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? 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...
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.
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> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
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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.
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