将 mongoengine 与多处理一起使用 - 如何关闭 mongoengine 连接？

Question

无论我尝试什么，在尝试在 mongoengine db 上使用多处理时，我都会一直点击“MongoClient opens before fork”关于不分叉活动 mongo 连接的警告。 standard mongo advice 似乎只能从子进程中连接到数据库，但我认为我正在做的事情在功能上应该是等效的，因为我在使用多处理之前关闭了数据库但是我仍然遇到了问题。

没有最小示例或不适用解决方案的相关问题是here、here，特别是针对flask/celery 和here的情况

重现问题的最小示例：

from mongoengine import connect, Document, StringField, ListField, ReferenceField
from pathos.multiprocessing import ProcessingPool


class Base(Document):
    key = StringField(primary_key=True)
    name = StringField()
    parent = ReferenceField('Parent', required=True)

class Parent(Document):
    key = StringField(primary_key=True)
    name = StringField()
    bases = ListField(ReferenceField('Base'))


def remove_base(key):
   db = connect('mydb')
   mongo_b = Base.objects().get(key=key)
   mongo_b.parent.update(pull__bases=mongo_b)
   mongo_b.delete()


### setup
db = connect('mydb', connect=False)

Base(key='b1', name='test', parent='p1').save()
Base(key='b2', name='test', parent='p1').save()
Base(key='b3', name='test2', parent='p1').save()

p=Parent(key='p1', name='parent').save()
p.update(add_to_set__bases='b1')
p.update(add_to_set__bases='b2')
p.update(add_to_set__bases='b3')

### find objects we want to delete
my_base_objects = Base.objects(name='test')
keys = [b.key for b in my_base_objects]
del my_base_objects

# close db to avoid problems?!
db.close()
del db

# parallel map removing base objects and references from the db
# warning generated here
pp = ProcessingPool(2)
pp.map(remove_base, keys)

Answer 1

好的，我想通了。 Mongoengine 在各处缓存与数据库的连接。如果您手动删除它们，那么问题就解决了。添加以下导入

from mongoengine import connection

然后添加：

connection._connections = {}
connection._connection_settings ={}
connection._dbs = {}

Base._collection = None
Parent._collection = None

到“#close db”部分似乎可以解决问题。

完整代码：

from mongoengine import connect, Document, StringField, ListField, ReferenceField, connection
from pathos.multiprocessing import ProcessingPool


class Base(Document):
    key = StringField(primary_key=True)
    name = StringField()
    parent = ReferenceField('Parent', required=True)

class Parent(Document):
    key = StringField(primary_key=True)
    name = StringField()
    bases = ListField(ReferenceField('Base'))


def remove_base(key):
   db = connect('mydb', connect=False)
   mongo_b = Base.objects().get(key=key)
   mongo_b.parent.update(pull__bases=mongo_b)
   mongo_b.delete()

def setup():
    Base(key='b1', name='test', parent='p1').save()
    Base(key='b2', name='test', parent='p1').save()
    Base(key='b3', name='test2', parent='p1').save()

    p=Parent(key='p1', name='parent').save()
    p.update(add_to_set__bases='b1')
    p.update(add_to_set__bases='b2')
    p.update(add_to_set__bases='b3')

db = connect('mydb', connect=False)
setup()
### find objects we want to delete
my_base_objects = Base.objects(name='test')
keys = [b.key for b in my_base_objects]
del my_base_objects


### close db to avoid problems?!
db.close()
db = None

connection._connections = {}
connection._connection_settings ={}
connection._dbs = {}

Base._collection = None
Parent._collection = None

### parallel map removing base objects from the db
pp = ProcessingPool(2)
pp.map(remove_base, keys)

Answer 2

最近对此进行了改进，从 MongoEngine>=0.18.0 开始，应使用方法 disconnect() 和 disconnect_all() 分别断开 1 个或所有现有连接 (changelog 0.18.0)

见官方doc