Thank you, I am reading Architecture Patterns with Python <https://www.cosmicpython.com/book/chapter_02_repository.html> and trying to find a way to refactor our code to become maintainable. However I noticed that even with mapped dataclass there are problems like the one mentioned here <https://github.com/cosmicpython/code/issues/17> and proposed solution is to use *InstrumentationManager* you just mentioned, but even with this approach resulting dataclass will be "linked" to ORM object via internal attributes, defeating the purpose of Registry pattern proposed in the book.
Would it be OK to simply use dict objects as adapter between dataclass and ORM? Kindest regards On Monday, September 20, 2021 at 4:04:05 PM UTC+2 Mike Bayer wrote: > > > On Mon, Sep 20, 2021, at 5:04 AM, Nikola Radovanovic wrote: > > > Hi, > When decoupling business from ORM model, dataclass passed to SA's > imperative mapper *map_imperatively* will receive SA's internals like for > example *_sa_instance_state* and *_sa_class_manager*. > > I am wondering, what would be the best way to have "pure" dataclass, > without SA internals? First thing to come to my mind is to perform query on > SA *Table* and use dict/namedtuple to populate dataclass. Are there > better approaches? I am in particular interested how this approach will > behave with partial and composite updates? Any recipe to recommend? > > > to accomplish that you use a registry, typically a weak-keyed one, where > keys are the classes / instances in use and the values are the class > managers and states. If you wanted to apply such a system to your classes > you would make use of the instrumentation extension system: > > https://docs.sqlalchemy.org/en/14/orm/extensions/instrumentation.html > > there's also an example of it : > > > https://docs.sqlalchemy.org/en/14/_modules/examples/custom_attributes/custom_management.html > > > > now as far as if you *should* do this. Absolutely not. The > instrumentation extension system is a very old and almost never used corner > of the API which I moved out of the main library some years ago due to its > complexity. adding a weakref lookup to all class/state instrumentation > lookups will add a palpable performance penalty to most ORM operations, and > the instrumentation extension is likely not without bugs and regressions at > this point. it was first created over ten years ago to suit the use case > of a single user who was working with Zope security proxied objects. > I've seen at least one other person using it, but overall i dont think it's > worthwhile to spend lots of time going down tunnels like this; if your > dataclass has a few attributes stuck on it, that shouldn't be a problem for > any real-world situation. > > > > > > > Thank you in advance. > > Kindest regards > > > -- > 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. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy/324223bc-695d-4479-be32-b1a7c73e8a76n%40googlegroups.com > > <https://groups.google.com/d/msgid/sqlalchemy/324223bc-695d-4479-be32-b1a7c73e8a76n%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/3d3b6d37-d833-41a8-b414-2f41e7c601c3n%40googlegroups.com.
