Hello list,
I'm trying to learn Sqlalchemy. After reading the docs I decided to
create an example to test what I had learned so far. I usually do this
by creating a unittest.TestCase class and testing if everything is
working according to what I expect it to.
Meanwhile I'm having a bit of a problem handling deleted elements.
I've picked up your 'backref_tree' example and added some testcases to
explain my problem: after deleting the elements of a relation the
other side - the attribute - of the relation is not refreshed after a
objectstore.commit() followed by a objectstore.clear(). Is this the
expected behaviour, if it is can you please explain me why? The
problem is that this will raise inconsistencies and obligate all the
reference objects to be refreshed.
Another question why does the 'clear' method must be called after a
'commit'? If I'm committing my change isn't it expected that all the
remaining queries be flushed into the server?
On a side note, the deleting objects part is really missing on the
docs. There are no example on how deleting objects affect the
remaining "ecosystem", hence my confusion.
Thanks in advance,
--
Tiago Cogumbreiro <[EMAIL PROTECTED]>
http://s1x.homelinux.net/
from sqlalchemy import *
import sqlalchemy.attributes as attributes
engine = create_engine('sqlite://', echo=True)
class Tree(object):
def __init__(self, name='', father=None):
self.name = name
self.father = father
def __str__(self):
return '<TreeNode: %s>' % self.name
def __repr__(self):
return self.__str__()
table = Table('tree', engine,
Column('id', Integer, primary_key=True),
Column('name', String(64), nullable=False),
Column('father_id', Integer, ForeignKey('tree.id'), nullable=True),)
assign_mapper(Tree, table,
properties={
# set up a backref using a string
#'father':relation(Tree, foreignkey=table.c.id,primaryjoin=table.c.father_id==table.c.id, backref='childs')},
# or set up using the backref() function, which allows arguments to be passed
'childs':relation(Tree, foreignkey=table.c.father_id, primaryjoin=table.c.father_id==table.c.id, backref=backref('father', uselist=False, foreignkey=table.c.id))},
)
table.create()
root = Tree('root')
child1 = Tree('child1', root)
child2 = Tree('child2', root)
child3 = Tree('child3', child1)
objectstore.commit()
assert root.father is None
assert child1 in root.childs
assert child2 in root.childs
assert len(root.childs) == 2
assert child3 in child1.childs
assert len(child1.childs) == 1
assert len(Tree.select()) == 4, Tree.select()
child1.delete()
objectstore.commit()
objectstore.clear() # Why does the 'clear' method called explicitly
assert len(Tree.select()) == 3, Tree.select()
new_root = Tree.select_by(name="root")[0]
new_child3 = Tree.select_by(name="child3")[0]
assert child1 not in new_root.childs
assert new_child3.father is None
# Fails
assert child3.father is None
assert child1 not in root.childs, root.childs
