BEES INC wrote:
>
> phwoar, ok. I think I understand.
>
> To break it down:
>
> I have a class Foo which, among other things, contains a dict called
> vals with keys of dates and values of floats.
>
> When I store an instance of Foo, it goes to the foo table, and any
> items in the vals dict should go into the vals table.
>
> For sql alchemy to understand how to store the items from the vals
> dict, i need an ORM(?) object that describes a single row in the vals
> table.
>
> This manifests as a python object called Val, which for my case has a
> datetime and float scalar. This maps to the datatypes of the vals
> table, i.e. one row in the vals table will have a datetime and a
> float.
>
> class Val(object):
> def __init__(self, key, value):
> self.date = key
> self.val = value
>
> Then, in the mapping of the Foo object, I create a relation with the
> Val object called vals_dict, which is a column_mapped_collection with
> a key of Val.date. This manifests as Foo.vals_dict, which is a dict
> with datetime keys and Val object as the value.
>
> mapper(Foo, foo, properties = dict(
> vals_dict = relation(Val, secondary=foo_vals, collection_class
> = column_mapped_collection(vals.c.date))
> ))
>
> Since a dict with a datetime key giving a Val object is somewhat
> unwieldy to work with, i create an AssociationProxy called Foo.vals,
> which when accessed by a given key, returns the 'val' attribute of the
> given Val object.
>
> Foo.vals = association_proxy('vals_dict', 'val')
>
> Which seems to do what I want :)
>
> Have I understood this correctly, and is this the right way to do it?
>
> Thank you for your patience, I am still somewhat new to SQLAlchemy and
> ORM's in general.
you're good to go, nice job !
>
> #!/usr/bin/env python2.6
>
> from sqlalchemy import *
> from sqlalchemy.orm import sessionmaker, mapper, relation
> from sqlalchemy.orm.collections import column_mapped_collection
> from sqlalchemy.ext.associationproxy import association_proxy
>
> from datetime import datetime
>
> class Val(object):
> def __init__(self, key, value):
> self.date = key
> self.val = value
>
> class Foo(object):
>
> def __init__(self, name):
> self.name = name
>
> engine = create_engine('sqlite:///:memory:', echo=True)
> meta = MetaData(bind=engine)
>
> vals = Table('vals', meta,
> Column('id', Integer, primary_key=True),
> Column('date', DateTime),
> Column('val', Float),
> )
>
> foo = Table('foo', meta,
> Column('id', Integer, primary_key=True),
> Column('name', String(50))
> )
>
> foo_vals = Table('foo_vals', meta,
> Column('foo_id', Integer, ForeignKey('foo.id'), primary_key=True),
> Column('val_id', Integer, ForeignKey('vals.id'), primary_key=True)
> )
>
> mapper(Val, vals)
>
> mapper(Foo, foo, properties = dict(
> vals_dict = relation(Val, secondary=foo_vals, collection_class =
> column_mapped_collection(vals.c.date))
> ))
>
> Foo.vals = association_proxy('vals_dict', 'val')
>
> meta.create_all()
>
> Session = sessionmaker(bind=engine)
> session = Session()
>
> f = Foo('hello')
> f.vals[datetime(2009, 9, 28)] = 1.0
>
> f2 = Foo('hello again')
> f2.vals[datetime(2008, 8, 28)] = 2.0
>
> session.add(f)
> session.add(f2)
> session.commit()
>
> print "%s -> %s" % (f.name, f.vals)
> print "%s -> %s" % (f2.name, f2.vals)
>
> print f.vals_dict
> for x in f.vals_dict:
> print "x = %s" % x
> y = f.vals_dict[x]
> print "y = %s" % y
> print "y.date = %s, y.val = %s" % (y.date, y.val)
>
> On Sun, Sep 27, 2009 at 5:59 AM, Michael Bayer <[email protected]>
> wrote:
>>
>>
>> On Sep 26, 2009, at 1:25 PM, BEES INC wrote:
>>
>>> class Vals(dict): pass
>>>
>>> class Foo(object):
>>>
>>> def __init__(self, name):
>>> self.vals = Vals()
>>> self.name = name
>>>
>>> def add(self, key, value):
>>> self.vals[key] = value
>>
>> you would need to say self.vals[key] = Vals() here.
>> column_mapped_collection uses full ORM instances as values. In any
>> case I don't think you mean to map the "vals" table to a "dict"
>> subclass - the mapping of a table to a class implies how to represent
>> a single *row*, not the full table as a whole.
>>
>> If you are attempting to map from scalar keys to scalar (non object)
>> values, you should look into using the AssociationProxy to accomplish
>> that.
>>
>>
>>
>>
>>>
>>> engine = create_engine('sqlite:///:memory:', echo=True)
>>> meta = MetaData(bind=engine)
>>> Session = sessionmaker(bind=engine)
>>>
>>> vals = Table('vals', meta,
>>> Column('id', Integer, primary_key=True),
>>> Column('date', DateTime),
>>> Column('val', Integer),
>>> Column('foo_id', Integer, ForeignKey('foo.id'))
>>> )
>>>
>>> mapper(Vals, vals)
>>>
>>> foo = Table('foo', meta,
>>> Column('id', Integer, primary_key=True),
>>> Column('name', String(50))
>>> )
>>>
>>> mapper(Foo, foo, properties = dict(
>>> vals = relation(Vals, collection_class = column_mapped_collection
>>> (vals.c.date))
>>> ))
>>>
>>> sess = Session()
>>> meta.create_all()
>>>
>>> f = Foo('hello')
>>> f.add(datetime.now(), 1.0)
>>>
>>>
>>> >
>>
>>
>> >
>>
>
> >
>
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~----------~----~----~----~------~----~------~--~---
