u -r1.132 spi.c
--- src/backend/executor/spi.c 16 Nov 2004 18:10:13 -0000 1.132
+++ src/backend/executor/spi.c 1 Dec 2004 19:05:29 -0000
@@ -1064,6 +1064,42 @@
return false;
}
+/**
+ * Invokes the queryVisitor callback for each top level Query found in an
+ * execution plan. The iteration is cancelled when a callback returns
+ * false. If no callbacks returns false, or if the plan is NULL, this
+ * function returns true.
+ *
+ * Arguments:
+ * plan An ExecutionPlan created by SPI_prepare
+ * queryVisitor The callback function
+ * clientData User defined data that will be passed on to the callback
+ * Returns: true if the plan is NULL or if all callback invocation returns true
+ */
+bool
+SPI_iterate_query_roots(void *plan, QueryVisitor queryVisitor, void
*clientData)
+{
+ _SPI_plan *spiplan = (_SPI_plan *) plan;
+
+ if (spiplan != NULL)
+ {
+ ListCell *query_list_list_item;
+ List *query_list_list = spiplan->qtlist;
+ foreach(query_list_list_item, query_list_list)
+ {
+ List *query_list = lfirst(query_list_list_item);
+ ListCell *query_list_item;
+
+ foreach(query_list_item, query_list)
+ {
+ if(!queryVisitor((Query
*)lfirst(query_list_item), clientData))
+ return false;
+ }
+ }
+ }
+ return true;
+}
+
/*
* SPI_result_code_string --- convert any SPI return code to a string
*
Index: src/include/executor/spi.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/include/executor/spi.h,v
retrieving revision 1.50
diff -u -r1.50 spi.h
--- src/include/executor/spi.h 16 Nov 2004 18:10:13 -0000 1.50
+++ src/include/executor/spi.h 1 Dec 2004 19:05:30 -0000
@@ -119,6 +119,9 @@
extern void SPI_freetuple(HeapTuple pointer);
extern void SPI_freetuptable(SPITupleTable *tuptable);
+typedef bool (*QueryVisitor)(Query* query, void *clientData);
+extern bool SPI_iterate_query_roots(void *plan, QueryVisitor queryVisitor,
void* clientData);
+
extern Portal SPI_cursor_open(const char *name, void *plan,
Datum *Values, const char *Nulls, bool
read_only);
extern Portal SPI_cursor_find(const char *name);
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