Refine domain nullable rules for PostgreSQL reflection

Fixed issue in PostgreSQL reflection where a column expressing "NOT NULL"
will supersede the nullability of a corresponding domain.

Fixes #6161

Change-Id: I1a3de49afcdb952f71bd7a7cc7b264513c93eff5

1 files changed, 3 insertions, 2 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index 6e6f5513d..ba7774590 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -3767,8 +3767,9 @@ class PGDialect(default.DefaultDialect):
                 attype, is_array = _handle_array_type(attype)
                 # strip quotes from case sensitive enum or domain names
                 enum_or_domain_key = tuple(util.quoted_token_parser(attype))
-                # A table can't override whether the domain is nullable.
-                nullable = domain["nullable"]
+                # A table can't override a not null on the domain,
+                # but can override nullable
+                nullable = nullable and domain["nullable"]
                 if domain["default"] and not default:
                     # It can, however, override the default
                     # value, but can't set it to null.