The hstore typecast can be registered globally.

lib/extras.py

@@ -581,11 +581,47 @@ class HstoreAdapter(object):
 
     parse_unicode = classmethod(parse_unicode)
 
-def register_hstore(conn_or_curs, unicode=False):
+    def get_oids(self, conn_or_curs):
+        """Return the oid of the hstore and hstore[] types.
+
+        Return None if hstore is not available.
+        """
+        if hasattr(conn_or_curs, 'execute'):
+            conn = conn_or_curs.connection
+            curs = conn_or_curs
+        else:
+            conn = conn_or_curs
+            curs = conn_or_curs.cursor()
+
+        # Store the transaction status of the connection to revert it after use
+        conn_status = conn.status
+
+        # get the oid for the hstore
+        curs.execute("""\
+SELECT t.oid, typarray
+FROM pg_type t JOIN pg_namespace ns
+    ON typnamespace = ns.oid
+WHERE typname = 'hstore' and nspname = 'public';
+""")
+        oids = curs.fetchone()
+
+        # revert the status of the connection as before the command
+        if (conn_status != _ext.STATUS_IN_TRANSACTION
+        and conn.isolation_level != _ext.ISOLATION_LEVEL_AUTOCOMMIT):
+            conn.rollback()
+
+        return oids
+
+    get_oids = classmethod(get_oids)
+
+def register_hstore(conn_or_curs, globally=False, unicode=False):
     """Register adapter/typecaster for dict/hstore reading/writing.
 
-    The adapter must be registered on a connection or cursor as the hstore
-    oid is different in every database.
+    The function must receive a connection or cursor as the :sql:`hstore` oid
+    is different in every database. The typecaster will be registered only on
+    the connection or cursor passed as argument. If your application uses a
+    single database you can pass *globally*=True to have hstore registered on
+    all the connections.
 
     Raise `~psycopg2.ProgrammingError` if hstore is not installed in the
     target database.
@@ -593,30 +629,7 @@ def register_hstore(conn_or_curs, unicode=False):
     By default the returned dicts have string keys and values: use
     *unicode*=True to return `unicode` objects instead.
     """
-    if hasattr(conn_or_curs, 'execute'):
-        conn = conn_or_curs.connection
-        curs = conn_or_curs
-    else:
-        conn = conn_or_curs
-        curs = conn_or_curs.cursor()
-
-    # Store the transaction status of the connection to revert it after use
-    conn_status = conn.status
-
-    # get the oid for the hstore
-    curs.execute("""\
-SELECT t.oid, typarray
-FROM pg_type t JOIN pg_namespace ns
-    ON typnamespace = ns.oid
-WHERE typname = 'hstore' and nspname = 'public';
-""")
-    oids = curs.fetchone()
-
-    # revert the status of the connection as before the command
-    if (conn_status != _ext.STATUS_IN_TRANSACTION
-    and conn.isolation_level != _ext.ISOLATION_LEVEL_AUTOCOMMIT):
-        conn.rollback()
-
+    oids = HstoreAdapter.get_oids(conn_or_curs)
     if oids is None:
         raise psycopg2.ProgrammingError(
             "hstore type not found in the database. "
@@ -629,7 +642,7 @@ WHERE typname = 'hstore' and nspname = 'public';
         cast = HstoreAdapter.parse
 
     HSTORE = _ext.new_type((oids[0],), "HSTORE", cast)
-    _ext.register_type(HSTORE, conn_or_curs)
+    _ext.register_type(HSTORE, not globally and conn_or_curs or None)
     _ext.register_adapter(dict, HstoreAdapter)
 
 

tests/types_extras.py

@@ -222,6 +222,27 @@ class HstoreTestCase(unittest.TestCase):
         self.assert_(isinstance(t[2].keys()[0], unicode))
         self.assert_(isinstance(t[2].values()[0], unicode))
 
+    def test_register_globally(self):
+        from psycopg2.extras import register_hstore, HstoreAdapter
+
+        oids = HstoreAdapter.get_oids(self.conn)
+        try:
+            register_hstore(self.conn, globally=True)
+            conn2 = psycopg2.connect(self.conn.dsn)
+            cur2 = self.conn.cursor()
+            cur2.execute("select 'a => b'::hstore")
+            r = cur2.fetchone()
+            self.assert_(isinstance(r[0], dict))
+            conn2.close()
+        finally:
+            psycopg2.extensions.string_types.pop(oids[0])
+
+        # verify the caster is not around anymore
+        cur = self.conn.cursor()
+        cur.execute("select 'a => b'::hstore")
+        r = cur.fetchone()
+        self.assert_(isinstance(r[0], str))
+
     def test_roundtrip(self):
         from psycopg2.extras import register_hstore
         register_hstore(self.conn)