On 9/10/15 10:13 AM, Ladislav Lenart wrote:
Hello.
Just a really, really tiny and pedantic correction... The stack variable in the
code is in fact a queue. This could potentially surprise some users / readers.
To fix, please do one of the following:
* Rename stack local var to queue.
* Use stack.pop() to pop the last element from the stack.
there really should be some other name, because all the time, I have
routines like this where even dynamically within the routine, the pop(0)
is a pop() or vice-versa, because we'd like the iteration to work one
way or another. Changing pop(0) to pop() here means we are doing
depth-first instead of breadth-first. So. Some word that means
"collection of things to operate upon"? I've seen "work" used.
"buffer" ? eh.
HTH,
Ladislav Lenart
On 10.9.2015 15:48, Mike Bayer wrote:
On 9/10/15 9:35 AM, Mike Bayer wrote:
On 9/10/15 8:48 AM, Pavel S wrote:
Let's say, I have declarative classes A, B, C, D.
A is the parent
B has FK&relationship to A
C has FK&relationship to B,
D has FK&relationship to C etc...
I'd like to implement _generic method_ walk(obj) which will recursively yield
dependent/related objects of obj (which is instance of A).
I know that there is introspection interface inspect(), however I'm don't
really understand how to use it properly in my use case.
Shall I do inspect(obj) or rather inspect(obj.__class__) and then somehow
apply inspection to obj?
Are there an examples and best practices?
right now you can kind of get this effect using cascade_iterator:
http://docs.sqlalchemy.org/en/rel_1_0/orm/mapping_api.html?highlight=cascade_iterator#sqlalchemy.orm.mapper.Mapper.cascade_iterator
the limitation is that right now its based on relationship cascade settings,
as that's what it was intended for, so you'd probably want to use "save-update":
insp = inspect(my_object)
for obj in insp.mapper.cascade_iterator("save-update", insp):
# ...
to implement your own system, the graph of objects is strictly based on
relationship. so walk() is pretty simple:
def walk(obj):
yield obj
insp = inspect(obj)
for relationship in insp.mapper.relationships:
related = getattr(obj, relationship.key)
if relationship.uselist:
for collection_member in related:
for walk_related in walk(collection_member):
yield walk_related
elif related is not None:
for walk_related in walk(related):
yield walk_related
here's one im putting in the FAQ for now, which solves recursion depth as well
as cycles:
def walk(obj):
stack = [obj]
seen = set()
while stack:
obj = stack.pop(0)
if obj in seen:
continue
else:
seen.add(obj)
yield obj
insp = inspect(obj)
for relationship in insp.mapper.relationships:
related = getattr(obj, relationship.key)
if relationship.uselist:
stack.extend(related)
elif related is not None:
stack.append(related)
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