Mongo {$ne : null} not working as expected - mongodb

Question

When I issue the following query:
db.users.find({"pic.status" : {$ne : null} }, {"pic" : 1}).toArray()
I expect to receive all users whose pic.status is NOT null. However, the actual result looks something like this:
{
"_id" : ObjectId("4f1e1ab9cdf9dbaa160000bf"),
"pic" : {
"id" : "4f1e1ab9cdf9dbaa160000be",
"status" : null
}
},
{
"_id" : ObjectId("4f1e28480eaf38193d00006f"),
"pic" : {
"id" : "4f1e28480eaf38193d00006e",
"status" : null
}
}
That is, I receive users whose pic.status IS null. How can I fix this?

Answer 1

I know it's an old question, and might not be relevant anymore, but as there was no accepted answer, I thought I'll comment for anyone looking for answer.
I was able to reproduce the problem on MongoDB version 2.4.9.
> db.sourceListings.findOne({displayed:{$ne:null}});
{
<.. other stuff went here..>
"displayed" : null
}
The problem disappears on Version 2.6.1:
> db.sourceListings.findOne();
{
<.. other stuff ..>
"displayed" : null
}
> db.sourceListings.findOne({displayed:{$ne:null}});
null
Probably was fixed somewhere in between these two versions.

Answer 2

I cannot seem to reproduce this. What version of Mongo are you using? (I am using 2.1.1-pre) Here are the steps that I took. The following is from the JS shell:
> db.users.save({
"_id" : 1,
"pic" : {
"id" : "4f1e1ab9cdf9dbaa160000be",
"status" : null
}
});
> db.users.save({
"_id" : 2,
"pic" : {
"id" : "4f1e28480eaf38193d00006e",
"status" : null
}
});
> db.users.save({
"_id" : 3,
"pic" : {
"id" : "4f1e28480eaf38193d00006e",
"status" : "Something"
}
});
> db.users.find({"pic.status":{$ne:null}}, {pic:1}).toArray()
[
{
"_id" : 3,
"pic" : {
"id" : "4f1e28480eaf38193d00006e",
"status" : "Something"
}
}
]
Only the document containing "pic.status":"Something" is returned.
My only thought is, are you absolutely certain that the value of (null) in the query is the same as what is saved in the documents? Were the documents saved using the JS shell, or were they saved using a driver in a different language? Theoretically, null, should be null, should be null, in any language, but I know that different languages represent "no value" differently. In python, for example, the value for "no value" is (None). (null) is not recognised in python.
In a python shell, I attempted to save a document with (null) as a value, but received an error:
In [13]: coll.save({"_id":5, "pic":{"id":5, "status":null}})
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
/Users/mbastien/mongodb-osx-x86_64-2.0.1/bin/<ipython-input-13-1ad232456c88> in <module>()
----> 1 coll.save({"_id":5, "pic":{"id":5, "status":null}})
NameError: name 'null' is not defined
I then inserted (with the Python shell) a status of 'null' ('null' being a string)
In [15]: coll.save({"_id":5, "pic":{"id":5, "status":'null'}})
Out[15]: 5
Not surprisingly, when I reran the query in the JS shell, this document was returned, because 'null' != null
> db.users.find({"pic.status":{$ne:null}}, {pic:1}).toArray()
[
{
"_id" : 3,
"pic" : {
"id" : "4f1e28480eaf38193d00006e",
"status" : "Something"
}
},
{
"_id" : 5,
"pic" : {
"status" : "null",
"id" : 5
}
}
]
Is this similar to what you are experiencing, or can you reproduce this 100% in the JS shell? Hopefully, we will be able to get to the root of this issue!

Answer 3

Use $nin with a single element in the array. It'll behave as you expect. KI with many of the people who use mongo.