Pull array within array - mongodb

Question

Similar to Find document with array that contains a specific value, but i'm trying to pull it.
db.getCollection('users').find({'favorites':{$elemMatch:{0:5719}}}, {"favorites.$": 1})
returns this:
{
"_id" : "FfEj5chmviLdqWh52",
"favorites" : [
[
5719,
"2016-03-21T17:46:01.441Z",
"a"
]
]
}
even after this returned 1:
Meteor.users.update(this.userId, {$pull: {'favorites':{$elemMatch:{0:movieid}}}})

Answer 1

It doesn't work because $pull is trying to remove a matching element from the "favorites" array. What you want to do is remove from the "array inside the array" of favorites.
For this you need a positional match to point to the nth inner element, then a very careful $pull expression to actually remove that element:
Meteor.users.update(
{ "favorites": { "$elemMatch": { "$elemMatch": { "$eq": 5719 } } } },
{ "$pull": { "favorites.$": 5719 } }
)
The "double" $elemMatch with the $eq operator is a bit more expressive than { 0: 5719 } since it is not "locked" into the first position only and is actually looking at the matching value. But you can write it that way if you must, or if you "really mean" to match that value in the first position only.
Note that the "index" returned from the match in the positional $ argument is actually that of the "outer" array. So to pull from the
Of course if there is only ever one nested array element within, the you might as well just write:
{ "$pull": { "favorites.0": 5719 } }
Using the direct "first index" position, since you know the inner array will always be there.
In either case, your object updates correctly:
{
"_id" : "FfEj5chmviLdqWh52",
"favorites" : [
[
"2016-03-21T17:46:01.441Z",
"a"
]
]
}
If you are trying to $pull the entire array entry from favorites, then the $eleMatch just needs to be dialed back one element:
Meteor.users.update(
{ "_id": this.userId },
{ "$pull": { "favorites": { "$elemMatch": { "$eq": 5719 } } } }
)
Or even:
Meteor.users.update(
{ "_id": this.userId },
{ "$pull": { "favorites": { "$elemMatch": { "0": 5719 } } } }
)
Noting that:
{ "_id": this.userId },
Is the long form that we generally use as a "query" selector, and especially when we want criteria "other than" the _id of the document. MiniMongo statements require at "least" the _id of the document though.
The rest of the statement has one "less" $elemMatch because the $pull already applies to the array.
That removes the whole matched element from the outer array:
{
"_id" : "FfEj5chmviLdqWh52",
"favorites" : []
}

Answer 2

This is the first code i found that actually works:
Meteor.users.update(Meteor.userId(), {$pull: {favorites: {$in: [i]}}})
Apparently $in does partial matching. It seems safer than the working code from this answer:
Meteor.users.update(
{ "_id": this.userId },
{ "$pull": { "favorites": { "$elemMatch": { "$eq": i } } } }
)