Re: [sqlalchemy] How to do a revision table or How to get a 1:1 and 1:n relationship between the same tables to work properly
I hadn't seen that part of the documentation - doing it that way works fine now! I ended up using a signal to update `revisions` automatically when setting `current_revision`: https://github.com/ThiefMaster/indico/blob/f300c3b9dc8d499b4d745dee74edceff53e7ffb4/indico/modules/events/notes/models/notes.py#L159-L164 Is there any better way to do this or is that the way to go? I'd definitely advise doing it that way, that's the supported way to do a favorite id approach and is more relationally correct (e.g. not possible to have multiple favorites).It seems like you read the docs at http://docs.sqlalchemy.org/en/rel_1_0/orm/relationship_persistence.html#rows-that-point-to-themselves-mutually-dependent-rows, so I'd give that a revisit and feel free to share the errors from that case. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
Re: [sqlalchemy] How to do a revision table or How to get a 1:1 and 1:n relationship between the same tables to work properly
have you taken a look at this approach? https://bitbucket.org/zzzeek/sqlalchemy/src/4a25c10e27147917e93e6893df13b2b55673e0a7/examples/versioned_history/?at=master chers, richard. On 06/18/2015 08:44 AM, Adrian wrote: I hadn't seen that part of the documentation - doing it that way works fine now! I ended up using a signal to update `revisions` automatically when setting `current_revision`: https://github.com/ThiefMaster/indico/blob/f300c3b9dc8d499b4d745dee74edceff53e7ffb4/indico/modules/events/notes/models/notes.py#L159-L164 Is there any better way to do this or is that the way to go? I'd definitely advise doing it that way, that's the supported way to do a favorite id approach and is more relationally correct (e.g. not possible to have multiple favorites).It seems like you read the docs at http://docs.sqlalchemy.org/en/rel_1_0/orm/relationship_persistence.html#rows-that-point-to-themselves-mutually-dependent-rows http://docs.sqlalchemy.org/en/rel_1_0/orm/relationship_persistence.html#rows-that-point-to-themselves-mutually-dependent-rows, so I'd give that a revisit and feel free to share the errors from that case. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com mailto:sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com mailto:sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout. attachment: richard.vcf
Re: [sqlalchemy] How to do a revision table or How to get a 1:1 and 1:n relationship between the same tables to work properly
On 6/17/15 12:00 PM, Adrian wrote:
I'm trying to store old versions of (some of) the data in one of my
tables.
To do so, I'm thinking about models like this (not including anything
not relevant to the case):
class EventNote(db.Model):
id = db.Column(db.Integer, primary_key=True)
latest_revision = db.relationship(
'EventNoteRevision',
lazy=False,
uselist=False,
primaryjoin=lambda: (EventNote.id ==
EventNoteRevision.note_id) EventNoteRevision.is_latest,
back_populates='note'
)
revisions = db.relationship(
'EventNoteRevision',
lazy=True,
cascade='all, delete-orphan',
primaryjoin=lambda: EventNote.id == EventNoteRevision.note_id,
order_by=lambda: EventNoteRevision.created_dt.desc(),
back_populates='note'
)
class EventNoteRevision(db.Model):
id = db.Column(db.Integer, primary_key=True)
note_id = db.Column(db.Integer, db.ForeignKey('events.notes.id'),
nullable=False, index=True)
is_latest = db.Column(db.Boolean, nullable=False, default=False)
# ...and some columns for the actual data of that revision
note = db.relationship(
'EventNote',
lazy=False,
back_populates='revisions'
)
However, it always breaks somewhere (I was trying around with some
variations in the relationship configurations)...
These are the problems I've encountered so far:
- A newly created revision assigned to `latest_revision` is flushed
with a null `note_id
- Assigning a new revision to `latest_revision` (i.e. with another
revision already existing) results in the old one being DELETEd or its
note_id being NULLed out (neither should happen)
Well the concept of back_populates pointing in three directions like
that is not how it was intended to be used. back_populates is intended
to point two relationships to each other mutually. I'm not sure why
these effects are happening but it probably has something to do with
that. I could dig into what's going on and I may do so, but I'm sure
whatever I see will come to the same immediate solution anyway.
If keeping this model, I would keep EventNote.revisions and
EventNoteRevision.note as the two relationships here with a traditional
back_populates between them. The latest_revision relationship here at
most should just be a viewonly=True. reviisions/note should be used as
the persistence channel exclusively.
I could really use some help on how to do this properly. The model
posted above can be changed in any way. For example, I wouldn't mind
having a `latest_revision_id` column in `EventNote`,
but when I tried that (including `use_alter` and `post_update`) I also
ended up with tons of different errors, including some that showed up
every other time I started my application (seems like
something doesn't happen in a deterministic order during mapper
configuration).
I'd definitely advise doing it that way, that's the supported way to do
a favorite id approach and is more relationally correct (e.g. not
possible to have multiple favorites).It seems like you read the
docs at
http://docs.sqlalchemy.org/en/rel_1_0/orm/relationship_persistence.html#rows-that-point-to-themselves-mutually-dependent-rows,
so I'd give that a revisit and feel free to share the errors from that case.
--
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[sqlalchemy] How to do a revision table or How to get a 1:1 and 1:n relationship between the same tables to work properly
I'm trying to store old versions of (some of) the data in one of my tables.
To do so, I'm thinking about models like this (not including anything not
relevant to the case):
class EventNote(db.Model):
id = db.Column(db.Integer, primary_key=True)
latest_revision = db.relationship(
'EventNoteRevision',
lazy=False,
uselist=False,
primaryjoin=lambda: (EventNote.id == EventNoteRevision.note_id)
EventNoteRevision.is_latest,
back_populates='note'
)
revisions = db.relationship(
'EventNoteRevision',
lazy=True,
cascade='all, delete-orphan',
primaryjoin=lambda: EventNote.id == EventNoteRevision.note_id,
order_by=lambda: EventNoteRevision.created_dt.desc(),
back_populates='note'
)
class EventNoteRevision(db.Model):
id = db.Column(db.Integer, primary_key=True)
note_id = db.Column(db.Integer, db.ForeignKey('events.notes.id'),
nullable=False, index=True)
is_latest = db.Column(db.Boolean, nullable=False, default=False)
# ...and some columns for the actual data of that revision
note = db.relationship(
'EventNote',
lazy=False,
back_populates='revisions'
)
However, it always breaks somewhere (I was trying around with some
variations in the relationship configurations)...
These are the problems I've encountered so far:
- A newly created revision assigned to `latest_revision` is flushed with a
null `note_id`
- Assigning a new revision to `latest_revision` (i.e. with another revision
already existing) results in the old one being DELETEd or its note_id being
NULLed out (neither should happen)
I could really use some help on how to do this properly. The model posted
above can be changed in any way. For example, I wouldn't mind having a
`latest_revision_id` column in `EventNote`,
but when I tried that (including `use_alter` and `post_update`) I also
ended up with tons of different errors, including some that showed up every
other time I started my application (seems like
something doesn't happen in a deterministic order during mapper
configuration).
One option to avoid all the problems could be using the revision table only
for OLD data, i.e. keeping all the latest data inside `EventNote` and only
adding a new revision when something changes.
That way I would avoid having two relationships and all the problems would
go away. I know at least one big site doing it like this (Stack Overflow),
so maybe it's not the worst option... even though
they probably had other reasons to do it like this since they aren't using
SQLAlchemy. But after having spent half the afternoon trying to get the
two-relationship solution working I'm really tempted
to do it like this... Especially since I wouldn't have to worry about
allowing only one `is_latest` revision per `note_id` (easy with a
conditional unique index, but needs extra code to mark the old ones
as not being the latest one anymore)
--
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