debugged and optimized cascading delete, issue datajoint#15

datajoint/relation.py

@@ -209,31 +209,32 @@ def delete(self):
         relations = self.descendants
         restrict_by_me = set()
         for r in relations:
-            for ref in r.references:
-                restrict_by_me.add(ref)
+            restrict_by_me.update(r.references)
         relations = OrderedDict((r.full_table_name, r) for r in relations)
 
         if self.restrictions:
             restrict_by_me.add(self.full_table_name)
             relations[self.full_table_name] &= self.restrictions
 
-        for r in relations.values():
+        for name in relations:
+            r = relations[name]
             for dep in (r.children + r.references):
-                relations[dep] &= r.project() if r.full_table_name in restrict_by_me else r.restrictions
-
-        if config['safemode']:
-            do_delete = False # indicate if there is anything to delete
-            print('The contents of the following tables are about to be deleted:')
-            for relation in relations.values():
-                count = len(relation)
-                if count:
-                    do_delete = True
+                relations[dep] &= r.project() if name in restrict_by_me else r.restrictions
+
+        do_delete = False # indicate if there is anything to delete
+        print('The contents of the following tables are about to be deleted:')
+        for relation in relations.values():
+            count = len(relation)
+            if count:
+                do_delete = True
+                if config['safemode']:
                     print(relation.full_table_name, '(%d tuples)' % count)
-            if not do_delete or user_choice("Proceed?", default='no') != 'yes':
-                return
-        with self.connection.transaction:
-            for r in reversed(list(relations.values())):
-                r.delete_quick()
+            else:
+                relations.pop(relation.full_table_name)
+        if do_delete and (not config['safemode'] or user_choice("Proceed?", default='no') == 'yes'):
+            with self.connection.transaction:
+                for r in reversed(list(relations.values())):
+                    r.delete_quick()
 
     def drop_quick(self):
         """

datajoint/relational_operand.py

@@ -132,8 +132,9 @@ def __sub__(self, restriction):
         """
         return self & Not(restriction)
 
+    @abc.abstractmethod
     def _repr_helper(self):
-        return "None"
+        pass
 
     def __repr__(self):
         ret = self._repr_helper()
@@ -286,7 +287,7 @@ def select_fields(self):
 
 
 class Projection(RelationalOperand):
-    def __init__(self, arg, *attributes, _aggregate=False, **renamed_attributes):
+    def __init__(self, arg, *attributes, **renamed_attributes):
         """
         See RelationalOperand.project()
         """
@@ -302,14 +303,16 @@ def __init__(self, arg, *attributes, _aggregate=False, **renamed_attributes):
                 self._renamed_attributes.update({d['alias']: d['sql_expression']})
             else:
                 self._attributes.append(attribute)
-        self._aggregate = _aggregate
 
         if arg.heading.computed:
             self._arg = Subquery(arg)
         else:
             self._arg = arg
             self._restrictions = arg.restrictions
 
+    def _repr_helper(self):
+        return "(%r).project(%r)" % (self._arg, self._attributes)
+
     @property
     def connection(self):
         return self._arg.connection
@@ -326,19 +329,16 @@ def __and__(self, restriction):
         """
         When projection has renamed attributes, it must be enclosed in a subquery before restriction
         """
-        if restriction:
-            return Subquery(self) & restriction if self.heading.computed else super().__and__(restriction)
+        return super().__and__(restriction) \
+            if not restriction or not self.heading.computed \
+            else Subquery(self) & restriction
 
 
 class Aggregation(Projection):
     @property
     def _grouped(self):
         return True
 
-    def _repr_helper(self):
-        # TODO: create better repr
-        return "project(%r, %r)" % (self._arg, self._attributes)
-
 
 class Subquery(RelationalOperand):
     """