The hstore typecast can be registered globally.

lib/extras.py

@@ -581,17 +581,10 @@ class HstoreAdapter(object):
 
     parse_unicode = classmethod(parse_unicode)
 
-def register_hstore(conn_or_curs, unicode=False):
+    def get_oids(self, conn_or_curs):
-    """Register adapter/typecaster for dict/hstore reading/writing.
+        """Return the oid of the hstore and hstore[] types.
 
-    The adapter must be registered on a connection or cursor as the hstore
+        Return None if hstore is not available.
-    oid is different in every database.
-
-    Raise `~psycopg2.ProgrammingError` if hstore is not installed in the
-    target database.
-
-    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
@@ -617,6 +610,26 @@ WHERE typname = 'hstore' and nspname = 'public';
         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 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.
+
+    By default the returned dicts have string keys and values: use
+    *unicode*=True to return `unicode` objects instead.
+    """
+    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)