path: root/lib/sqlalchemy/orm/unitofwork.py

# orm/unitofwork.py
# Copyright (C) 2005, 2006, 2007, 2008, 2009 Michael Bayer mike_mp@zzzcomputing.com
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""The internals for the Unit Of Work system.

Includes hooks into the attributes package enabling the routing of
change events to Unit Of Work objects, as well as the flush()
mechanism which creates a dependency structure that executes change
operations.

A Unit of Work is essentially a system of maintaining a graph of
in-memory objects and their modified state.  Objects are maintained as
unique against their primary key identity using an *identity map*
pattern.  The Unit of Work then maintains lists of objects that are
new, dirty, or deleted and provides the capability to flush all those
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

# Load lazily
object_session = None
_state_session = None

class UOWEventHandler(interfaces.AttributeExtension):
    """An event handler added to all relation attributes which handles
    session cascade operations.
    """

    def __init__(self, key):
        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
        sess = _state_session(state)
        if sess:
            prop = _state_mapper(state).get_property(self.key)
            if prop.cascade.save_update and item not in sess:
                sess.add(item)
        return item
        
    def remove(self, state, item, initiator):
        sess = _state_session(state)
        if sess:
            prop = _state_mapper(state).get_property(self.key)
            # expunge pending orphans
            if prop.cascade.delete_orphan and \
                item in sess.new and \
                prop.mapper._is_orphan(attributes.instance_state(item)):
                    sess.expunge(item)

    def set(self, state, newvalue, oldvalue, initiator):
        # process "save_update" cascade rules for when an instance is attached to another instance
        if oldvalue is newvalue:
            return newvalue
        sess = _state_session(state)
        if sess:
            prop = _state_mapper(state).get_property(self.key)
            if newvalue is not None and prop.cascade.save_update and newvalue not in sess:
                sess.add(newvalue)
            if prop.cascade.delete_orphan and oldvalue in sess.new and \
                prop.mapper._is_orphan(attributes.instance_state(oldvalue)):
                sess.expunge(oldvalue)
        return newvalue


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 = {}
        
    def get_attribute_history(self, state, key, passive=True):
        hashkey = ("history", state, key)

        # cache the objects, not the states; the strong reference here
        # prevents newly loaded objects from being dereferenced during the
        # flush process
        if hashkey in self.attributes:
            (history, cached_passive) = self.attributes[hashkey]
            # if the cached lookup was "passive" and now we want non-passive, do a non-passive
            # lookup and re-cache
            if cached_passive and not passive:
                history = attributes.get_history(state, key, passive=False)
                self.attributes[hashkey] = (history, passive)
        else:
            history = attributes.get_history(state, key, passive=passive)
            self.attributes[hashkey] = (history, passive)

        if not history or not state.get_impl(key).uses_objects:
            return history
        else:
            return history.as_state()

    def register_object(self, state, isdelete=False, 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):
            if self._should_log_debug:
                self.logger.debug("object %s not part of session, not registering for flush" % (mapperutil.state_str(state)))
            return

        if self._should_log_debug:
            self.logger.debug("register object for flush: %s isdelete=%s listonly=%s postupdate=%s" % (mapperutil.state_str(state), isdelete, listonly, postupdate))

        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)

    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."""

        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 dependencies between
        the two given mappers.

        """
        # 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" + self._dump(tasks))
        UOWExecutor().execute(self, tasks)
        if self._should_log_info:
            self.logger.info("Execute Complete")

    def _dump(self, tasks):
        from uowdumper import UOWDumper
        return UOWDumper.dump(tasks)

    @property
    def elements(self):
        """Iterate UOWTaskElements."""
        
        for task in self.tasks.itervalues():
            for elem in task.elements:
                yield elem

    def finalize_flush_changes(self):
        """mark processed objects as clean / deleted after a successful flush().

        this method is called within the flush() method after the
        execute() method has succeeded and the transaction has been committed.
        """

        for elem in self.elements:
            if elem.isdelete:
                self.session._remove_newly_deleted(elem.state)
            else:
                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)

        if self._should_log_debug:
            self.logger.debug("Dependent tuples:\n" + "\n".join(
                    "(%s->%s)" % (d[0].class_.__name__, d[1].class_.__name__)
                    for d in self.dependencies))
            self.logger.debug("Dependency sort:\n"+ str(ret))
        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 relations 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

    @property
    def elements(self):
        return self._objects.values()

    @_polymorphic_collection
    def 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 dep.processor.no_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

    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.polymorphic_tosave_elements if self not in elem.preprocessed]
        if elements:
            ret = True
            self.processor.preprocess_dependencies(self.targettask, elements, trans, delete=False)

        elements = [getobj(elem) for elem in self.targettask.polymorphic_todelete_elements if self not in elem.preprocessed]
        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."""

        if delete:
            elements = self.targettask.polymorphic_todelete_elements
        else:
            elements = self.targettask.polymorphic_tosave_elements

        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)
        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)

    def execute_cyclical_dependencies(self, trans, task, isdelete):
        for dep in task.polymorphic_cyclical_dependencies:
            self.execute_dependency(trans, dep, isdelete)
        for t in task.dependent_tasks:
            self.execute(trans, [t], isdelete)