mongoengine
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hmarr
.append() to a ListField(ReferenceField()) silently fails under specific circumstances
"""
Demonstrate a somewhat obscure bug with ListField(ReferenceField()).
1) Create an object with an empty ListField(ReferenceField()).
- the field can either be left empty (using the default value),
or you can explicity set it to empty.
- issue does not occur with ListField(StringField())
- if an object is appended now (before first persist) problem does not occur.
2) Save the object and reload it.
3) Append an entity to the ListField(ReferenceField()).
- the object will be silently dropped.
- setting the field to a list containing the item is a workaround.
- if an object had been added to the list in step 1, adding the
second object now would be fine.
"""
from mongoengine import *
import sys
class Dog(Document):
name = StringField ()
puppies = ListField(ReferenceField('Dog'))
def test ():
connect ('testdb')
Dog.drop_collection ()
# Create dog with empty puppies list
rover0 = Dog (name='Rover')
# Turning this on does not fix the problem
if False:
rover0.puppies = []
# If you turn this on, both this case, and the after-reload case will work fine.
if False:
puppy0 = Dog (name='puppy0')
puppy0.save ()
rover0.puppies.append (puppy0)
print 'Added a puppy before initial save', [p.name for p in rover0.puppies]
# Save the dog
rover0.save ()
# Load the same dog again
rover1 = Dog.objects(name='Rover').get ()
# Create and persist a puppy
puppy1 = Dog (name='puppy1')
puppy1.save ()
# Turning this on does not fix the problem
if False:
rover1.puppies = []
# Append the puppy to the puppies list
rover1.puppies.append (puppy1)
if puppy1 not in rover1.puppies:
print '*** Whoops: puppy did not get appended:', [p.name for p in rover1.puppies]
# This works however
rover1.puppies = rover1.puppies + [puppy1]
print 'Using workaround, all is good:', [p.name for p in rover1.puppies]
if __name__ == '__main__':
test ()
I have (approximately) the same issue, and it took me a long time to find this old bug report. In my case I don't even load the object again. I save it, then try to add an item, and save it again. This silently fails. Is this bug fixed in version 0.9 or taken into account?
