python - MongoEngine 抛出异常 TypeError : cannot deepcopy this pattern object

Question

我在使用列表和正则表达式查询查询 mongodb 模型(Python/MongoEngine)时遇到异常。代码是

from mongoengine import *
import re 

db = connect('testdb')

class Team(Document):
    name = StringField()
    groups = ListField(ReferenceField('Group'))

class Group(Document):
    name = StringField()

Team.drop_collection()
Group.drop_collection()

g1 = Group('G1')
g1.save()

g2 = Group('G2')
g2.save()

g3 = Group('G3')
g3.save()

g4 = Group('G4')
g4.save()

t = Team('Team1',[g1,g2,g3])
t.save()

t = Team('Team2',[g1,g2,g4])
t.save()

t = Team('Team3',[])
t.save()

t = Team('Team3',[g3,g2])
t.save()

t = Team('Team3',[g4,g1])
t.save()


# TypeError: cannot deepcopy this pattern object
teams = Team.objects( Q(groups__in=[g3,g2]) & Q(name=re.compile('eam3')))
for team in teams:
   print team.name  


#-------------------------

异常回溯是

Traceback (most recent call last):
  File "so_mongoengine_query.py", line 46, in <module>
    for team in teams:
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/queryset.py", line 81, in _iter_results
    self._populate_cache()
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/queryset.py", line 93, in _populate_cache
    self._result_cache.append(self.next())
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/base.py", line 1137, in next
    raw_doc = self._cursor.next()
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/base.py", line 1182, in _cursor
    self._cursor_obj = self._collection.find(self._query,
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/base.py", line 1215, in _query
    self._mongo_query = self._query_obj.to_query(self._document)
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/visitor.py", line 91, in to_query
    query = self.accept(SimplificationVisitor())
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/visitor.py", line 141, in accept
    return visitor.visit_combination(self)
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/visitor.py", line 41, in visit_combination
    return Q(**self._query_conjunction(queries))
  File "/usr/local/lib/python2.7/dist-packages/mongoengine/queryset/visitor.py", line 61, in _query_conjunction
    combined_query.update(copy.deepcopy(query))
  File "/usr/lib/python2.7/copy.py", line 163, in deepcopy
    y = copier(x, memo)
  File "/usr/lib/python2.7/copy.py", line 257, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib/python2.7/copy.py", line 174, in deepcopy
    y = copier(memo)
TypeError: cannot deepcopy this pattern object

Update-1:以下代码生成相同的异常

query = ( Q(groups__in=[g3,g2]) & Q(name=re.compile('eam3')))
copy.deepcopy(query)

有什么建议吗？ 谢谢

Answer 1

因为 Python 不支持编译后的正则表达式模式的深层复制(since Python 2.5)，即

copy.deepcopy(re.compile('eam3'))

不受支持。 mongoengine 在组合多个查询对象时将使用 copy.deepcopy。因此，如果您使用单个正则表达式过滤器，则查询可以使用 mongoengine，但不能使用多个。

mongoengine 支持一组字符串查询，你可能会找到它们in the document .