v4-0002-POC-FK-and-CHECK-constraint-check.patch

From e159afbb82f8789e609b4b82013e5a8ddb761816 Mon Sep 17 00:00:00 2001
From: Amul Sul <amul.sul@enterprisedb.com>
Date: Fri, 17 Nov 2023 17:21:59 +0530
Subject: [PATCH v4 2/2] POC - FK and CHECK constraint check

---
 src/backend/commands/tablecmds.c | 163 ++++++++++++++++++++++++++++++-
 1 file changed, 162 insertions(+), 1 deletion(-)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 63debf1c376..0bb6143937b 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -4856,7 +4856,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 		case AT_SetExpression:	/* ALTER COLUMN SET EXPRESSION AS */
 			ATSimplePermissions(cmd->subtype, rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 			ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode, context);
-			pass = AT_PASS_MISC;
+			pass = AT_PASS_ALTER_TYPE;
 			break;
 		case AT_DropExpression: /* ALTER COLUMN DROP EXPRESSION */
 			ATSimplePermissions(cmd->subtype, rel, ATT_TABLE | ATT_FOREIGN_TABLE);
@@ -8345,6 +8345,12 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 	NewColumnValue *newval;
 	RawColumnDefault *rawEnt;
 
+	Relation	newrel;
+	Relation	depRel;
+	ScanKeyData key[3];
+	SysScanDesc scan;
+	HeapTuple	depTup;
+
 	tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);
 	if (!HeapTupleIsValid(tuple))
 		ereport(ERROR,
@@ -8415,6 +8421,161 @@ ATExecSetExpression(AlteredTableInfo *tab, Relation rel, const char *colName,
 	tab->newvals = lappend(tab->newvals, newval);
 	tab->rewrite |= AT_REWRITE_DEFAULT_VAL;
 
+	/*
+	 * TODO: needed?
+	 *
+	 * Clear all the missing values if we're rewriting the table, since this
+	 * renders them pointless.
+	 */
+	newrel = table_open(RelationGetRelid(rel), NoLock);
+	RelationClearMissing(newrel);
+	relation_close(newrel, NoLock);
+	/* make sure we don't conflict with later attribute modifications */
+	CommandCounterIncrement();
+
+	/*
+	 * Find everything that depends on the column (constraints, indexes, etc),
+	 * and record enough information to let us recreate the objects.
+	 *
+	 * The actual recreation does not happen here, but only after we have
+	 * performed all the individual ALTER TYPE operations.  We have to save
+	 * the info before executing ALTER TYPE, though, else the deparser will
+	 * get confused.
+	 */
+	depRel = table_open(DependRelationId, RowExclusiveLock);
+
+	ScanKeyInit(&key[0],
+				Anum_pg_depend_refclassid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationRelationId));
+	ScanKeyInit(&key[1],
+				Anum_pg_depend_refobjid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(RelationGetRelid(rel)));
+	ScanKeyInit(&key[2],
+				Anum_pg_depend_refobjsubid,
+				BTEqualStrategyNumber, F_INT4EQ,
+				Int32GetDatum((int32) attnum));
+
+	scan = systable_beginscan(depRel, DependReferenceIndexId, true,
+							  NULL, 3, key);
+
+	while (HeapTupleIsValid(depTup = systable_getnext(scan)))
+	{
+		Form_pg_depend foundDep = (Form_pg_depend) GETSTRUCT(depTup);
+		ObjectAddress foundObject;
+
+		foundObject.classId = foundDep->classid;
+		foundObject.objectId = foundDep->objid;
+		foundObject.objectSubId = foundDep->objsubid;
+
+		switch (getObjectClass(&foundObject))
+		{
+			case OCLASS_CLASS:
+				{
+					char		relKind = get_rel_relkind(foundObject.objectId);
+
+					if (relKind == RELKIND_INDEX ||
+						relKind == RELKIND_PARTITIONED_INDEX)
+					{
+						Assert(foundObject.objectSubId == 0);
+						RememberIndexForRebuilding(foundObject.objectId, tab);
+					}
+					else
+					{
+						/* Not expecting any other direct dependencies... */
+						elog(ERROR, "unexpected object depending on column: %s",
+							 getObjectDescription(&foundObject, false));
+					}
+					break;
+				}
+
+			case OCLASS_CONSTRAINT:
+				Assert(foundObject.objectSubId == 0);
+				RememberConstraintForRebuilding(foundObject.objectId, tab);
+				break;
+
+			/* TODO: need an explanation for the ignorance */
+			case OCLASS_REWRITE:
+			case OCLASS_TRIGGER:
+			case OCLASS_POLICY:
+				break;
+
+			case OCLASS_DEFAULT:
+				/* Ignore this since we adding a column default */
+				break;
+
+			case OCLASS_STATISTIC_EXT:
+
+				/*
+				 * Give the extended-stats machinery a chance to fix anything
+				 * that this column type change would break.
+				 */
+				RememberStatisticsForRebuilding(foundObject.objectId, tab);
+				break;
+
+			case OCLASS_PROC:
+			case OCLASS_TYPE:
+			case OCLASS_CAST:
+			case OCLASS_COLLATION:
+			case OCLASS_CONVERSION:
+			case OCLASS_LANGUAGE:
+			case OCLASS_LARGEOBJECT:
+			case OCLASS_OPERATOR:
+			case OCLASS_OPCLASS:
+			case OCLASS_OPFAMILY:
+			case OCLASS_AM:
+			case OCLASS_AMOP:
+			case OCLASS_AMPROC:
+			case OCLASS_SCHEMA:
+			case OCLASS_TSPARSER:
+			case OCLASS_TSDICT:
+			case OCLASS_TSTEMPLATE:
+			case OCLASS_TSCONFIG:
+			case OCLASS_ROLE:
+			case OCLASS_ROLE_MEMBERSHIP:
+			case OCLASS_DATABASE:
+			case OCLASS_TBLSPACE:
+			case OCLASS_FDW:
+			case OCLASS_FOREIGN_SERVER:
+			case OCLASS_USER_MAPPING:
+			case OCLASS_DEFACL:
+			case OCLASS_EXTENSION:
+			case OCLASS_EVENT_TRIGGER:
+			case OCLASS_PARAMETER_ACL:
+			case OCLASS_PUBLICATION:
+			case OCLASS_PUBLICATION_NAMESPACE:
+			case OCLASS_PUBLICATION_REL:
+			case OCLASS_SUBSCRIPTION:
+			case OCLASS_TRANSFORM:
+
+				/*
+				 * We don't expect any of these sorts of objects to depend on
+				 * a column.
+				 */
+				elog(ERROR, "unexpected object depending on column: %s",
+					 getObjectDescription(&foundObject, false));
+				break;
+
+				/*
+				 * There's intentionally no default: case here; we want the
+				 * compiler to warn if a new OCLASS hasn't been handled above.
+				 */
+		}
+	}
+
+	systable_endscan(scan);
+
+	table_close(depRel, RowExclusiveLock);
+
+	/*
+	 * Drop any pg_statistic entry for the column, no longer valid
+	 */
+	RemoveStatistics(RelationGetRelid(rel), attnum);
+
+	InvokeObjectPostAlterHook(RelationRelationId,
+							  RelationGetRelid(rel), attnum);
+
 	ObjectAddressSubSet(address, RelationRelationId,
 						RelationGetRelid(rel), attnum);
 	return address;
-- 
2.18.0