From beaf5ae623f9dd323da095fb65c74768ebc8afc5 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 24 Jan 2005 23:21:57 +0000
Subject: [PATCH] Fix ALTER TABLE ADD COLUMN so that constraints of domain
 types are enforced properly when there is no explicit default value for the
 new column.  Per report from Craig Perras.

---
 src/backend/commands/tablecmds.c | 35 ++++++++++++++++++++++++++++++++---
 src/backend/commands/typecmds.c  | 21 ++++++++++++---------
 2 files changed, 44 insertions(+), 12 deletions(-)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index b788db35cb..89dd8dffae 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.142 2005/01/10 20:02:20 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.143 2005/01/24 23:21:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -35,6 +35,7 @@
 #include "commands/tablecmds.h"
 #include "commands/tablespace.h"
 #include "commands/trigger.h"
+#include "commands/typecmds.h"
 #include "executor/executor.h"
 #include "lib/stringinfo.h"
 #include "miscadmin.h"
@@ -2853,6 +2854,7 @@ ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
 	int			minattnum,
 				maxatts;
 	HeapTuple	typeTuple;
+	Oid			typeOid;
 	Form_pg_type tform;
 	Expr	   *defval;
 
@@ -2930,9 +2932,10 @@ ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
 
 	typeTuple = typenameType(colDef->typename);
 	tform = (Form_pg_type) GETSTRUCT(typeTuple);
+	typeOid = HeapTupleGetOid(typeTuple);
 
 	/* make sure datatype is legal for a column */
-	CheckAttributeType(colDef->colname, HeapTupleGetOid(typeTuple));
+	CheckAttributeType(colDef->colname, typeOid);
 
 	attributeTuple = heap_addheader(Natts_pg_attribute,
 									false,
@@ -2943,7 +2946,7 @@ ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
 
 	attribute->attrelid = myrelid;
 	namestrcpy(&(attribute->attname), colDef->colname);
-	attribute->atttypid = HeapTupleGetOid(typeTuple);
+	attribute->atttypid = typeOid;
 	attribute->attstattarget = -1;
 	attribute->attlen = tform->typlen;
 	attribute->attcacheoff = -1;
@@ -3015,11 +3018,37 @@ ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
 	 * and return NULL if so, so without any modification of the tuple
 	 * data we will get the effect of NULL values in the new column.
 	 *
+	 * An exception occurs when the new column is of a domain type: the
+	 * domain might have a NOT NULL constraint, or a check constraint that
+	 * indirectly rejects nulls.  If there are any domain constraints then
+	 * we construct an explicit NULL default value that will be passed through
+	 * CoerceToDomain processing.  (This is a tad inefficient, since it
+	 * causes rewriting the table which we really don't have to do, but
+	 * the present design of domain processing doesn't offer any simple way
+	 * of checking the constraints more directly.)
+	 *
 	 * Note: we use build_column_default, and not just the cooked default
 	 * returned by AddRelationRawConstraints, so that the right thing
 	 * happens when a datatype's default applies.
 	 */
 	defval = (Expr *) build_column_default(rel, attribute->attnum);
+
+	if (!defval && GetDomainConstraints(typeOid) != NIL)
+	{
+		Oid		basetype = getBaseType(typeOid);
+
+		defval = (Expr *) makeNullConst(basetype);
+		defval = (Expr *) coerce_to_target_type(NULL,
+												(Node *) defval,
+												basetype,
+												typeOid,
+												colDef->typename->typmod,
+												COERCION_ASSIGNMENT,
+												COERCE_IMPLICIT_CAST);
+		if (defval == NULL)		/* should not happen */
+			elog(ERROR, "failed to coerce base type to domain");
+	}
+
 	if (defval)
 	{
 		NewColumnValue *newval;
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index efeb3f3bab..d9fffbec27 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/typecmds.c,v 1.65 2004/12/31 21:59:42 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/typecmds.c,v 1.66 2005/01/24 23:21:57 tgl Exp $
  *
  * DESCRIPTION
  *	  The "DefineFoo" routines take the parse tree and pick out the
@@ -1929,6 +1929,9 @@ domainAddConstraint(Oid domainOid, Oid domainNamespace, Oid baseTypeOid,
  * This is called by the executor during plan startup for a CoerceToDomain
  * expression node.  The given constraints will be checked for each value
  * passed through the node.
+ *
+ * We allow this to be called for non-domain types, in which case the result
+ * is always NIL.
  */
 List *
 GetDomainConstraints(Oid typeOid)
@@ -1954,6 +1957,13 @@ GetDomainConstraints(Oid typeOid)
 			elog(ERROR, "cache lookup failed for type %u", typeOid);
 		typTup = (Form_pg_type) GETSTRUCT(tup);
 
+		if (typTup->typtype != 'd')
+		{
+			/* Not a domain, so done */
+			ReleaseSysCache(tup);
+			break;
+		}
+
 		/* Test for NOT NULL Constraint */
 		if (typTup->typnotnull)
 			notNull = true;
@@ -2010,14 +2020,7 @@ GetDomainConstraints(Oid typeOid)
 
 		systable_endscan(scan);
 
-		if (typTup->typtype != 'd')
-		{
-			/* Not a domain, so done */
-			ReleaseSysCache(tup);
-			break;
-		}
-
-		/* else loop to next domain in stack */
+		/* loop to next domain in stack */
 		typeOid = typTup->typbasetype;
 		ReleaseSysCache(tup);
 	}
-- 
2.11.0