marking an object "read-only" / recursive expunge?

[Jonathan Vanasco]

I'm updating our "visual preview" tool for edits, and ran into an issue.  

In order to best mimic the production view, I can't simply "clone" the objects any longer (they have way too many attributes and relationships) and must apply edits onto the real object.  

I'd like to ensure that changes can't persist, so the easiest way to mark the object "read only" was to expunge it from the session.  Perfect.

The problem I've run into, is that `expunge()` only applies to the actual object -- it doesn't apply to any of the loaded (lazy/eager/etc) relationships.  

Has anyone figured out way to do a recursive expunge?  I don't want to alter the cascades on the relationship, I just have one (or more) context(s) where I need to disassociate an object and any loaded children from the session.

[Mike Bayer]

there's an "expunge" cascade you can set on relationship:

http://docs.sqlalchemy.org/en/rel_1_0/orm/cascades.html#expunge

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[Jonathan Vanasco]

editing the cascade isn't an option.  

for now this seems to work, though it's ugly.

        def recursive_expunge(obj, dbSession):

            def _recursive_expunge(_obj):

                if hasattr(_obj, '__mapper__'):

                    for rel in obj.__mapper__.relationships:

                        try:

                            dbSession.expunge(rel)

                        except sqlalchemy.orm.exc.UnmappedInstanceError:

                            pass

            _recursive_expunge(obj)

        recursive_expunge(postingObject, self.request.dbSession.writer)

[Mike Bayer]

On 7/17/15 2:32 PM, Jonathan Vanasco wrote:

editing the cascade isn't an option. 

well then yeah you need to do your own thing :)

i'd use inspect(obj) to get the mapper.    but also you might want to use cascade_iterator: http://docs.sqlalchemy.org/en/rel_1_0/orm/mapping_api.html?highlight=cascade_iterator#sqlalchemy.orm.mapper.Mapper.cascade_iterator

[Jonathan Vanasco]

On Friday, July 17, 2015 at 2:46:42 PM UTC-4, Michael Bayer wrote:

well then yeah you need to do your own thing :)

i foolishly thought this was something others may have experienced ;)

 

i'd use inspect(obj) to get the mapper.    but also you might want to use cascade_iterator: http://docs.sqlalchemy.org/en/rel_1_0/orm/mapping_api.html?highlight=cascade_iterator#sqlalchemy.orm.mapper.Mapper.cascade_iterator

 

i'll look into the cascade_iterator.  I keep forgetting that inspect is not just for debugging.

 

[Jonathan Vanasco]

So my code above is just completely wrong.  

This code actually does what one expects:

    def recursive_expunge(obj, dbSession):

        def _recursive_expunge(_obj):

            _instance_state = sqlalchemy.inspection.inspect(_obj)

            _mapper = _instance_state.mapper

            try:

                dbSession.expunge(_obj)

                # print "expunge | %s" % _obj

            except sqlalchemy.orm.exc.UnmappedInstanceError:

                # print "sqlalchemy.orm.exc.UnmappedInstanceError | %s" % _obj

                pass

            except sqlalchemy.exc.InvalidRequestError:

                # print "sqlalchemy.exc.UnmappedInstanceError | %s" % _obj

                pass

            if _mapper:

                # _unloaded = [(_name, _rel) for (_name, _rel) in _mapper.relationships.items() if _name in _instance_state.unloaded]

                _loaded_rels = [i for i in _mapper.relationships.items() if i[0] not in _instance_state.unloaded]

                for (_name, _rel) in _loaded_rels:

                    _loaded_rel_data = getattr(_obj, _name)

                    if _loaded_rel_data:

                        if not _rel.uselist:

                            _recursive_expunge(_loaded_rel_data)

                        else:

                            for _i in _loaded_rel_data:

                                _recursive_expunge(_i)

        _recursive_expunge(obj)