Mongo $ne fails on the client when there are multiple items in a sub collection

[pjelar]

Put this in your startup:

    Meteor.startup(function () {

        var testid_1 = Test.insert({name: "Test" });
        var testid_2 = Test.insert({name: "Test2" });
        Test.update({_id: testid_1}, {
            $push: { bets:{userid: "CZskWsJymrqwrdWjT", username: "John Wayne" } } });
        Test.update({_id: testid_1}, {
            $push: { bets:{userid: "Lgh25FM93jz6KFvGJ", username: "Clint Eastwood" } } });
        Test.update({_id: testid_2}, {
            $push: { bets:{userid: "CZskWsJymrqwrdWjT", username: "John Wayne" } } });
        Test.update({_id: testid_2}, {
            $push: { bets:{userid: "Lgh25FM93jz6KFvGJ", username: "Clint Eastwood" } } });
    });

On the client console:

Test.find( {'bets.userid': {$ne: "Lgh25FM93jz6KFvGJ"} }).count()
2

On the server, either through minimongo or using a meteor server side method:

> db.test.find( {'bets.userid': {$ne: "Lgh25FM93jz6KFvGJ"} }).count()
0

[glasser]

Thanks for the report. Yeah, the precise semantics of how Mongo selectors interact with arrays (not to mention, eg, multiple levels of arrays) is undocumented and varies from selector type to selector type. eg, for some things, {x: {$foo: 5}} means (if x is an array) "there is at least one element of the array such that {$foo: 5} is true". For others, it means "for all elements of the array, {$foo: 5}" is true (eg, that's the case for $ne).

I know that Mongo is rewriting the matcher for 2.5 and I think they may be doing it in a way that makes their code easier to understand. Taking a look at that might help us do better at accurately implementing array queries.

[pjelar]

As a workaround how would you go about removing the items in the same way the $ne would?

[larssonp-tmg]

As a work around I'm adding the userid like this:

Test.update({_id: testid_1}, {
            $push: { userid: "CZskWsJymrqwrdWjT" }});

Then $ne works

[glasser]

I think that you can actually use $not as a workaround here: {'bets.userid': {$not: "Lgh25FM93jz6KFvGJ"}}

I am going to try to fix $ne today, though.

@larssonp-tmg is correct that we currently handle this inconsistently based on whether the array is the bottom level of the key or a higher level.

[glasser]

Oops, my workaround does not work.