I didn't mean to confuse this question by showing both formats of the many-to-many relationship (using secondary and not); I am aware that using both can lead to problems / inconsistencies.
I just wanted to show that I had both options available at my disposal. Is there anyway to use the secondary relationship (rather than the association one) with some combination of cascading options to get what I want where I can create and use a Geography knowing only its pk without the ORM trying to then save it to the DB? On Thursday, August 23, 2018 at 1:02:40 PM UTC-4, Mike Bayer wrote: > > On Wed, Aug 22, 2018 at 5:41 PM, Alex Rothberg <agrot...@gmail.com > <javascript:>> wrote: > > I am using an association model / table to represent a many to many > > relationship: > > > > class Geography(db.Model): > > > > id = > > ... > > > > class Fund(db.Model): > > id = > > ... > > geography_associations = db.relationship( > > lambda: FundGeographyAssociation, > > back_populates="fund", > > cascade='save-update, merge, delete, delete-orphan' > > ) > > > > geographies = db.relationship( > > Geography, > > backref="fund", > > secondary=lambda: FundGeographyAssociation.__table__, > > ) > > > > class FundGeographyAssociation(db.Model): > > fund_id = db.Column( > > UUID, db.ForeignKey(Fund.id), primary_key=True, > > ) > > geography_id = db.Column( > > UUID, db.ForeignKey(Geography.id), primary_key=True, > > ) > > > > fund = db.relationship(Fund, > back_populates='geography_associations') > > > > > > and then am attempting to update the list of geographies for a Fund > using: > > fund.geographies = [????] > > > > > > my issue is what to put in ??? when I only have the pk of the geography > > model. > > it is not a recommended pattern to re-purpose a mapped association > class as a "secondary" elsewhere. The ORM does not know that > Fund.geography_associations and Fund.geographies refer to the same > table and mutations to each of these independently will conflict (see > > http://docs.sqlalchemy.org/en/latest/orm/basic_relationships.html#association-object) > > > . The usual pattern is to use an association proxy for > Fund.geographies (see > > http://docs.sqlalchemy.org/en/latest/orm/extensions/associationproxy.html#simplifying-association-objects). > > > > If you want to add a row having only the id of Geography, the most > straightforward approach is to append the association object directly: > > fund.geography_associations = [FundGeoAssoc(geo_id=1)] > > > > > > this works: Geography.query.get(id) however this does not: > Geography(id=id) > > as the latter tries to create a new Geography object leading to > conflicts. > > The former seems "silly" as it requires an extra query to db to load the > > object even though all i need is the geography id to create the > association > > object. I tried variation of session.merge with load=False however that > > doesn't work as the object is transient. > > > > -- > > SQLAlchemy - > > The Python SQL Toolkit and Object Relational Mapper > > > > http://www.sqlalchemy.org/ > > > > To post example code, please provide an MCVE: Minimal, Complete, and > > Verifiable Example. See http://stackoverflow.com/help/mcve for a full > > description. > > --- > > 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+...@googlegroups.com <javascript:>. > > To post to this group, send email to sqlal...@googlegroups.com > <javascript:>. > > Visit this group at https://groups.google.com/group/sqlalchemy. > > For more options, visit https://groups.google.com/d/optout. > -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- 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 https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
