[FIX] fields: allow overriding of a old-api function field

When overriding a field defined as a function field, the field must either
create a corresponding column that is not a fields.function (if stored), or
have no corresponding column (if not stored).

openerp/fields.py

@@ -637,8 +637,11 @@ class Field(object):
     #
 
     def to_column(self):
-        """ return a low-level field object corresponding to `self` """
-        assert self.store or self.column
+        """ Return a column object corresponding to `self`, or ``None``. """
+        if not self.store and self.compute:
+            # non-stored computed fields do not have a corresponding column
+            self.column = None
+            return None
 
         # determine column parameters
         #_logger.debug("Create fields._column for Field %s", self)
@@ -674,6 +677,7 @@ class Field(object):
     _column_groups = property(attrgetter('groups'))
     _column_change_default = property(attrgetter('change_default'))
     _column_deprecated = property(attrgetter('deprecated'))
+    _column_compute = property(lambda self: bool(self.compute))
 
     ############################################################################
     #

openerp/models.py

@@ -2986,8 +2986,9 @@ class BaseModel(object):
         cls._columns = {}
         for name, field in cls._fields.iteritems():
             field.setup(self.env)
-            if field.store or field.column:
-                cls._columns[name] = field.to_column()
+            column = field.to_column()
+            if column:
+                cls._columns[name] = column
 
         # group fields by compute to determine field.computed_fields
         fields_by_compute = defaultdict(list)

openerp/osv/fields.py

@@ -1293,9 +1293,14 @@ class function(_column):
                 self._symbol_set = type_class._symbol_set
 
     def new(self, **args):
-        # HACK: function fields are tricky to recreate, simply return a copy
-        import copy
-        return copy.copy(self)
+        if args.get('compute'):
+            # field is computed, we need an instance of the given type
+            type_class = globals()[self._type]
+            return type_class(**args)
+        else:
+            # HACK: function fields are tricky to recreate, simply return a copy
+            import copy
+            return copy.copy(self)
 
     def to_field_args(self):
         args = super(function, self).to_field_args()