Create connection characteristics API; implement postgresql flags

Added support for PostgreSQL "readonly" and "deferrable" flags for all of
psycopg2, asyncpg and pg8000 dialects.   This takes advantage of a newly
generalized version of the "isolation level" API to support other kinds of
session attributes set via execution options that are reliably reset
when connections are returned to the connection pool.

Fixes: #5549
Change-Id: I0ad6d7a095e49d331618274c40ce75c76afdc7dd

1 files changed, 19 insertions, 1 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/asyncpg.py b/lib/sqlalchemy/dialects/postgresql/asyncpg.py
index 515ef6e28..eb87249b4 100644
--- a/lib/sqlalchemy/dialects/postgresql/asyncpg.py
+++ b/lib/sqlalchemy/dialects/postgresql/asyncpg.py
@@ -465,6 +465,8 @@ class AsyncAdapt_asyncpg_connection:
         "dbapi",
         "_connection",
         "isolation_level",
+        "readonly",
+        "deferrable",
         "_transaction",
         "_started",
     )
@@ -475,6 +477,8 @@ class AsyncAdapt_asyncpg_connection:
         self.dbapi = dbapi
         self._connection = connection
         self.isolation_level = "read_committed"
+        self.readonly = False
+        self.deferrable = False
         self._transaction = None
         self._started = False
         self.await_(self._setup_type_codecs())
@@ -530,7 +534,9 @@ class AsyncAdapt_asyncpg_connection:
 
         try:
             self._transaction = self._connection.transaction(
-                isolation=self.isolation_level
+                isolation=self.isolation_level,
+                readonly=self.readonly,
+                deferrable=self.deferrable,
             )
             await self._transaction.start()
         except Exception as error:
@@ -763,6 +769,18 @@ class PGDialect_asyncpg(PGDialect):
 
         connection.set_isolation_level(level)
 
+    def set_readonly(self, connection, value):
+        connection.readonly = value
+
+    def get_readonly(self, connection):
+        return connection.readonly
+
+    def set_deferrable(self, connection, value):
+        connection.deferrable = value
+
+    def get_deferrable(self, connection):
+        return connection.deferrable
+
     def create_connect_args(self, url):
         opts = url.translate_connect_args(username="user")
         if "port" in opts: