On Mon, Jul 24, 2017 at 4:40 AM, Ruben Di Battista <rubendibatti...@gmail.com> wrote: > Thanks for taking the time to answer. > > Doing what you say means that then I have to import the models classes from > the sql.py module instead of the models.py. Am I right?
your top example shows the model classes Order and Item being imported into sql.py already so that you can call mapper() on them. Based on that setup, I proposed putting the association_proxy declaration right there. Or the > association_proxy attribute is then available to the original class (as it > happens when using mapper)? I'm not super familiar with the automagic of > SQLAlchemy... The association proxy is a Python descriptor, which is a basic component of Python and worth knowing about: https://docs.python.org/3/howto/descriptor.html > > On Mon, Jul 24, 2017 at 1:50 AM, Mike Bayer <mike...@zzzcomputing.com> > wrote: >> >> On Sun, Jul 23, 2017 at 11:26 AM, Ruben Di Battista >> <rubendibatti...@gmail.com> wrote: >> > Hello, >> > >> > I'm trying to introduce database persistence into an already existent >> > class >> > hierarchy. That mean I have in a separate module all the class >> > representing >> > the models of my application (without SQL interaction methods), then I >> > have >> > in another module the SQL schema and the mapping (so I'm using the >> > classical >> > mapping): >> > >> > sql.py >> > >> > import sqlalchemy.orm as orm >> > from sqlalchemy import Metadata, Integer, String, DateTime >> > from myproject.models import Item, Order >> > >> > metadata = MetaData() >> > >> > item = Table('item', metadata, >> > Column('id', Integer, primary_key=True), >> > Column('name', String), >> > Column('quantity', Integer) >> > ) >> > >> > order = Order('order', metadata, >> > Column('id', Integer, primary_key=True), >> > Column('date', DateTime), >> > ) >> > >> > orm.mapper(Item, item) >> > orm.mapper(Order, order) >> > >> > >> > >> > >> > models.py >> > class Item(object): >> > def __init__(self, name, quantity): >> > self.name = name >> > self.quantity = quantity >> > >> > class Order(object): >> > def __init__(self, date): >> > self.date = date >> > >> > Now I would like to introduce a M2M relationship with additional column >> > in >> > the association table: >> > >> > order_item = Table('order_item', metadata, >> > Column('order_id', Integer, ForeignKey('order.id')), >> > Column('item_id', Integer, ForeignKey('item.id')), >> > Column('price', Float) >> > ) >> > >> > >> > In the documentation, when they present the Association proxy, they do >> > that >> > in a declarative way. So they add an attribute to the class: >> > >> > # ... Class definition ... >> > items = association_proxy('order_items', 'items') >> > >> > >> > Is there a way to achieve this without touching the classes in >> > models.py? >> > Maybe using the orm.mapper? Or the only way is to modify the class >> > adding >> > the association proxy like in the documentation? Do you have any >> > reference >> > to point me out on the right direction to use association proxies with >> > classical mapping? >> >> Basically, just do this: >> >> orm.mapper(Order, order) >> Order.items = association_proxy('order_items', 'items') >> >> The association proxy is independent of the declarative system and if >> you look in early documentation you'll see it described in terms of >> classical mapping. >> >> As far as the term "without touching the classes", there's not much >> point trying to be purist about this as the call to mapper(Order, >> order) highly alters the Order class in any case. >> >> >> > >> > Thanks, >> > >> > PS: You find this same question on SO, if you want you can answer also >> > there. >> > >> > >> > >> > -- >> > 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. >> >> -- >> 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. 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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. -- 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. 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