On 6/29/15 5:37 AM, Adrian wrote:
I tried this code:
@listens_for(AttachmentFolder.all_attachments, 'append')
def _attachment_added(target, value, *unused):
target.modified_dt = now_utc()
However AttachmentFolder.all_attachments is a backref so it doesn't
exist at import time (I usually
register listeners right after the definition of the model class). So
I tried using the mapper_configured
event, but backrefs still don't exist at that point.
Besides flipping the relationship/backref around (which would work
only because I don't have
any listeners on the relationship itself yet), is there any clean way
to bind an event listener
to a backref?
During mapper_configured(), backrefs which *originate* from that mapper
should have been built up, however the receiving mapper may have already
been invoked on mapper_configured() before this other mapper adds the
backref relationship.
For this reason the SQLAlchemy documentation (outside of the tutorial)
recommends to forego the use of backref() and use two relationship()
objects instead with back_populates; this is clearer and simpler.
Another event you can use is the after_configured() event which fires
once *all* mappers are set up, that would work also.
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