On Wed, Mar 18, 2020, at 11:42 AM, Mike Bayer wrote: > > > On Wed, Mar 18, 2020, at 11:22 AM, Tony Hignett wrote: >> Hi, >> >> I'm trying to upgrade from 1.2.2 to 1.3.15 and a number of our relations >> have started generating these warnings: >> ``` >> SAWarning: Setting backref / back_populates on relationship <child.parent> >> to refer to viewonly relationship <parent.children> will be deprecated in >> SQLAlchemy 1.4, and will be disallowed in a future release. viewonly >> relationships should not be mutated (this warning may be suppressed after 10 >> occurrences) >> (self, other), >> ``` >> >> I've read some of the related issues, e.g. >> https://github.com/sqlalchemy/sqlalchemy/issues/5149, >> https://github.com/sqlalchemy/sqlalchemy/issues/ >> <https://github.com/sqlalchemy/sqlalchemy/issues/5149>4993, but I don't >> understand how backref comes into it. We don't want to mutate anything along >> the backref. >> >> Is there a way of expressing a two-way read-only relation? > > you should remove the backref. have the "viewonly" relationship stand alone > by itself.
also if you want 'children1' to also be a viewonly relationship, set that up separately. > > >> >> The code looks like >> ``` >> class Parent(Base): >> pass >> >> class Child1(Base): >> >> @declared_attr >> def parent(cls): >> return orm.relationship( >> Parent, >> ..., >> viewonly=True, >> backref="children1" >> ) >> >> class Child2(Base): >> [etc] >> ```` >> >> -- >> 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 view this discussion on the web visit >> https://groups.google.com/d/msgid/sqlalchemy/660cedf0-7066-42fe-93bc-d6e4d223b05c%40googlegroups.com >> >> <https://groups.google.com/d/msgid/sqlalchemy/660cedf0-7066-42fe-93bc-d6e4d223b05c%40googlegroups.com?utm_medium=email&utm_source=footer>. > > > -- > 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 view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy/40c0410d-0233-4abc-aae7-bfe728495647%40www.fastmail.com > > <https://groups.google.com/d/msgid/sqlalchemy/40c0410d-0233-4abc-aae7-bfe728495647%40www.fastmail.com?utm_medium=email&utm_source=footer>. -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/sqlalchemy/9844a940-fa9c-4b15-b031-7f507f299af3%40www.fastmail.com.
