Geek Answers Handbook

Sqlalchemy many to many, but vice versa?

I apologize if inversion is not the preferred nomenclature that may have interfered with my search. In any case, I am dealing with two declarative sqlalchemy classes, which are many-to-many relationships. The first is an account, and the second is a collection. Users "buy" collections, but I want to show the first 10 collections that the user has not yet purchased .

from sqlalchemy import *
from sqlalchemy.orm import scoped_session, sessionmaker, relation
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

engine = create_engine('sqlite:///:memory:', echo=True)
Session = sessionmaker(bind=engine)

account_to_collection_map = Table('account_to_collection_map', Base.metadata,
                                Column('account_id', Integer, ForeignKey('account.id')),
                                Column('collection_id', Integer, ForeignKey('collection.id')))

class Account(Base):
    __tablename__ = 'account'

    id = Column(Integer, primary_key=True)
    email = Column(String)

    collections = relation("Collection", secondary=account_to_collection_map)

    # use only for querying?
    dyn_coll = relation("Collection", secondary=account_to_collection_map, lazy='dynamic')

    def __init__(self, email):
        self.email = email

    def __repr__(self):
        return "<Acc(id=%s email=%s)>" % (self.id, self.email)

class Collection(Base):
    __tablename__ = 'collection'

    id = Column(Integer, primary_key=True)
    slug = Column(String)

    def __init__(self, slug):
        self.slug = slug

    def __repr__(self):
        return "<Coll(id=%s slug=%s)>" % (self.id, self.slug)

So, with account.collections I can get all the collections, and with dyn_coll.limit (1) .all () I can apply queries to the list of collections ... but how can I do the opposite? I would like to get the first 10 collections that the account does not .

Any help is incredibly appreciated. Thank!

+5
1

, , ( , .., ). IMO, , , :

class Account(Base):
    ...
    # please note added *backref*, which is needed to build the 
    #query in Account.get_other_collections(...)
    collections = relation("Collection", secondary=account_to_collection_map, backref="accounts")

    def get_other_collections(self, maxrows=None):
        """ Returns the collections this Account does not have yet.  """
        q = Session.object_session(self).query(Collection)
        q = q.filter(~Collection.accounts.any(id=self.id))
        # note: you might also want to order the results
        return q[:maxrows] if maxrows else q.all()
...
+5

More articles:


All Articles