diff --git a/README.rst b/README.rst
index 7b12126..49aa477 100644
--- a/README.rst
+++ b/README.rst
@@ -9,11 +9,11 @@ pip install mds-cashbook-bookcategory
 
 Requires
 ========
-- Tryton 6.0
+- Tryton 6.8
 
 Changes
 =======
 
-*6.0.0 - 07.11.2022*
+*6.8.4 - 05.06.2023*
 
-- init
+- code optimized, porting to Tryton 6.8
diff --git a/book.py b/book.py
index 00a2d5e..ee219a4 100644
--- a/book.py
+++ b/book.py
@@ -22,10 +22,10 @@ class CategoryCashbookRel(ModelSQL):
     __name__ = 'cashbook.bookcategory-rel'
 
     category = fields.Many2One(
-        string='Category', required=True, select=True,
+        string='Category', required=True,
         model_name='cashbook.bookcategory', ondelete='CASCADE')
     cashbook = fields.Many2One(
-        string='Cashbook', required=True, select=True,
+        string='Cashbook', required=True,
         model_name='cashbook.book', ondelete='CASCADE')
 
 # end CategoryCashbookRel
diff --git a/category.py b/category.py
index b428e51..7b97dcb 100644
--- a/category.py
+++ b/category.py
@@ -17,7 +17,7 @@ class Category(tree(separator=' / '), ModelSQL, ModelView):
     name = fields.Char(string='Name', required=True, translate=True)
 
     parent = fields.Many2One(
-        string='Parent', select=True,
+        string='Parent',
         model_name='cashbook.bookcategory', ondelete='CASCADE')
     childs = fields.One2Many(
         string='Children', field='parent',
diff --git a/setup.py b/setup.py
index 728ff37..23a7db4 100644
--- a/setup.py
+++ b/setup.py
@@ -40,7 +40,7 @@ with open(path.join(here, 'versiondep.txt'), encoding='utf-8') as f:
 
 # tryton-version
 major_version = 6
-minor_version = 0
+minor_version = 8
 
 requires = []
 for dep in info.get('depends', []):
@@ -89,6 +89,7 @@ setup(name='%s_%s' % (PREFIX, MODULE),
     'License :: OSI Approved :: GNU General Public License (GPL)',
     'Programming Language :: Python :: 3.7',
     'Programming Language :: Python :: 3.8',
+    'Programming Language :: Python :: 3.9',
     ],
 
     keywords='tryton cashbook category',
diff --git a/tests/__init__.py b/tests/__init__.py
index a6930ba..cf7e957 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -2,25 +2,3 @@
 # This file is part of the cashbook-module from m-ds for Tryton.
 # The COPYRIGHT file at the top level of this repository contains the
 # full copyright notices and license terms.
-
-import trytond.tests.test_tryton
-import unittest
-
-from .test_category import CategoryTestCase
-
-
-__all__ = ['suite']
-
-
-class CashbookCategoryTestCase(CategoryTestCase):
-    'Test cashbook module'
-    module = 'cashbook_bookcategory'
-
-# end CashbookCategoryTestCase
-
-
-def suite():
-    suite = trytond.tests.test_tryton.suite()
-    suite.addTests(unittest.TestLoader().loadTestsFromTestCase(
-        CashbookCategoryTestCase))
-    return suite
diff --git a/tests/test_category.py b/tests/test_category.py
index 4bf63d5..ddc689d 100644
--- a/tests/test_category.py
+++ b/tests/test_category.py
@@ -6,7 +6,7 @@
 from trytond.tests.test_tryton import with_transaction
 from trytond.pool import Pool
 from trytond.transaction import Transaction
-from trytond.modules.cashbook.tests import CashbookTestCase
+from trytond.modules.cashbook.tests.test_module import CashbookTestCase
 
 
 class CategoryTestCase(CashbookTestCase):
@@ -98,3 +98,6 @@ class CategoryTestCase(CashbookTestCase):
             self.assertEqual(len(book.categories), 0)
 
 # end CategoryTestCase
+
+
+del CashbookTestCase
diff --git a/tryton.cfg b/tryton.cfg
index ba1dc2c..458dffc 100644
--- a/tryton.cfg
+++ b/tryton.cfg
@@ -1,5 +1,5 @@
 [tryton]
-version=6.0.0
+version=6.8.4
 depends:
     cashbook
 xml:
diff --git a/versiondep.txt b/versiondep.txt
index e56514a..4191fe8 100644
--- a/versiondep.txt
+++ b/versiondep.txt
@@ -1,2 +1,2 @@
-cashbook;6.0.19;6.0.999;mds
+cashbook;6.8.28;6.8.999;mds