Support for weak binding views to allow dropping of underlying objects

src/backend/commands/dropcmds.c

@@ -19,9 +19,11 @@
 #include "catalog/dependency.h"
 #include "catalog/namespace.h"
 #include "catalog/objectaddress.h"
+#include "catalog/pg_depend_d.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_proc.h"
 #include "commands/defrem.h"
+#include "commands/tablecmds.h"
 #include "miscadmin.h"
 #include "parser/parser.h"
 #include "parser/parse_type.h"
@@ -131,6 +133,13 @@ RemoveObjects(DropStmt *stmt)
 			table_close(relation, NoLock);
 
 		add_exact_object_address(&address, objects);
+
+		/* Check for strong views and handle weak views */
+		if ((stmt->removeType == OBJECT_FUNCTION) && view_dependency_hook)
+		{			
+			if (!(*view_dependency_hook)(&address, NULL, NULL))
+				continue;
+		}
 	}
 
 	/* Here we really delete them. */

src/backend/commands/tablecmds.c

@@ -138,6 +138,7 @@ InvokePreDropColumnHook_type InvokePreDropColumnHook = NULL;
 check_extended_attoptions_hook_type check_extended_attoptions_hook = NULL;
 find_attr_by_name_from_column_def_list_hook_type
 	find_attr_by_name_from_column_def_list_hook = NULL;
+view_dependency_hook_type view_dependency_hook = NULL;
 
 /*
  * State information for ALTER TABLE
@@ -1676,6 +1677,13 @@ RemoveRelations(DropStmt *drop)
 		{
 			InvokeObjectDropHook(RelationRelationId,relOid,0);
 		}
+
+		/* Check for strong views and handle weak views */
+		if ((drop->removeType == OBJECT_TABLE || drop->removeType == OBJECT_VIEW) && view_dependency_hook)
+		{			
+			if (!(*view_dependency_hook)(&obj, NULL, NULL))
+				continue;
+		}
 	}
 
 	performMultipleDeletions(objects, drop->behavior, flags);

src/backend/commands/view.c

@@ -22,6 +22,7 @@
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "parser/analyze.h"
+#include "parser/parser.h"
 #include "parser/parse_relation.h"
 #include "rewrite/rewriteDefine.h"
 #include "rewrite/rewriteHandler.h"
@@ -36,6 +37,8 @@ static void checkViewColumns(TupleDesc newdesc, TupleDesc olddesc);
 
 inherit_view_constraints_from_table_hook_type inherit_view_constraints_from_table_hook = NULL;
 
+check_view_dependencies_hook_type check_view_dependencies_hook = NULL;
+
 /*---------------------------------------------------------------------
  * DefineVirtualRelation
  *
@@ -381,6 +384,9 @@ DefineView(ViewStmt *stmt, const char *queryString,
 
 	viewParse = parse_analyze_fixedparams(rawstmt, queryString, NULL, 0, NULL);
 
+	if (check_view_dependencies_hook)
+			(*check_view_dependencies_hook)(viewParse);
+
 	/*
 	 * The grammar should ensure that the result is a single SELECT Query.
 	 * However, it doesn't forbid SELECT INTO, so we have to check for that.

src/backend/rewrite/rewriteHandler.c

@@ -47,6 +47,7 @@
 #include "utils/rel.h"
 
 bbfViewHasInsteadofTrigger_hook_type bbfViewHasInsteadofTrigger_hook = NULL; /** BBF Hook to check Instead Of trigger on View */
+view_repair_hook_type view_repair_hook = NULL;
 
 /* We use a list of these to detect recursion in RewriteQuery */
 typedef struct rewrite_event
@@ -4403,7 +4404,6 @@ RewriteQuery(Query *parsetree, List *rewrite_events, int orig_rt_length)
 	return rewritten;
 }
 
-
 /*
  * QueryRewrite -
  *	  Primary entry point to the query rewriter.
@@ -4431,6 +4431,14 @@ QueryRewrite(Query *parsetree)
 	Assert(parsetree->canSetTag);
 
 	/*
+     * Step 0 (Babelfish extension)
+     *
+     * If this is a view with broken rules, try to repair it
+     * using the definition from babelfish_view_def
+     */
+	if (view_repair_hook)
+		(*view_repair_hook)(parsetree);
+	/*
 	 * Step 1
 	 *
 	 * Apply all non-SELECT rules possibly getting 0 or many queries

src/bin/pg_dump/pg_dump.c

@@ -15822,6 +15822,50 @@ dumpTable(Archive *fout, const TableInfo *tbinfo)
 	free(namecopy);
 }
 
+/*
+ * Create a dummy AS clause for a view.  This is used when the real view
+ * definition has to be postponed because of circular dependencies.
+ * We must duplicate the view's external properties -- column names and types
+ * (including collation) -- so that it works for subsequent references.
+ *
+ * This returns a new buffer which must be freed by the caller.
+ */
+static PQExpBuffer
+createDummyViewAsClause(Archive *fout, const TableInfo *tbinfo)
+{
+	PQExpBuffer result = createPQExpBuffer();
+	int			j;
+
+	appendPQExpBufferStr(result, "SELECT");
+
+	for (j = 0; j < tbinfo->numatts; j++)
+	{
+		if (j > 0)
+			appendPQExpBufferChar(result, ',');
+		appendPQExpBufferStr(result, "\n    ");
+
+		appendPQExpBuffer(result, "NULL::%s", tbinfo->atttypnames[j]);
+
+		/*
+		 * Must add collation if not default for the type, because CREATE OR
+		 * REPLACE VIEW won't change it
+		 */
+		if (OidIsValid(tbinfo->attcollation[j]))
+		{
+			CollInfo   *coll;
+
+			coll = findCollationByOid(tbinfo->attcollation[j]);
+			if (coll)
+				appendPQExpBuffer(result, " COLLATE %s",
+								  fmtQualifiedDumpable(coll));
+		}
+
+		appendPQExpBuffer(result, " AS %s", fmtId(tbinfo->attnames[j]));
+	}
+
+	return result;
+}
+
 /*
  * Create the AS clause for a view or materialized view. The semicolon is
  * stripped because a materialized view must add a WITH NO DATA clause.
@@ -15833,6 +15877,7 @@ createViewAsClause(Archive *fout, const TableInfo *tbinfo)
 {
 	PQExpBuffer query = createPQExpBuffer();
 	PQExpBuffer result = createPQExpBuffer();
+	PQExpBuffer dummyResult = createPQExpBuffer();
 	PGresult   *res;
 	int			len;
 
@@ -15856,8 +15901,21 @@ createViewAsClause(Archive *fout, const TableInfo *tbinfo)
 	len = PQgetlength(res, 0, 0);
 
 	if (len == 0)
-		pg_fatal("definition of view \"%s\" appears to be empty (length zero)",
-				 tbinfo->dobj.name);
+	{
+		/* 
+		 * Handle broken views (with empty definitions)
+		 * Instead of failing, create a dummy SELECT that preserves the structure
+		 */
+		PQclear(res);
+		destroyPQExpBuffer(query);
+
+		/* Use createDummyViewAsClause to generate a compatible structure */
+		dummyResult = createDummyViewAsClause(fout, tbinfo);
+		appendPQExpBuffer(result, "%s", dummyResult->data);
+		destroyPQExpBuffer(dummyResult);
+
+		return result;
+	}
 
 	/* Strip off the trailing semicolon so that other things may follow. */
 	Assert(PQgetvalue(res, 0, 0)[len - 1] == ';');
@@ -15869,50 +15927,6 @@ createViewAsClause(Archive *fout, const TableInfo *tbinfo)
 	return result;
 }
 
-/*
- * Create a dummy AS clause for a view.  This is used when the real view
- * definition has to be postponed because of circular dependencies.
- * We must duplicate the view's external properties -- column names and types
- * (including collation) -- so that it works for subsequent references.
- *
- * This returns a new buffer which must be freed by the caller.
- */
-static PQExpBuffer
-createDummyViewAsClause(Archive *fout, const TableInfo *tbinfo)
-{
-	PQExpBuffer result = createPQExpBuffer();
-	int			j;
-
-	appendPQExpBufferStr(result, "SELECT");
-
-	for (j = 0; j < tbinfo->numatts; j++)
-	{
-		if (j > 0)
-			appendPQExpBufferChar(result, ',');
-		appendPQExpBufferStr(result, "\n    ");
-
-		appendPQExpBuffer(result, "NULL::%s", tbinfo->atttypnames[j]);
-
-		/*
-		 * Must add collation if not default for the type, because CREATE OR
-		 * REPLACE VIEW won't change it
-		 */
-		if (OidIsValid(tbinfo->attcollation[j]))
-		{
-			CollInfo   *coll;
-
-			coll = findCollationByOid(tbinfo->attcollation[j]);
-			if (coll)
-				appendPQExpBuffer(result, " COLLATE %s",
-								  fmtQualifiedDumpable(coll));
-		}
-
-		appendPQExpBuffer(result, " AS %s", fmtId(tbinfo->attnames[j]));
-	}
-
-	return result;
-}
-
 /*
  * dumpTableSchema
  *	  write the declaration (not data) of one user-defined table or view

src/include/commands/tablecmds.h

@@ -122,4 +122,8 @@ typedef int (*find_attr_by_name_from_column_def_list_hook_type) (
 extern PGDLLEXPORT find_attr_by_name_from_column_def_list_hook_type
 	find_attr_by_name_from_column_def_list_hook;
 
+/* Hook for handling view dependencies during table drops */
+typedef bool (*view_dependency_hook_type) (const ObjectAddress *droppedObject, Relation depRel, ViewStmt *viewstmt);
+extern PGDLLIMPORT view_dependency_hook_type view_dependency_hook;
+
 #endif							/* TABLECMDS_H */

src/include/commands/view.h

@@ -27,4 +27,7 @@ extern PGDLLEXPORT store_view_definition_hook_type	store_view_definition_hook;
 
 typedef void (*inherit_view_constraints_from_table_hook_type) (ColumnDef  *col, Oid tableOid, AttrNumber colId);
 extern PGDLLEXPORT inherit_view_constraints_from_table_hook_type inherit_view_constraints_from_table_hook;
+
+typedef bool (*check_view_dependencies_hook_type) (Query *viewParse);
+extern check_view_dependencies_hook_type check_view_dependencies_hook;
 #endif							/* VIEW_H */

src/include/rewrite/rewriteHandler.h

@@ -38,4 +38,8 @@ extern void error_view_not_updatable(Relation view,
 									 List *mergeActionList,
 									 const char *detail);
 
+/* View repair hook */
+typedef bool (*view_repair_hook_type) (Query *parsetree);
+extern PGDLLEXPORT view_repair_hook_type view_repair_hook;									 
+
 #endif							/* REWRITEHANDLER_H */