Support for weak binding views to allow dropping of underlying objects

Signed-off-by: Rahul Parande <[email protected]>

Author: Rahul Parande

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 +133,20 @@ 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)
+		{
+			Relation depRel = table_open(DependRelationId, AccessShareLock);
+			
+			if (!(*view_dependency_hook)(&address, depRel, NULL))
+			{
+				table_close(depRel, AccessShareLock);
+				continue;
+			}
+			
+			table_close(depRel, AccessShareLock);
+		}
 	}
 
 	/* 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 +1677,20 @@ 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)
+		{
+			Relation depRel = table_open(DependRelationId, AccessShareLock);
+			
+			if (!(*view_dependency_hook)(&obj, depRel, NULL))
+			{
+				table_close(depRel, AccessShareLock);
+				continue;
+			}
+			
+			table_close(depRel, AccessShareLock);
+		}
 	}
 
 	performMultipleDeletions(objects, drop->behavior, flags);

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

@@ -15822,52 +15822,6 @@ dumpTable(Archive *fout, const TableInfo *tbinfo)
 	free(namecopy);
 }
 
-/*
- * 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.
- *
- * This returns a new buffer which must be freed by the caller.
- */
-static PQExpBuffer
-createViewAsClause(Archive *fout, const TableInfo *tbinfo)
-{
-	PQExpBuffer query = createPQExpBuffer();
-	PQExpBuffer result = createPQExpBuffer();
-	PGresult   *res;
-	int			len;
-
-	/* Fetch the view definition */
-	appendPQExpBuffer(query,
-					  "SELECT pg_catalog.pg_get_viewdef('%u'::pg_catalog.oid) AS viewdef",
-					  tbinfo->dobj.catId.oid);
-
-	res = ExecuteSqlQuery(fout, query->data, PGRES_TUPLES_OK);
-
-	if (PQntuples(res) != 1)
-	{
-		if (PQntuples(res) < 1)
-			pg_fatal("query to obtain definition of view \"%s\" returned no data",
-					 tbinfo->dobj.name);
-		else
-			pg_fatal("query to obtain definition of view \"%s\" returned more than one definition",
-					 tbinfo->dobj.name);
-	}
-
-	len = PQgetlength(res, 0, 0);
-
-	if (len == 0)
-		pg_fatal("definition of view \"%s\" appears to be empty (length zero)",
-				 tbinfo->dobj.name);
-
-	/* Strip off the trailing semicolon so that other things may follow. */
-	Assert(PQgetvalue(res, 0, 0)[len - 1] == ';');
-	appendBinaryPQExpBuffer(result, PQgetvalue(res, 0, 0), len - 1);
-
-	PQclear(res);
-	destroyPQExpBuffer(query);
-
-	return result;
-}
 
 /*
  * Create a dummy AS clause for a view.  This is used when the real view
@@ -15913,6 +15867,66 @@ createDummyViewAsClause(Archive *fout, const TableInfo *tbinfo)
 	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.
+ *
+ * This returns a new buffer which must be freed by the caller.
+ */
+static PQExpBuffer
+createViewAsClause(Archive *fout, const TableInfo *tbinfo)
+{
+	PQExpBuffer query = createPQExpBuffer();
+	PQExpBuffer result = createPQExpBuffer();
+	PGresult   *res;
+	int			len;
+
+	/* Fetch the view definition */
+	appendPQExpBuffer(query,
+					  "SELECT pg_catalog.pg_get_viewdef('%u'::pg_catalog.oid) AS viewdef",
+					  tbinfo->dobj.catId.oid);
+
+	res = ExecuteSqlQuery(fout, query->data, PGRES_TUPLES_OK);
+
+	if (PQntuples(res) != 1)
+	{
+		if (PQntuples(res) < 1)
+			pg_fatal("query to obtain definition of view \"%s\" returned no data",
+					 tbinfo->dobj.name);
+		else
+			pg_fatal("query to obtain definition of view \"%s\" returned more than one definition",
+					 tbinfo->dobj.name);
+	}
+
+	len = PQgetlength(res, 0, 0);
+
+	if (len == 0)
+	{
+		/* 
+         * 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 */
+        PQExpBuffer 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] == ';');
+	appendBinaryPQExpBuffer(result, PQgetvalue(res, 0, 0), len - 1);
+
+	PQclear(res);
+	destroyPQExpBuffer(query);
+
+	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 */