Include all columns in default names for foreign key constraints

When creating a name for a foreign key constraint when none is
specified, use all column names instead of only the first one, similar
to how it is already done for index names.

Author: Paul Martinez <hellopfm@gmail.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/CAF+2_SFjky6XRfLNRXpkG97W6PRbOO_mjAxqXzAAimU=c7w7_A@mail.gmail.com

Author: petere

src/backend/commands/indexcmds.c

@@ -2109,7 +2109,8 @@ ChooseIndexName(const char *tabname, Oid namespaceId,
  * We know that less than NAMEDATALEN characters will actually be used,
  * so we can truncate the result once we've generated that many.
  *
- * XXX See also ChooseExtendedStatisticNameAddition.
+ * XXX See also ChooseForeignKeyConstraintNameAddition and
+ * ChooseExtendedStatisticNameAddition.
  */
 static char *
 ChooseIndexNameAddition(List *colnames)

src/backend/commands/statscmds.c

@@ -498,7 +498,8 @@ ChooseExtendedStatisticName(const char *name1, const char *name2,
  * We know that less than NAMEDATALEN characters will actually be used,
  * so we can truncate the result once we've generated that many.
  *
- * XXX see also ChooseIndexNameAddition.
+ * XXX see also ChooseForeignKeyConstraintNameAddition and
+ * ChooseIndexNameAddition.
  */
 static char *
 ChooseExtendedStatisticNameAddition(List *exprs)

src/backend/commands/tablecmds.c

@@ -402,6 +402,7 @@ static ObjectAddress ATExecAddConstraint(List **wqueue,
 					AlteredTableInfo *tab, Relation rel,
 					Constraint *newConstraint, bool recurse, bool is_readd,
 					LOCKMODE lockmode);
+static char *ChooseForeignKeyConstraintNameAddition(List *colnames);
 static ObjectAddress ATExecAddIndexConstraint(AlteredTableInfo *tab, Relation rel,
 						 IndexStmt *stmt, LOCKMODE lockmode);
 static ObjectAddress ATAddCheckConstraint(List **wqueue,
@@ -7191,7 +7192,7 @@ ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 			else
 				newConstraint->conname =
 					ChooseConstraintName(RelationGetRelationName(rel),
-										 strVal(linitial(newConstraint->fk_attrs)),
+										 ChooseForeignKeyConstraintNameAddition(newConstraint->fk_attrs),
 										 "fkey",
 										 RelationGetNamespace(rel),
 										 NIL);
@@ -7210,6 +7211,45 @@ ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	return address;
 }
 
+/*
+ * Generate the column-name portion of the constraint name for a new foreign
+ * key given the list of column names that reference the referenced
+ * table.  This will be passed to ChooseConstraintName along with the parent
+ * table name and the "fkey" suffix.
+ *
+ * We know that less than NAMEDATALEN characters will actually be used, so we
+ * can truncate the result once we've generated that many.
+ *
+ * XXX see also ChooseExtendedStatisticNameAddition and
+ * ChooseIndexNameAddition.
+ */
+static char *
+ChooseForeignKeyConstraintNameAddition(List *colnames)
+{
+	char		buf[NAMEDATALEN * 2];
+	int			buflen = 0;
+	ListCell   *lc;
+
+	buf[0] = '\0';
+	foreach(lc, colnames)
+	{
+		const char *name = strVal(lfirst(lc));
+
+		if (buflen > 0)
+			buf[buflen++] = '_';	/* insert _ between names */
+
+		/*
+		 * At this point we have buflen <= NAMEDATALEN.  name should be less
+		 * than NAMEDATALEN already, but use strlcpy for paranoia.
+		 */
+		strlcpy(buf + buflen, name, NAMEDATALEN);
+		buflen += strlen(buf + buflen);
+		if (buflen >= NAMEDATALEN)
+			break;
+	}
+	return pstrdup(buf);
+}
+
 /*
  * Add a check constraint to a single table and its children.  Returns the
  * address of the constraint added to the parent relation, if one gets added,

src/test/regress/expected/alter_table.out

@@ -655,26 +655,26 @@ CREATE TEMP TABLE PKTABLE (ptest1 int, ptest2 inet,
 -- This should fail, because we just chose really odd types
 CREATE TEMP TABLE FKTABLE (ftest1 cidr, ftest2 timestamp);
 ALTER TABLE FKTABLE ADD FOREIGN KEY(ftest1, ftest2) references pktable;
-ERROR:  foreign key constraint "fktable_ftest1_fkey" cannot be implemented
+ERROR:  foreign key constraint "fktable_ftest1_ftest2_fkey" cannot be implemented
 DETAIL:  Key columns "ftest1" and "ptest1" are of incompatible types: cidr and integer.
 DROP TABLE FKTABLE;
 -- Again, so should this...
 CREATE TEMP TABLE FKTABLE (ftest1 cidr, ftest2 timestamp);
 ALTER TABLE FKTABLE ADD FOREIGN KEY(ftest1, ftest2)
      references pktable(ptest1, ptest2);
-ERROR:  foreign key constraint "fktable_ftest1_fkey" cannot be implemented
+ERROR:  foreign key constraint "fktable_ftest1_ftest2_fkey" cannot be implemented
 DETAIL:  Key columns "ftest1" and "ptest1" are of incompatible types: cidr and integer.
 DROP TABLE FKTABLE;
 -- This fails because we mixed up the column ordering
 CREATE TEMP TABLE FKTABLE (ftest1 int, ftest2 inet);
 ALTER TABLE FKTABLE ADD FOREIGN KEY(ftest1, ftest2)
      references pktable(ptest2, ptest1);
-ERROR:  foreign key constraint "fktable_ftest1_fkey" cannot be implemented
+ERROR:  foreign key constraint "fktable_ftest1_ftest2_fkey" cannot be implemented
 DETAIL:  Key columns "ftest1" and "ptest2" are of incompatible types: integer and inet.
 -- As does this...
 ALTER TABLE FKTABLE ADD FOREIGN KEY(ftest2, ftest1)
      references pktable(ptest1, ptest2);
-ERROR:  foreign key constraint "fktable_ftest2_fkey" cannot be implemented
+ERROR:  foreign key constraint "fktable_ftest2_ftest1_fkey" cannot be implemented
 DETAIL:  Key columns "ftest2" and "ptest1" are of incompatible types: inet and integer.
 DROP TABLE FKTABLE;
 DROP TABLE PKTABLE;