From fba6464f1555ec05029a58e2bf378ef83ce73172 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Sun, 1 Jul 2018 23:26:10 +0900
Subject: [PATCH 1/3] Extend lookup routines for FDW and foreign server with
 NULL handling

The cache lookup routines for foreign-data wrappers and foreign servers
are extended with an extra argument able to control if an error or a
NULL object is returned to the caller in the event of an undefined
object. This is added in a set of new routines to not impact
unnecessrily any FPW plugins.
---
 doc/src/sgml/fdwhandler.sgml  | 30 +++++++++++++++++++++++++++++
 src/backend/foreign/foreign.c | 36 +++++++++++++++++++++++++++++++++--
 src/include/foreign/foreign.h |  4 ++++
 3 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 4ce88dd77c..a68e264261 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -1408,6 +1408,21 @@ ReparameterizeForeignPathByChild(PlannerInfo *root, List *fdw_private,
     <para>
 <programlisting>
 ForeignDataWrapper *
+GetForeignDataWrapperExtended(Oid fdwid, bool missing_ok);
+</programlisting>
+
+     This function returns a <structname>ForeignDataWrapper</structname>
+     object for the foreign-data wrapper with the given OID.  A
+     <structname>ForeignDataWrapper</structname> object contains properties
+     of the FDW (see <filename>foreign/foreign.h</filename> for details).
+     If <literal>missing_ok</literal> is true, a <literal>NULL</literal>
+     result is returned to the caller instead of an error for an undefined
+     FDW.
+    </para>
+
+    <para>
+<programlisting>
+ForeignDataWrapper *
 GetForeignDataWrapper(Oid fdwid);
 </programlisting>
 
@@ -1420,6 +1435,21 @@ GetForeignDataWrapper(Oid fdwid);
     <para>
 <programlisting>
 ForeignServer *
+GetForeignServerExtended(Oid serverid, bool missing_ok);
+</programlisting>
+
+     This function returns a <structname>ForeignServer</structname> object
+     for the foreign server with the given OID.  A
+     <structname>ForeignServer</structname> object contains properties
+     of the server (see <filename>foreign/foreign.h</filename> for details).
+     If <literal>missing_ok</literal> is true, a <literal>NULL</literal>
+     result is returned to the caller instead of an error for an undefined
+     foreign server.
+    </para>
+
+    <para>
+<programlisting>
+ForeignServer *
 GetForeignServer(Oid serverid);
 </programlisting>
 
diff --git a/src/backend/foreign/foreign.c b/src/backend/foreign/foreign.c
index eac78a5d31..01b5175e71 100644
--- a/src/backend/foreign/foreign.c
+++ b/src/backend/foreign/foreign.c
@@ -33,6 +33,18 @@
  */
 ForeignDataWrapper *
 GetForeignDataWrapper(Oid fdwid)
+{
+	return GetForeignDataWrapperExtended(fdwid, false);
+}
+
+
+/*
+ * GetForeignDataWrapperExtended -	look up the foreign-data wrapper
+ * by OID. If missing_ok is true, return NULL if the object cannot be
+ * found instead of raising an error.
+ */
+ForeignDataWrapper *
+GetForeignDataWrapperExtended(Oid fdwid, bool missing_ok)
 {
 	Form_pg_foreign_data_wrapper fdwform;
 	ForeignDataWrapper *fdw;
@@ -43,7 +55,11 @@ GetForeignDataWrapper(Oid fdwid)
 	tp = SearchSysCache1(FOREIGNDATAWRAPPEROID, ObjectIdGetDatum(fdwid));
 
 	if (!HeapTupleIsValid(tp))
-		elog(ERROR, "cache lookup failed for foreign-data wrapper %u", fdwid);
+	{
+		if (!missing_ok)
+			elog(ERROR, "cache lookup failed for foreign-data wrapper %u", fdwid);
+		return NULL;
+	}
 
 	fdwform = (Form_pg_foreign_data_wrapper) GETSTRUCT(tp);
 
@@ -91,6 +107,18 @@ GetForeignDataWrapperByName(const char *fdwname, bool missing_ok)
  */
 ForeignServer *
 GetForeignServer(Oid serverid)
+{
+	return GetForeignServerExtended(serverid, false);
+}
+
+
+/*
+ * GetForeignServerExtended - look up the foreign server definition. If
+ * missing_ok is true, return NULL if the object cannot be found instead
+ * of raising an error.
+ */
+ForeignServer *
+GetForeignServerExtended(Oid serverid, bool missing_ok)
 {
 	Form_pg_foreign_server serverform;
 	ForeignServer *server;
@@ -101,7 +129,11 @@ GetForeignServer(Oid serverid)
 	tp = SearchSysCache1(FOREIGNSERVEROID, ObjectIdGetDatum(serverid));
 
 	if (!HeapTupleIsValid(tp))
-		elog(ERROR, "cache lookup failed for foreign server %u", serverid);
+	{
+		if (!missing_ok)
+			elog(ERROR, "cache lookup failed for foreign server %u", serverid);
+		return NULL;
+	}
 
 	serverform = (Form_pg_foreign_server) GETSTRUCT(tp);
 
diff --git a/src/include/foreign/foreign.h b/src/include/foreign/foreign.h
index 3ca12e64d2..5cc89e967c 100644
--- a/src/include/foreign/foreign.h
+++ b/src/include/foreign/foreign.h
@@ -70,9 +70,13 @@ typedef struct ForeignTable
 
 
 extern ForeignServer *GetForeignServer(Oid serverid);
+extern ForeignServer *GetForeignServerExtended(Oid serverid,
+							bool missing_ok);
 extern ForeignServer *GetForeignServerByName(const char *name, bool missing_ok);
 extern UserMapping *GetUserMapping(Oid userid, Oid serverid);
 extern ForeignDataWrapper *GetForeignDataWrapper(Oid fdwid);
+extern ForeignDataWrapper *GetForeignDataWrapperExtended(Oid fdwid,
+							bool missing_ok);
 extern ForeignDataWrapper *GetForeignDataWrapperByName(const char *name,
 							bool missing_ok);
 extern ForeignTable *GetForeignTable(Oid relid);
-- 
2.19.0