1 files changed, 11 insertions, 2 deletions
diff --git a/model.py b/model.py
index 45e9296..02323b9 100644
--- a/model.py
+++ b/model.py
@@ -1,5 +1,5 @@
 import elixir
-from elixir import Field, ManyToOne, ColumnProperty, using_options, using_options_defaults
+from elixir import Field, ManyToOne, OneToMany, OneToOne, ColumnProperty, using_options, using_options_defaults
 from sqlalchemy import types as T
 
 from functools import partial
@@ -18,8 +18,14 @@ class Category (Entity):
     
     name = Field(T.String(50), unique = True)
 
+    parent = ManyToOne('Category')
+    children = OneToMany('Category')
+
     def __repr__ (self):
-        return '<Category "%s">' % self.name
+        if self.parent:
+            return '<Category "%s" of "%s">' % (self.name, self.parent.name)
+        else:
+            return '<Category "%s">' % self.name
 
 class Expense (Entity):
     using_options(abstract = True)
@@ -38,6 +44,9 @@ class ConstExpense (Expense):
 
     monthly = ColumnProperty(lambda c: c.expense / c.months)
 
+    next = OneToOne('ConstExpense', inverse = 'prev')
+    prev = ManyToOne('ConstExpense')
+
 elixir.setup_all()
 
 session = elixir.session