>
>
> Whoops - occasionally a session autoflush can break the function above - a
> better version delays the session.add() calls until the relationships have
> been built:
from sqlalchemy.inspection import inspect
from sqlalchemy.orm import class_mapper
import logging
log = logging.getLogger(__name__)
def copy_sqla_object(obj, omit_fk=True):
"""
Given an SQLAlchemy object, creates a new object (FOR WHICH THE OBJECT
MUST SUPPORT CREATION USING __init__() WITH NO PARAMETERS), and copies
across all attributes, omitting PKs, FKs (by default), and relationship
attributes.
"""
cls = type(obj)
mapper = class_mapper(cls)
newobj = cls() # not: cls.__new__(cls)
pk_keys = set([c.key for c in mapper.primary_key])
rel_keys = set([c.key for c in mapper.relationships])
prohibited = pk_keys | rel_keys
if omit_fk:
fk_keys = set([c.key for c in mapper.columns if c.foreign_keys])
prohibited = prohibited | fk_keys
log.debug("copy_sqla_object: skipping: {}".format(prohibited))
for k in [p.key for p in mapper.iterate_properties
if p.key not in prohibited]:
try:
value = getattr(obj, k)
log.debug("copy_sqla_object: processing attribute {} =
{}".format(
k, value))
setattr(newobj, k, value)
except AttributeError:
log.debug("copy_sqla_object: failed attribute {}".format(k))
pass
return newobj
def deepcopy_sqla_object(startobj, session, flush=True):
"""
For this to succeed, the object must take a __init__ call with no
arguments. (We can't specify the required args/kwargs, since we are
copying
a tree of arbitrary objects.)
"""
objmap = {} # keys = old objects, values = new objects
log.debug("deepcopy_sqla_object: pass 1: create new objects")
# Pass 1: iterate through all objects. (Can't guarantee to get
# relationships correct until we've done this, since we don't know
whether
# or where the "root" of the PK tree is.)
stack = [startobj]
while stack:
oldobj = stack.pop(0)
if oldobj in objmap: # already seen
continue
log.debug("deepcopy_sqla_object: copying {}".format(oldobj))
newobj = copy_sqla_object(oldobj)
# Don't insert the new object into the session here; it may trigger
# an autoflush as the relationships are queried, and the new objects
# are not ready for insertion yet (as their relationships aren't
set).
# Not also the session.no_autoflush option:
# "sqlalchemy.exc.OperationalError: (raised as a result of Query-
# invoked autoflush; consider using a session.no_autoflush block if
# this flush is occurring prematurely)..."
objmap[oldobj] = newobj
insp = inspect(oldobj)
for relationship in insp.mapper.relationships:
log.debug("deepcopy_sqla_object: ... relationship: {}".format(
relationship))
related = getattr(oldobj, relationship.key)
if relationship.uselist:
stack.extend(related)
elif related is not None:
stack.append(related)
# Pass 2: set all relationship properties.
log.debug("deepcopy_sqla_object: pass 2: set relationships")
for oldobj, newobj in objmap.items():
log.debug("deepcopy_sqla_object: newobj: {}".format(newobj))
insp = inspect(oldobj)
# insp.mapper.relationships is of type
# sqlalchemy.utils._collections.ImmutableProperties, which is
basically
# a sort of AttrDict.
for relationship in insp.mapper.relationships:
# The relationship is an abstract object (so getting the
# relationship from the old object and from the new, with e.g.
# newrel = newinsp.mapper.relationships[oldrel.key],
# yield the same object. All we need from it is the key name.
log.debug("deepcopy_sqla_object: ... relationship: {}".format(
relationship.key))
related_old = getattr(oldobj, relationship.key)
if relationship.uselist:
related_new = [objmap[r] for r in related_old]
elif related_old is not None:
related_new = objmap[related_old]
else:
related_new = None
log.debug("deepcopy_sqla_object: ... ... adding: {}".format(
related_new))
setattr(newobj, relationship.key, related_new)
# Now we can do session insert.
log.debug("deepcopy_sqla_object: pass 3: insert into session")
for newobj in objmap.values():
session.add(newobj)
# Done
log.debug("deepcopy_sqla_object: done")
if flush:
session.flush()
return objmap[startobj] # returns the new object matching startobj
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