start sketching ideas for a rewritten unit of work.

the basic idea is to bring topological back down to the raw function,
then the whole UOW constructs itself as very fine grained elements with
full dependencies to each other.  then a straight execute with a straight sort.
the hope is that the mechanism here would be vastly simpler.  while
the presence of a large number of fine-grained records may be expensive
it still is potentially a lot easier to distill into C code, as the
uow's structure now consists of data.

1 files changed, 31 insertions, 644 deletions

diff --git a/lib/sqlalchemy/orm/unitofwork.py b/lib/sqlalchemy/orm/unitofwork.py
index c0a088b01..dc4adff96 100644
--- a/lib/sqlalchemy/orm/unitofwork.py
+++ b/lib/sqlalchemy/orm/unitofwork.py
@@ -23,7 +23,7 @@ changes at once.
 from sqlalchemy import util, log, topological
 from sqlalchemy.orm import attributes, interfaces
 from sqlalchemy.orm import util as mapperutil
-from sqlalchemy.orm.mapper import _state_mapper
+from sqlalchemy.orm.util import _state_mapper
 
 # Load lazily
 object_session = None
@@ -40,7 +40,8 @@ class UOWEventHandler(interfaces.AttributeExtension):
         self.key = key
 
     def append(self, state, item, initiator):
-        # process "save_update" cascade rules for when an instance is appended to the list of another instance
+        # process "save_update" cascade rules for when 
+        # an instance is appended to the list of another instance
         sess = _state_session(state)
         if sess:
             prop = _state_mapper(state).get_property(self.key)
@@ -77,29 +78,23 @@ class UOWTransaction(object):
     """Handles the details of organizing and executing transaction
     tasks during a UnitOfWork object's flush() operation.
 
-    The central operation is to form a graph of nodes represented by the
-    ``UOWTask`` class, which is then traversed by a ``UOWExecutor`` object
-    that issues SQL and instance-synchronizing operations via the related
-    packages.
     """
 
     def __init__(self, session):
         self.session = session
         self.mapper_flush_opts = session._mapper_flush_opts
 
-        # stores tuples of mapper/dependent mapper pairs,
-        # representing a partial ordering fed into topological sort
-        self.dependencies = set()
-
-        # dictionary of mappers to UOWTasks
-        self.tasks = {}
-
         # dictionary used by external actors to store arbitrary state
         # information.
         self.attributes = {}
         
-        self.processors = set()
-    
+        self.recs = []
+        self.states = set()
+        self.dependencies = []
+        
+    def _dependency(self, rec1, rec2):
+        self.dependencies.append((rec1, rec2))
+        
     def get_attribute_history(self, state, key, passive=True):
         hashkey = ("history", state, key)
 
@@ -123,149 +118,32 @@ class UOWTransaction(object):
             return history.as_state()
 
     def register_object(self, state, isdelete=False, 
-                            listonly=False, postupdate=False, post_update_cols=None):
+                            listonly=False, postupdate=False, 
+                            post_update_cols=None):
         
         # if object is not in the overall session, do nothing
         if not self.session._contains_state(state):
             return
-
-        mapper = _state_mapper(state)
-
-        task = self.get_task_by_mapper(mapper)
-        if postupdate:
-            task.append_postupdate(state, post_update_cols)
-        else:
-            task.append(state, listonly=listonly, isdelete=isdelete)
-
-        # ensure the mapper for this object has had its 
-        # DependencyProcessors added.
-        if mapper not in self.processors:
-            mapper._register_processors(self)
-            self.processors.add(mapper)
-
-            if mapper.base_mapper not in self.processors:
-                mapper.base_mapper._register_processors(self)
-                self.processors.add(mapper.base_mapper)
-            
-    def set_row_switch(self, state):
-        """mark a deleted object as a 'row switch'.
-
-        this indicates that an INSERT statement elsewhere corresponds to this DELETE;
-        the INSERT is converted to an UPDATE and the DELETE does not occur.
         
-        """
-        mapper = _state_mapper(state)
-        task = self.get_task_by_mapper(mapper)
-        taskelement = task._objects[state]
-        taskelement.isdelete = "rowswitch"
-    
-    def is_deleted(self, state):
-        """return true if the given state is marked as deleted within this UOWTransaction."""
-
+        if state in self.states:
+            return
+            
         mapper = _state_mapper(state)
-        task = self.get_task_by_mapper(mapper)
-        return task.is_deleted(state)
-
-    def get_task_by_mapper(self, mapper, dontcreate=False):
-        """return UOWTask element corresponding to the given mapper.
-
-        Will create a new UOWTask, including a UOWTask corresponding to the
-        "base" inherited mapper, if needed, unless the dontcreate flag is True.
         
-        """
-        try:
-            return self.tasks[mapper]
-        except KeyError:
-            if dontcreate:
-                return None
-
-            base_mapper = mapper.base_mapper
-            if base_mapper in self.tasks:
-                base_task = self.tasks[base_mapper]
-            else:
-                self.tasks[base_mapper] = base_task = UOWTask(self, base_mapper)
-                base_mapper._register_dependencies(self)
-
-            if mapper not in self.tasks:
-                self.tasks[mapper] = task = UOWTask(self, mapper, base_task=base_task)
-                mapper._register_dependencies(self)
-            else:
-                task = self.tasks[mapper]
-
-            return task
-
-    def register_dependency(self, mapper, dependency):
-        """register a dependency between two mappers.
-
-        Called by ``mapper.PropertyLoader`` to register the objects
-        handled by one mapper being dependent on the objects handled
-        by another.
-
-        """
-        # correct for primary mapper
-        # also convert to the "base mapper", the parentmost task at the top of an inheritance chain
-        # dependency sorting is done via non-inheriting mappers only, dependencies between mappers
-        # in the same inheritance chain is done at the per-object level
-        mapper = mapper.primary_mapper().base_mapper
-        dependency = dependency.primary_mapper().base_mapper
-
-        self.dependencies.add((mapper, dependency))
-
-    def register_processor(self, mapper, processor, mapperfrom):
-        """register a dependency processor, corresponding to 
-        operations which occur between two mappers.
+        self.states.add(state)
         
-        """
-        # correct for primary mapper
-        mapper = mapper.primary_mapper()
-        mapperfrom = mapperfrom.primary_mapper()
-
-        task = self.get_task_by_mapper(mapper)
-        targettask = self.get_task_by_mapper(mapperfrom)
-        up = UOWDependencyProcessor(processor, targettask)
-        task.dependencies.add(up)
-
-    def execute(self):
-        """Execute this UOWTransaction.
-
-        This will organize all collected UOWTasks into a dependency-sorted
-        list which is then traversed using the traversal scheme
-        encoded in the UOWExecutor class.  Operations to mappers and dependency
-        processors are fired off in order to issue SQL to the database and
-        synchronize instance attributes with database values and related
-        foreign key values."""
-
-        # pre-execute dependency processors.  this process may
-        # result in new tasks, objects and/or dependency processors being added,
-        # particularly with 'delete-orphan' cascade rules.
-        # keep running through the full list of tasks until all
-        # objects have been processed.
-        while True:
-            ret = False
-            for task in self.tasks.values():
-                for up in list(task.dependencies):
-                    if up.preexecute(self):
-                        ret = True
-            if not ret:
-                break
-
-        tasks = self._sort_dependencies()
-        if self._should_log_info():
-            self.logger.info("Task dump:\n%s", self._dump(tasks))
-        UOWExecutor().execute(self, tasks)
-        self.logger.info("Execute Complete")
-
-    def _dump(self, tasks):
-        from uowdumper import UOWDumper
-        return UOWDumper.dump(tasks)
-
-    @property
-    def elements(self):
-        """Iterate UOWTaskElements."""
+        self.recs.extend(
+            mapper.get_flush_actions(self, state)
+        )
         
-        for task in self.tasks.itervalues():
-            for elem in task.elements:
-                yield elem
+            
+    def execute(self):
+        # so here, thinking we could figure out a way to get
+        # consecutive, "compatible" records to collapse together,
+        # i.e. a bunch of updates become an executemany(), etc.
+        # even though we usually need individual executes.
+        for rec in topological.sort(self.dependencies, self.recs):
+            rec.execute()
 
     def finalize_flush_changes(self):
         """mark processed objects as clean / deleted after a successful flush().
@@ -280,501 +158,10 @@ class UOWTransaction(object):
             elif not elem.listonly:
                 self.session._register_newly_persistent(elem.state)
 
-    def _sort_dependencies(self):
-        nodes = topological.sort_with_cycles(self.dependencies,
-            [t.mapper for t in self.tasks.itervalues() if t.base_task is t]
-        )
-
-        ret = []
-        for item, cycles in nodes:
-            task = self.get_task_by_mapper(item)
-            if cycles:
-                for t in task._sort_circular_dependencies(
-                                        self, 
-                                        [self.get_task_by_mapper(i) for i in cycles]
-                                        ):
-                    ret.append(t)
-            else:
-                ret.append(task)
-
-        return ret
-
 log.class_logger(UOWTransaction)
 
-class UOWTask(object):
-    """A collection of mapped states corresponding to a particular mapper."""
-    
-    def __init__(self, uowtransaction, mapper, base_task=None):
-        self.uowtransaction = uowtransaction
-
-        # base_task is the UOWTask which represents the "base mapper"
-        # in our mapper's inheritance chain.  if the mapper does not
-        # inherit from any other mapper, the base_task is self.
-        # the _inheriting_tasks dictionary is a dictionary present only
-        # on the "base_task"-holding UOWTask, which maps all mappers within
-        # an inheritance hierarchy to their corresponding UOWTask instances.
-        if base_task is None:
-            self.base_task = self
-            self._inheriting_tasks = {mapper:self}
-        else:
-            self.base_task = base_task
-            base_task._inheriting_tasks[mapper] = self
-
-        # the Mapper which this UOWTask corresponds to
-        self.mapper = mapper
-
-        # mapping of InstanceState -> UOWTaskElement
-        self._objects = {}
-
-        self.dependent_tasks = []
-        self.dependencies = set()
-        self.cyclical_dependencies = set()
-
-    @util.memoized_property
-    def inheriting_mappers(self):
-        return list(self.mapper.polymorphic_iterator())
-
-    @property
-    def polymorphic_tasks(self):
-        """Return an iterator of UOWTask objects corresponding to the
-        inheritance sequence of this UOWTask's mapper.
-
-        e.g. if mapper B and mapper C inherit from mapper A, and
-        mapper D inherits from B:
-
-            mapperA -> mapperB -> mapperD
-                    -> mapperC
-
-        the inheritance sequence starting at mapper A is a depth-first
-        traversal:
-
-            [mapperA, mapperB, mapperD, mapperC]
-
-        this method will therefore return
-
-            [UOWTask(mapperA), UOWTask(mapperB), UOWTask(mapperD),
-             UOWTask(mapperC)]
-
-        The concept of "polymporphic iteration" is adapted into
-        several property-based iterators which return object
-        instances, UOWTaskElements and UOWDependencyProcessors in an
-        order corresponding to this sequence of parent UOWTasks.  This
-        is used to issue operations related to inheritance-chains of
-        mappers in the proper order based on dependencies between
-        those mappers.
-
-        """
-        for mapper in self.inheriting_mappers:
-            t = self.base_task._inheriting_tasks.get(mapper, None)
-            if t is not None:
-                yield t
-
-    def is_empty(self):
-        """return True if this UOWTask is 'empty', meaning it has no child items.
-
-        used only for debugging output.
-        """
-
-        return not self._objects and not self.dependencies
-
-    def append(self, state, listonly=False, isdelete=False):
-        if state not in self._objects:
-            self._objects[state] = rec = UOWTaskElement(state)
-        else:
-            rec = self._objects[state]
-
-        rec.update(listonly, isdelete)
-
-    def append_postupdate(self, state, post_update_cols):
-        """issue a 'post update' UPDATE statement via this object's mapper immediately.
-
-        this operation is used only with relationships that specify the `post_update=True`
-        flag.
-        """
-
-        # postupdates are UPDATED immeditely (for now)
-        # convert post_update_cols list to a Set so that __hash__() is used to compare columns
-        # instead of __eq__()
-        self.mapper._save_obj([state], self.uowtransaction, postupdate=True, post_update_cols=set(post_update_cols))
-
-    def __contains__(self, state):
-        """return True if the given object is contained within this UOWTask or inheriting tasks."""
-
-        for task in self.polymorphic_tasks:
-            if state in task._objects:
-                return True
-        else:
-            return False
-
-    def is_deleted(self, state):
-        """return True if the given object is marked as to be deleted within this UOWTask."""
-
-        try:
-            return self._objects[state].isdelete
-        except KeyError:
-            return False
-
-    def _polymorphic_collection(fn):
-        """return a property that will adapt the collection returned by the
-        given callable into a polymorphic traversal."""
-
-        @property
-        def collection(self):
-            for task in self.polymorphic_tasks:
-                for rec in fn(task):
-                    yield rec
-        return collection
-
-    def _polymorphic_collection_filtered(fn):
-
-        def collection(self, mappers):
-            for task in self.polymorphic_tasks:
-                if task.mapper in mappers:
-                    for rec in fn(task):
-                        yield rec
-        return collection
-
-    @property
-    def elements(self):
-        return self._objects.values()
-
-    @_polymorphic_collection
-    def polymorphic_elements(self):
-        return self.elements
-
-    @_polymorphic_collection_filtered
-    def filter_polymorphic_elements(self):
-        return self.elements
-
-    @property
-    def polymorphic_tosave_elements(self):
-        return [rec for rec in self.polymorphic_elements if not rec.isdelete]
-
-    @property
-    def polymorphic_todelete_elements(self):
-        return [rec for rec in self.polymorphic_elements if rec.isdelete]
-
-    @property
-    def polymorphic_tosave_objects(self):
-        return [
-            rec.state for rec in self.polymorphic_elements
-            if rec.state is not None and not rec.listonly and rec.isdelete is False
-        ]
-
-    @property
-    def polymorphic_todelete_objects(self):
-        return [
-            rec.state for rec in self.polymorphic_elements
-            if rec.state is not None and not rec.listonly and rec.isdelete is True
-        ]
-
-    @_polymorphic_collection
-    def polymorphic_dependencies(self):
-        return self.dependencies
-
-    @_polymorphic_collection
-    def polymorphic_cyclical_dependencies(self):
-        return self.cyclical_dependencies
-
-    def _sort_circular_dependencies(self, trans, cycles):
-        """Topologically sort individual entities with row-level dependencies.
-        
-        Builds a modified UOWTask structure, and is invoked when the
-        per-mapper topological structure is found to have cycles.
-        
-        """
-        dependencies = {}
-        def set_processor_for_state(state, depprocessor, target_state, isdelete):
-            if state not in dependencies:
-                dependencies[state] = {}
-            tasks = dependencies[state]
-            if depprocessor not in tasks:
-                tasks[depprocessor] = UOWDependencyProcessor(
-                                            depprocessor.processor, 
-                                            UOWTask(self.uowtransaction, depprocessor.targettask.mapper)
-                                      )
-            tasks[depprocessor].targettask.append(target_state, isdelete=isdelete)
-            
-        cycles = set(cycles)
-        def dependency_in_cycles(dep):
-            proctask = trans.get_task_by_mapper(dep.processor.mapper.base_mapper, True)
-            targettask = trans.get_task_by_mapper(dep.targettask.mapper.base_mapper, True)
-            return targettask in cycles and (proctask is not None and proctask in cycles)
-
-        deps_by_targettask = {}
-        extradeplist = []
-        for task in cycles:
-            for dep in task.polymorphic_dependencies:
-                if not dependency_in_cycles(dep):
-                    extradeplist.append(dep)
-                for t in dep.targettask.polymorphic_tasks:
-                    l = deps_by_targettask.setdefault(t, [])
-                    l.append(dep)
-
-        object_to_original_task = {}
-        tuples = []
-
-        for task in cycles:
-            for subtask in task.polymorphic_tasks:
-                for taskelement in subtask.elements:
-                    state = taskelement.state
-                    object_to_original_task[state] = subtask
-                    if subtask not in deps_by_targettask:
-                        continue
-                    for dep in deps_by_targettask[subtask]:
-                        if not dep.processor.has_dependencies or not dependency_in_cycles(dep):
-                            continue
-                        (processor, targettask) = (dep.processor, dep.targettask)
-                        isdelete = taskelement.isdelete
-
-                        # list of dependent objects from this object
-                        (added, unchanged, deleted) = dep.get_object_dependencies(state, trans, passive=True)
-                        if not added and not unchanged and not deleted:
-                            continue
-
-                        # the task corresponding to saving/deleting of those dependent objects
-                        childtask = trans.get_task_by_mapper(processor.mapper)
-
-                        childlist = added + unchanged + deleted
-
-                        for o in childlist:
-                            if o is None:
-                                continue
-
-                            if o not in childtask:
-                                childtask.append(o, listonly=True)
-                                object_to_original_task[o] = childtask
-
-                            whosdep = dep.whose_dependent_on_who(state, o)
-                            if whosdep is not None:
-                                tuples.append(whosdep)
-
-                                if whosdep[0] is state:
-                                    set_processor_for_state(whosdep[0], dep, whosdep[0], isdelete=isdelete)
-                                else:
-                                    set_processor_for_state(whosdep[0], dep, whosdep[1], isdelete=isdelete)
-                            else:
-                                # TODO: no test coverage here
-                                set_processor_for_state(state, dep, state, isdelete=isdelete)
-
-        t = UOWTask(self.uowtransaction, self.mapper)
-        t.dependencies.update(extradeplist)
-
-        used_tasks = set()
-
-        # rationale for "tree" sort as opposed to a straight
-        # dependency - keep non-dependent objects
-        # grouped together, so that insert ordering as determined
-        # by session.add() is maintained.
-        # An alternative might be to represent the "insert order"
-        # as part of the topological sort itself, which would
-        # eliminate the need for this step (but may make the original
-        # topological sort more expensive)
-        head = topological.sort_as_tree(tuples, object_to_original_task.iterkeys())
-        if head is not None:
-            original_to_tasks = {}
-            stack = [(head, t)]
-            while stack:
-                ((state, cycles, children), parenttask) = stack.pop()
-
-                originating_task = object_to_original_task[state]
-                used_tasks.add(originating_task)
-
-                if (parenttask, originating_task) not in original_to_tasks:
-                    task = UOWTask(self.uowtransaction, originating_task.mapper)
-                    original_to_tasks[(parenttask, originating_task)] = task
-                    parenttask.dependent_tasks.append(task)
-                else:
-                    task = original_to_tasks[(parenttask, originating_task)]
-
-                task.append(state, originating_task._objects[state].listonly, isdelete=originating_task._objects[state].isdelete)
-
-                if state in dependencies:
-                    task.cyclical_dependencies.update(dependencies[state].itervalues())
-
-                stack += [(n, task) for n in children]
-
-        ret = [t]
-
-        # add tasks that were in the cycle, but didnt get assembled
-        # into the cyclical tree, to the start of the list
-        for t2 in cycles:
-            if t2 not in used_tasks and t2 is not self:
-                localtask = UOWTask(self.uowtransaction, t2.mapper)
-                for state in t2.elements:
-                    localtask.append(state, t2.listonly, isdelete=t2._objects[state].isdelete)
-                for dep in t2.dependencies:
-                    localtask.dependencies.add(dep)
-                ret.insert(0, localtask)
-
-        return ret
-
-    def __repr__(self):
-        return ("UOWTask(%s) Mapper: '%r'" % (hex(id(self)), self.mapper))
-
-class UOWTaskElement(object):
-    """Corresponds to a single InstanceState to be saved, deleted,
-    or otherwise marked as having dependencies.  A collection of
-    UOWTaskElements are held by a UOWTask.
-
-    """
-    def __init__(self, state):
-        self.state = state
-        self.listonly = True
-        self.isdelete = False
-        self.preprocessed = set()
-
-    def update(self, listonly, isdelete):
-        if not listonly and self.listonly:
-            self.listonly = False
-            self.preprocessed.clear()
-        if isdelete and not self.isdelete:
-            self.isdelete = True
-            self.preprocessed.clear()
-
-    def __repr__(self):
-        return "UOWTaskElement/%d: %s/%d %s" % (
-            id(self), 
-            self.state.class_.__name__, 
-            id(self.state.obj()), 
-            (self.listonly and 'listonly' or (self.isdelete and 'delete' or 'save')) 
-        )
-
-class UOWDependencyProcessor(object):
-    """In between the saving and deleting of objects, process
-    dependent data, such as filling in a foreign key on a child item
-    from a new primary key, or deleting association rows before a
-    delete.  This object acts as a proxy to a DependencyProcessor.
-
-    """
-    def __init__(self, processor, targettask):
-        self.processor = processor
-        self.targettask = targettask
-        prop = processor.prop
-        
-        # define a set of mappers which
-        # will filter the lists of entities
-        # this UOWDP processes.  this allows
-        # MapperProperties to be overridden
-        # at least for concrete mappers.
-        self._mappers = set([
-            m
-            for m in self.processor.parent.polymorphic_iterator()
-            if m._props[prop.key] is prop
-        ]).union(self.processor.mapper.polymorphic_iterator())
-            
-    def __repr__(self):
-        return "UOWDependencyProcessor(%s, %s)" % (str(self.processor), str(self.targettask))
-
-    def __eq__(self, other):
-        return other.processor is self.processor and other.targettask is self.targettask
-
-    def __hash__(self):
-        return hash((self.processor, self.targettask))
-
-    def preexecute(self, trans):
-        """preprocess all objects contained within this ``UOWDependencyProcessor``s target task.
-
-        This may locate additional objects which should be part of the
-        transaction, such as those affected deletes, orphans to be
-        deleted, etc.
-
-        Once an object is preprocessed, its ``UOWTaskElement`` is marked as processed.  If subsequent
-        changes occur to the ``UOWTaskElement``, its processed flag is reset, and will require processing
-        again.
-
-        Return True if any objects were preprocessed, or False if no
-        objects were preprocessed.  If True is returned, the parent ``UOWTransaction`` will
-        ultimately call ``preexecute()`` again on all processors until no new objects are processed.
-        """
-
-        def getobj(elem):
-            elem.preprocessed.add(self)
-            return elem.state
-
-        ret = False
-        elements = [getobj(elem) for elem in 
-                        self.targettask.filter_polymorphic_elements(self._mappers)
-                        if self not in elem.preprocessed and not elem.isdelete]
-        if elements:
-            ret = True
-            self.processor.preprocess_dependencies(self.targettask, elements, trans, delete=False)
-
-        elements = [getobj(elem) for elem in 
-                        self.targettask.filter_polymorphic_elements(self._mappers)
-                        if self not in elem.preprocessed and elem.isdelete]
-        if elements:
-            ret = True
-            self.processor.preprocess_dependencies(self.targettask, elements, trans, delete=True)
-        return ret
-
-    def execute(self, trans, delete):
-        """process all objects contained within this ``UOWDependencyProcessor``s target task."""
-
-
-        elements = [e for e in 
-                    self.targettask.filter_polymorphic_elements(self._mappers) 
-                    if bool(e.isdelete)==delete]
-
-        self.processor.process_dependencies(
-            self.targettask, 
-            [elem.state for elem in elements], 
-            trans, 
-            delete=delete)
-
-    def get_object_dependencies(self, state, trans, passive):
-        return trans.get_attribute_history(state, self.processor.key, passive=passive)
-
-    def whose_dependent_on_who(self, state1, state2):
-        """establish which object is operationally dependent amongst a parent/child
-        using the semantics stated by the dependency processor.
-
-        This method is used to establish a partial ordering (set of dependency tuples)
-        when toplogically sorting on a per-instance basis.
-
-        """
-        return self.processor.whose_dependent_on_who(state1, state2)
-
-class UOWExecutor(object):
-    """Encapsulates the execution traversal of a UOWTransaction structure."""
-
-    def execute(self, trans, tasks, isdelete=None):
-        if isdelete is not True:
-            for task in tasks:
-                self.execute_save_steps(trans, task)
-        if isdelete is not False:
-            for task in reversed(tasks):
-                self.execute_delete_steps(trans, task)
-
-    def save_objects(self, trans, task):
-        task.mapper._save_obj(task.polymorphic_tosave_objects, trans)
-
-    def delete_objects(self, trans, task):
-        task.mapper._delete_obj(task.polymorphic_todelete_objects, trans)
-
-    def execute_dependency(self, trans, dep, isdelete):
-        dep.execute(trans, isdelete)
-
-    def execute_save_steps(self, trans, task):
-        self.save_objects(trans, task)
-        for dep in task.polymorphic_cyclical_dependencies:
-            self.execute_dependency(trans, dep, False)
-        for dep in task.polymorphic_cyclical_dependencies:
-            self.execute_dependency(trans, dep, True)
-        self.execute_cyclical_dependencies(trans, task, False)
-        self.execute_dependencies(trans, task)
-
-    def execute_delete_steps(self, trans, task):
-        self.execute_cyclical_dependencies(trans, task, True)
-        self.delete_objects(trans, task)
-
-    def execute_dependencies(self, trans, task):
-        polymorphic_dependencies = list(task.polymorphic_dependencies)
-        for dep in polymorphic_dependencies:
-            self.execute_dependency(trans, dep, False)
-        for dep in reversed(polymorphic_dependencies):
-            self.execute_dependency(trans, dep, True)
+# TODO: don't know what these should be.
+# its very hard not to use subclasses to define behavior here.
+class Rec(object):
+    pass
 
-    def execute_cyclical_dependencies(self, trans, task, isdelete):
-        for t in task.dependent_tasks:
-            self.execute(trans, [t], isdelete)