diff --git a/book.py b/book.py
index 56a4d35..2b4eb39 100644
--- a/book.py
+++ b/book.py
@@ -5,7 +5,7 @@
 
 from trytond.model import (
     Workflow, ModelView, ModelSQL, fields, Check, tree, Index)
-from trytond.pyson import Eval, Or, Bool, Id, Len
+from trytond.pyson import Eval, Or, Bool, Id
 from trytond.exceptions import UserError
 from trytond.i18n import gettext
 from trytond.transaction import Transaction
@@ -62,9 +62,9 @@ class Book(tree(separator='/'), Workflow, ModelSQL, ModelView):
         model_name='cashbook.type', ondelete='RESTRICT',
         states={
             'readonly': Or(
-                    STATES['readonly'],
-                    Len(Eval('lines')) > 0),
-        }, depends=DEPENDS+['lines'])
+                STATES['readonly'],
+                Eval('has_lines', False))},
+        depends=DEPENDS+['has_lines'])
     feature = fields.Function(fields.Char(
         string='Feature', readonly=True,
         states={'invisible': True}), 'on_change_with_feature')
@@ -86,6 +86,9 @@ class Book(tree(separator='/'), Workflow, ModelSQL, ModelView):
         string='Lines', field='cashbook',
         model_name='cashbook.line',
         states=STATES, depends=DEPENDS)
+    has_lines = fields.Function(fields.Boolean(
+        string='Has Lines', readonly=True, states={'invisible': True}),
+        'on_change_with_has_lines')
     reconciliations = fields.One2Many(
         string='Reconciliations',
         field='cashbook', model_name='cashbook.recon',
@@ -112,10 +115,10 @@ class Book(tree(separator='/'), Workflow, ModelSQL, ModelView):
         states={
             'readonly': Or(
                 STATES2['readonly'],
-                Len(Eval('lines')) > 0),
+                Eval('has_lines', False)),
             'invisible': STATES2['invisible'],
             'required': ~STATES2['invisible'],
-        }, depends=DEPENDS2+['lines'])
+        }, depends=DEPENDS2+['has_lines'])
 
     value_store = fields.One2Many(
         string='Values', model_name='cashbook.values', field='cashbook',
@@ -155,8 +158,8 @@ class Book(tree(separator='/'), Workflow, ModelSQL, ModelView):
         states={
             'readonly': Or(
                 STATES2['readonly'],
-                Len(Eval('lines', [])) > 0),
-        }, depends=DEPENDS2+['lines'])
+                Eval('has_lines', False))},
+        depends=DEPENDS2+['has_lines'])
     currency_digits = fields.Function(fields.Integer(
         string='Currency Digits',
         readonly=True), 'on_change_with_currency_digits')
@@ -543,6 +546,17 @@ class Book(tree(separator='/'), Workflow, ModelSQL, ModelView):
                         record[2], record[5], record[3])
         return result
 
+    @fields.depends('id')
+    def on_change_with_has_lines(self, name=None):
+        """ return True if cashbook has lines
+            (we dont use 'if self.lines:' this would slow down the client)
+        """
+        Line = Pool().get('cashbook.line')
+
+        if Line.search_count([('cashbook', '=', self.id)]):
+            return True
+        return False
+
     @fields.depends('btype')
     def on_change_with_feature(self, name=None):
         """ get feature-set