Confused as to how $pullAll works in MongoDB

Question

I've got a document that looks like this:

db.blog.findOne()
{
        "_id" : ObjectId("4dc1c938c4bfb4d21a000001"),
        "blogid" : 1,
        "body" : "Lorem ipsum dolor",
        "comments" : [
                {
                        "id" : 1,
                        "name" : "Alex",
                        "comment" : "Test",
                        "approved" : 1
                },
                {
                        "id" : 2,
                        "name" : "Phil",
                        "comment" : "Test",
                        "approved" : 1
                },
                {
                        "id" : 3,
                        "name" : "Joe",
                        "comment" : "Test",
                        "approved" : 0
                }
        ],
        "no_comments" : 11,
        "title" : "Hello world"
}

If I run the query

db.blog.update({'blogid':1}, { $pull : { 'comments' : {'approved' : 0} } });

Then it will remove the third comment.

If instead I want to pull all comments where approved is 0 or 1 the following query doesn't work:

db.blog.update({'blogid':1}, { $pullAll : { 'comments' : {'approved' : [0,1]} } });

I get the error

Modifier $pushAll/pullAll allowed for arrays only

Can someone please explain where I'm going wrong?

Thank you

Answer 1

db.blog.update({"blogid":1},{$pullAll:{"comments":{"name":"Phil","comment":{$eq:"Test"}}}})

WriteResult({
        "nMatched" : 0,
        "nUpserted" : 0,
        "nModified" : 0,
        "writeError" : {
                "code" : 2,
                "errmsg" : "$pullAll requires an array argument but was given a object"
        }
})

db.blog.update({"blogid":1},{$pull:{"comments":{"name":"Phil","comment":{$eq:"Test"}}}})

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

$pull update operator:

• It works if the element is either array or array with Object.
• It works even if you use any condition operator in query syntax.

$pullAll update operator:

• It only works if the element is array.
• It only works if you don't use any condition operator in query syntax