diff --git a/trytond/ir/action.py b/trytond/ir/action.py
index 66e47ede54..dbca24a278 100644
--- a/trytond/ir/action.py
+++ b/trytond/ir/action.py
@@ -171,10 +171,13 @@ class ActionReport(OSV):
         fnct_inv='report_content_inv', type='binary',
         string='Content')
     action = fields.Many2One('ir.action', 'Action', required=True)
-    _sql_constraints = [
-        ('report_name_uniq', 'unique (report_name)',
-            'The internal name must be unique!'),
-    ]
+
+    def __init__(self):
+        super(ActionReport, self).__init__()
+        self._sql_constraints += [
+            ('report_name_uniq', 'unique (report_name)',
+                'The internal name must be unique!'),
+        ]
 
     def default_type(self, cursor, user, context=None):
         return 'ir.action.report'
diff --git a/trytond/ir/attachment.py b/trytond/ir/attachment.py
index dc50b7fcdc..0f926da038 100644
--- a/trytond/ir/attachment.py
+++ b/trytond/ir/attachment.py
@@ -22,11 +22,14 @@ class Attachment(OSV):
     collision = fields.Integer('Collision')
     datas_size = fields.Function('datas', type='integer',
        string='Datas size')
-    _sql_constraints = [
-        ('res_model_res_id_name',
-            'UNIQUE (res_model, res_id, name)',
-            'Error! You can not create attachment with the same name!'),
-    ]
+
+    def __init__(self):
+        super(Attachment, self).__init__()
+        self._sql_constraints += [
+            ('res_model_res_id_name',
+                'UNIQUE (res_model, res_id, name)',
+                'Error! You can not create attachment with the same name!'),
+        ]
 
     def default_collision(self, cursor, user, context=None):
         return 0
diff --git a/trytond/ir/model.py b/trytond/ir/model.py
index 2bfb3c58fd..391c9c306e 100644
--- a/trytond/ir/model.py
+++ b/trytond/ir/model.py
@@ -66,10 +66,13 @@ class ModelAccess(OSV):
     perm_create = fields.Boolean('Create Access')
     perm_unlink = fields.Boolean('Delete Permission')
     description = fields.Text('Description')
-    _sql_constraints = [
-        ('model_group_uniq', 'UNIQUE("model", "group")',
-            'Only on record by model and group is allowed!'),
-    ]
+
+    def __init__(self):
+        super(ModelAccess, self).__init__()
+        self._sql_constraints += [
+            ('model_group_uniq', 'UNIQUE("model", "group")',
+                'Only on record by model and group is allowed!'),
+        ]
 
     def check(self, cursor, user, model_name, mode='read',
             raise_exception=True):
@@ -158,19 +161,16 @@ class ModelData(OSV):
     date_update = fields.DateTime('Update Date')
     date_init = fields.DateTime('Init Date')
     values = fields.Text('Values')
-    _sql_constraints = [
-        ('fs_id_module_uniq', 'UNIQUE("fs_id", "module")',
-            'The couple (fs_id, module) must be unique!'),
-    ]
-
-    def default_date_init(self, cursor, user, context=None):
-        return time.strftime('%Y-%m-%d %H:%M:%S')
 
     def __init__(self):
         super(ModelData, self).__init__()
-        self.fs2db = None
-        self.fs2values = None
+        self._sql_constraints = [
+            ('fs_id_module_uniq', 'UNIQUE("fs_id", "module")',
+                'The couple (fs_id, module) must be unique!'),
+        ]
 
+    def default_date_init(self, cursor, user, context=None):
+        return time.strftime('%Y-%m-%d %H:%M:%S')
 
     def get_id(self, cursor, user, module, fs_id):
         """
diff --git a/trytond/ir/module/module.py b/trytond/ir/module/module.py
index caa1d3ec51..687b7279f9 100644
--- a/trytond/ir/module/module.py
+++ b/trytond/ir/module/module.py
@@ -149,10 +149,13 @@ class Module(OSV):
         ('Other proprietary', 'Other proprietary')], string='License',
         readonly=True)
     _order = 'name'
-    _sql_constraints = [
-        ('name_uniq', 'unique (name)',
-            'The name of the module must be unique!'),
-    ]
+
+    def __init__(self):
+        super(Module, self).__init__()
+        self._sql_constraints = [
+            ('name_uniq', 'unique (name)',
+                'The name of the module must be unique!'),
+        ]
 
     def default_state(self, cursor, user, context=None):
         return 'uninstalled'
diff --git a/trytond/ir/translation.py b/trytond/ir/translation.py
index f111d1e5f0..9dd82a6b23 100644
--- a/trytond/ir/translation.py
+++ b/trytond/ir/translation.py
@@ -40,15 +40,18 @@ class Translation(OSV, Cacheable):
     fuzzy = fields.Boolean('Fuzzy')
     model = fields.Function('get_model', fnct_search='model_search',
        type='char', string='Model')
-    _sql_constraints = [
-        ('translation_uniq', 'UNIQUE (name, res_id, lang, type, src)',
-            'Translation must be unique'),
-    ]
     _sql = """
         CREATE INDEX ir_translation_ltn ON ir_translation (lang, type, name);
         CREATE INDEX ir_translation_res_id ON ir_translation (res_id);
     """
 
+    def __init__(self):
+        super(Translation, self).__init__()
+        self._sql_constraints += [
+            ('translation_uniq', 'UNIQUE (name, res_id, lang, type, src)',
+                'Translation must be unique'),
+        ]
+
     def default_fuzzy(self, cursor, user, context=None):
         return 0
 
diff --git a/trytond/ir/ui/view.py b/trytond/ir/ui/view.py
index 640c568c12..6813c930f9 100644
--- a/trytond/ir/ui/view.py
+++ b/trytond/ir/ui/view.py
@@ -21,9 +21,12 @@ class View(OSV):
     field_childs = fields.Char('Childs Field',size=64)
     module = fields.Char('Module', size=128, readonly=True)
     _order = "priority"
-    _constraints = [
-        ('check_xml', 'Invalid XML for View Architecture!', ['arch'])
-    ]
+
+    def __init__(self):
+        super(View, self).__init__()
+        self._constraints += [
+            ('check_xml', 'Invalid XML for View Architecture!', ['arch'])
+        ]
 
     def default_arch(self, cursor, user, context=None):
         return '<?xml version="1.0"?>\n' \
diff --git a/trytond/osv/orm.py b/trytond/osv/orm.py
index c896658de2..865f0e9d36 100644
--- a/trytond/osv/orm.py
+++ b/trytond/osv/orm.py
@@ -235,8 +235,6 @@ class ORM(object):
             - relations (one2many, many2one, many2many)
             - functions
     """
-    _sql_constraints = []
-    _constraints = []
     _log_access = True
     _table = None
     _name = None
@@ -244,13 +242,12 @@ class ORM(object):
     _parent_name = 'parent'
     _date_name = 'date'
     _order = 'id'
-    _inherits = {}
+    _inherits = {} #XXX remove from class instance
     _sequence = None
     _description = ''
     _auto = True
     _obj = None
     _sql = ''
-    _inherit_fields = []
     pool = None
     __columns = None
     __defaults = None
@@ -769,10 +766,13 @@ class ORM(object):
                 'import_data',
                 'search_count',
                 ]
-
-        # reinit the cachel on _columns and _defaults
+        self._sql_constraints = []
+        self._constraints = []
+        self._inherit_fields = []
+        # reinit the cache on _columns and _defaults
         self.__columns = None
         self.__defaults = None
+
         if not self._table:
             self._table = self._name.replace('.', '_')
         if not self._description:
diff --git a/trytond/res/group.py b/trytond/res/group.py
index 7453738299..ed9919ba4a 100644
--- a/trytond/res/group.py
+++ b/trytond/res/group.py
@@ -14,9 +14,12 @@ class Group(OSV):
        domain="[('global', '<>', True)]")
     menu_access = fields.Many2Many('ir.ui.menu', 'ir_ui_menu_group_rel',
        'gid', 'menu_id', 'Access Menu')
-    _sql_constraints = [
-        ('name_uniq', 'unique (name)', 'The name of the group must be unique!')
-    ]
+
+    def __init__(self):
+        super(Group, self).__init__()
+        self._sql_constraints += [
+            ('name_uniq', 'unique (name)', 'The name of the group must be unique!')
+        ]
 
     def write(self, cursor, user, ids, vals, context=None):
         res = super(Group, self).write(cursor, user, ids, vals,
diff --git a/trytond/res/user.py b/trytond/res/user.py
index bc1e526eba..88581cc838 100644
--- a/trytond/res/user.py
+++ b/trytond/res/user.py
@@ -27,22 +27,30 @@ class User(OSV):
        domain="[('global', '<>', True)]")
     language = fields.Selection('languages', 'Language')
     timezone = fields.Selection('timezones', 'Timezone')
-    _sql_constraints = [
-        ('login_key', 'UNIQUE (login)',
-            'You can not have two users with the same login!')
-    ]
-    _preferences_fields = [
-        'name',
-        'password',
-        'signature',
-        'menu',
-        'action',
-    ]
-    _context_fields = [
-        'language',
-        'timezone',
-        'groups',
-    ]
+
+    def __init__(self):
+        super(User, self).__init__()
+        self._rpc_allowed += [
+            'get_preferences',
+            'set_preferences',
+            'get_preferences_fields_view',
+        ]
+        self._sql_constraints = [
+            ('login_key', 'UNIQUE (login)',
+                'You can not have two users with the same login!')
+        ]
+        self._preferences_fields = [
+            'name',
+            'password',
+            'signature',
+            'menu',
+            'action',
+        ]
+        self._context_fields = [
+            'language',
+            'timezone',
+            'groups',
+        ]
 
     def default_password(self, cursor, user, context=None):
         return ''
@@ -68,14 +76,6 @@ class User(OSV):
     def default_action(self, cursor, user, context=None):
         return self.default_menu(cursor, user, context=context)
 
-    def __init__(self):
-        super(User, self).__init__()
-        self._rpc_allowed += [
-            'get_preferences',
-            'set_preferences',
-            'get_preferences_fields_view',
-        ]
-
     def _convert_vals(self, cursor, user, vals, context=None):
         vals = vals.copy()
         action_obj = self.pool.get('ir.action')
diff --git a/trytond/webdav/webdav.py b/trytond/webdav/webdav.py
index 92b2c7dc52..a71c152323 100644
--- a/trytond/webdav/webdav.py
+++ b/trytond/webdav/webdav.py
@@ -16,22 +16,25 @@ class Directory(OSV):
     childs = fields.One2Many('webdav.directory', 'parent', 'Childs')
     model = fields.Many2One('ir.model', 'Model')
     domain = fields.Char('Domain', size=250)
-    _sql_constraints = [
-        ('name_parent_uniq', 'UNIQUE (name, parent)',
-            'The directory name must be unique inside a directory!'),
-    ]
     _parent_name = 'parent'
-    _constraints = [
-        ('check_recursion',
-            'Error! You can not create recursive directories.', ['parent']),
-        ('check_attachment',
-            'Error! You can not create a directory \n' \
-                    'with the same name of an existing file \n' \
-                    'inside the same directory.', ['name']),
-    ]
-    ext2mime = {
-        '.png': 'image/png',
-    }
+
+    def __init__(self):
+        super(Directory, self).__init__()
+        self._sql_constraints += [
+            ('name_parent_uniq', 'UNIQUE (name, parent)',
+                'The directory name must be unique inside a directory!'),
+        ]
+        self._constraints += [
+            ('check_recursion',
+                'Error! You can not create recursive directories.', ['parent']),
+            ('check_attachment',
+                'Error! You can not create a directory \n' \
+                        'with the same name of an existing file \n' \
+                        'inside the same directory.', ['name']),
+        ]
+        self.ext2mime = {
+            '.png': 'image/png',
+        }
 
     def default_domain(self, cursor, user, context=None):
         return '[]'
@@ -299,7 +302,7 @@ class Attachment(OSV):
 
     def __init__(self):
         super(Attachment, self).__init__()
-        self._constraints = self._constraints + [
+        self._constraints += [
             ('check_directory',
                 'Error! You can not create a attachment \n' \
                         'on a directory that have the same name \n' \