Hi,
in my following example I don't know how to properly delete items in
an ordered list. I can't call items.remove (as I would violate the
"items must be in a list rule"). If I delete the item, the list order
get's not updated. Is there a way to automate the necessary reorder
call for this case? Additinally, what is the proposed way to reorder
an ordered list such that the positions are updated automatically?
Best,
André
PS: I'm running SQLAlchemy 0.5.4p2 on Python 2.6. The program first
prints <Item item2 part of <List list> at position 2>, which is
wrong, and after the explicit reorder call it prints the correct <Item
item2 part of <List list> at position 1>.
-------------------------------------------
# -*- encoding: utf-8 -*-
from sqlalchemy import create_engine, MetaData, Table, Column,
Integer, Unicode, ForeignKey, UniqueConstraint
from sqlalchemy.orm import sessionmaker, mapper, relation
from sqlalchemy.ext.orderinglist import ordering_list
metadata = MetaData()
list_table = Table("list", metadata,
Column("id", Integer, primary_key=True),
Column("name", Unicode, unique=True))
item_table = Table("item", metadata,
Column("id", Integer, primary_key=True),
Column("position", Integer),
Column("name", Unicode, unique=True),
Column("list_id", Integer, ForeignKey("list.id"),
nullable=False),
UniqueConstraint("list_id", "name"))
class List(object):
def __init__(self, name):
self.name = name
def __repr__(self):
return "<List %s>" % self.name
class Item(object):
def __init__(self, name, list=None):
self.name = name
self.list = list
def __repr__(self):
return "<Item %s part of %s at position %s>" % (self.name,
self.list, self.position)
mapper(List, list_table,
properties={"items": relation(Item,
backref="list",
order_by=[item_table.c.position],
collection_class=ordering_list
("position"))})
mapper(Item, item_table)
engine = create_engine("postgres:///list", echo=False)
metadata.bind = engine
list_table.create()
item_table.create()
Session = sessionmaker(engine)
session = Session()
l = List(u"list")
i1 = Item(u"item1", l)
i2 = Item(u"item2", l)
i3 = Item(u"item3")
l.items.insert(1, i3)
session.add(l)
session.commit()
# everything is fine up to this point. Now I want to delete item1 from
the list:
# l.items.remove(i1) # will violate the not null constraint of
item.list_id
session.delete(i1) # will not update the positions of the other items!
print "before explicit reorder:", i2
l.items.reorder() # does fix the positions -- is this the proposed
solution???
print "after explicit reorder:", i2
# also: what is the proposed solution to reorder the items, say I want
to move i1 to the end of the list?
session.commit()
session.close()
engine.dispose()
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