modified model metaclass to replace column definitions with properties that modify the columns value member instead of removing them until instantiation

cassandraengine/columns.py

@@ -21,6 +21,8 @@ class BaseColumn(object):
         self.default = default
         self.null = null
 
+        self.value = None
+
     def validate(self, value):
         """
         Returns a cleaned and validated value. Raises a ValidationError
@@ -40,6 +42,14 @@ class BaseColumn(object):
         """
         return value
 
+    def to_database(self, value):
+        """
+        Converts python value into database value
+        """
+        if value is None and self.has_default:
+            return self.get_default()
+        return value
+
     @property
     def has_default(self):
         return bool(self.default)
@@ -48,6 +58,33 @@ class BaseColumn(object):
     def is_primary_key(self):
         return self.primary_key
 
+    #methods for replacing column definitions with properties that interact
+    #with a column's value member
+    #this will allow putting logic behind value access (lazy loading, etc)
+    def _getval(self):
+        """ This columns value getter """
+        return self.value
+
+    def _setval(self, val):
+        """ This columns value setter """
+        self.value = val
+
+    def _delval(self):
+        """ This columns value deleter """
+        raise NotImplementedError
+
+    def get_property(self, allow_delete=True):
+        """
+        Returns the property object that will set and get this
+        column's value and be assigned to this column's model attribute
+        """
+        getval = lambda slf: self._getval()
+        setval = lambda slf, val: self._setval(val)
+        delval = lambda slf: self._delval()
+        if not allow_delete:
+            return property(getval, setval)
+        return property(getval, setval, delval)
+
     def get_default(self):
         if self.has_default:
             if callable(self.default):
@@ -55,14 +92,6 @@ class BaseColumn(object):
             else:
                 return self.default
 
-    def to_database(self, value):
-        """
-        Converts python value into database value
-        """
-        if value is None and self.has_default:
-            return self.get_default()
-        return value
-
     def get_column_def(self):
         """
         Returns a column definition for CQL table definition

cassandraengine/models.py

@@ -32,7 +32,7 @@ class BaseModel(object):
 
     @property
     def pk(self):
-        """ Returns the object's primary key, regardless of it's name """
+        """ Returns the object's primary key """
         return getattr(self, self._pk_name)
 
     #dynamic column methods
@@ -78,26 +78,31 @@ class ModelMetaClass(type):
         #and set default column names
         _columns = {}
         pk_name = None
+
+        def _transform_column(col_name, col_obj):
+            _columns[col_name] = col_obj
+            col_obj.set_db_name(col_name)
+            allow_delete = not col_obj.primary_key
+            attrs[col_name] = col_obj.get_property(allow_delete=allow_delete)
+
+        #transform column definitions
         for k,v in attrs.items():
             if isinstance(v, columns.BaseColumn):
                 if v.is_primary_key:
                     if pk_name:
                         raise ModelException("More than one primary key defined for {}".format(name))
                     pk_name = k
-                _columns[k] = attrs.pop(k)
-                _columns[k].set_db_name(k)
+                _transform_column(k,v)
 
         #set primary key if it's not already defined
         if not pk_name:
-            _columns['id'] = columns.UUID(primary_key=True)
-            _columns['id'].set_db_name('id')
-            pk_name = 'id'
+            k,v = 'id', columns.UUID(primary_key=True)
+            _transform_column(k,v)
+            pk_name = k
         
-        #setup pk shortcut
+        #setup primary key shortcut
         if pk_name != 'pk':
-            pk_get = lambda self: getattr(self, pk_name)
-            pk_set = lambda self, val: setattr(self, pk_name, val)
-            attrs['pk'] = property(pk_get, pk_set)
+            attrs['pk'] = _columns[pk_name].get_property(allow_delete=False)
 
         #check for duplicate column names
         col_names = set()
@@ -107,7 +112,7 @@ class ModelMetaClass(type):
             col_names.add(v.db_field)
 
         #get column family name
-        cf_name = attrs.pop('db_name', None) or name
+        cf_name = attrs.pop('db_name', name)
 
         #create db_name -> model name map for loading
         db_map = {}

cassandraengine/tests/model/test_class_construction.py

@@ -19,8 +19,8 @@ class TestModelClassFunction(BaseCassEngTestCase):
             text = columns.Text()
 
         self.assertHasAttr(TestModel, '_columns')
-        self.assertNotHasAttr(TestModel, 'id')
-        self.assertNotHasAttr(TestModel, 'text')
+        self.assertHasAttr(TestModel, 'id')
+        self.assertHasAttr(TestModel, 'text')
 
         inst = TestModel()
         self.assertHasAttr(inst, 'id')