Reflect "NO ACTION" as None; support "RESTRICT"

The "NO ACTION" keyword for foreign key "ON UPDATE" is now considered to be
the default cascade for a foreign key on all supporting backends (SQlite,
MySQL, PostgreSQL) and when detected is not included in the reflection
dictionary; this is already the behavior for PostgreSQL and MySQL for all
previous SQLAlchemy versions in any case.   The "RESTRICT" keyword is
positively stored when detected; PostgreSQL does report on this keyword,
and MySQL as of version 8.0 does as well.  On earlier MySQL versions, it is
not reported by the database.

Fixes: #4741
Change-Id: I6becf1f2450605c1991158bb8a04d954dcc7396c

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/sqlalchemy/dialects/sqlite/base.py b/lib/sqlalchemy/dialects/sqlite/base.py
index d6a713988..b6ca8fe3c 100644
--- a/lib/sqlalchemy/dialects/sqlite/base.py
+++ b/lib/sqlalchemy/dialects/sqlite/base.py
@@ -1810,9 +1810,13 @@ class SQLiteDialect(default.DefaultDialect):
 
                 for token in re.split(r" *\bON\b *", onupdatedelete.upper()):
                     if token.startswith("DELETE"):
-                        options["ondelete"] = token[6:].strip()
+                        ondelete = token[6:].strip()
+                        if ondelete and ondelete != "NO ACTION":
+                            options["ondelete"] = ondelete
                     elif token.startswith("UPDATE"):
-                        options["onupdate"] = token[6:].strip()
+                        onupdate = token[6:].strip()
+                        if onupdate and onupdate != "NO ACTION":
+                            options["onupdate"] = onupdate
                 yield (
                     constraint_name,
                     constrained_columns,