Pymongo在成功的更新/删除操作后返回none。-Pymongoreturnsnoneaftersuccessfulupdate/removeoperations

1  

You're mixing the terms. The section of the documentation you highlighted is referring to the write acknowledgement not number of documents that were updated.

你是混合的。您突出显示的文档部分指的是写入确认，而不是更新的文档数量。

In short, when driver sends a write command to MongoDB and you have the the default write acknowledgment (w=1) the driver will throw an OperationFailure error if MongoDB doesn't confirm that the updated completed successful. You can read more details about it on the MongoDB pages.

简而言之，当驱动程序向MongoDB发送一个写命令，并且您有默认的写确认(w=1)时，如果MongoDB不确认更新完成的成功，那么驱动程序将抛出一个OperationFailure错误。您可以在MongoDB页面上阅读更多有关它的详细信息。

Both of your updates were actually successful (MongoDB confirmed that the update was applied). That's why you didn't get an error. Your problem is that your update query didn't actually update any documents.

您的两个更新实际上都是成功的(MongoDB确认了更新的应用)。这就是为什么你没有出错。您的问题是更新查询实际上并没有更新任何文档。

If you do that update in a MongoDB shell v2.6+, where no document are actually modified, you will get a result like this:

如果您在MongoDB shell v2.6+中进行更新，在没有修改文档的情况下，您将得到这样的结果:

WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 0 })

And the result for an update that actually changed a document will look like this:

更新后的结果是这样的:

WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

Edit:

编辑:

I was using the older version of pymongo (2.6.3) installed on Ubuntu with apt-get and I was getting the same response for the update query as you were getting.

我使用的是pymongo的旧版本(2.6.3)，安装在Ubuntu上的apt-get，我得到的更新查询的响应和你得到的一样。

I removed the python-pymongo package and updated to newest version of pymongo using pip. I got the following response from update that modified a document:

我删除了python-pymongo包并使用pip更新到最新版本的pymongo。我得到了修改后的更新文件的响应:

{'updatedExisting': True, u'nModified': 1, u'ok': 1, u'n': 1}

I tested this on MongoDB 2.6. using this code.

我在MongoDB 2.6上测试了这个。使用这个代码。

from pymongo import MongoClient

m = MongoClient('localhost', 27017)

db = m.test

print db.test.update({}, {'$pull': {'a'  : 1}})

Edit2

Edit2

That's because you're using MongoDB 2.4. If you're using sandbox/free versions on MongoHQ you can't currently change that (link).

这是因为您使用的是MongoDB 2.4。如果你在MongoHQ上使用沙箱/免费版本，你现在不能改变这个(链接)。

MongoDB 2.6 is returning updatedExisting field in the response to the update command (which is one that's important to you). I suspect that's because the changed write protocol in v 2.6:

MongoDB 2.6在对update命令的响应中返回updatedExisting字段(这对您来说很重要)。我怀疑这是因为v2.6中修改的写入协议:

A new protocol for write operations integrates write concerns with the write operations, eliminating the need for a separate getLastError command. Write methods now return the status of the write operation, including error information.

写操作的新协议将写操作与写操作集成在一起，消除了对单独的getLastError命令的需要。写方法现在返回写操作的状态，包括错误信息。

0  

I assume you're using pymongo.Connection, which does unacknowledged writes to MongoDB by default. Therefore Connection doesn't tell you the outcome of your update operation.

我猜你在用pymongo。连接，默认情况下不承认写入MongoDB。因此，连接不会告诉您更新操作的结果。

Connection is deprecated; you should use pymongo.MongoClient instead. MongoClient has many advantages, including that it does acknowledged writes by default. If you use MongoClient you'll get information about each update:

连接弃用;您应该使用pymongo。MongoClient代替。MongoClient有很多优点，包括默认情况下所写的。如果您使用MongoClient，您将获得关于每个更新的信息:

>>> import pymongo
>>> collection = pymongo.MongoClient().test.collection
>>> collection.insert({'_id': 1, 'array': ['a']})
1
>>> collection.update({'_id': 1}, {'$pull': {'array': 'a'}})
{u'nModified': 1, u'ok': 1, u'n': 1, 'updatedExisting': True, u'electionId': ObjectId('53a1a6bd30492fdb9fb5610a'), u'lastOp': Timestamp(1403111261, 1)}