mongoose: Remove values in embeded document array using $pull (MongoDB 3.4 version)

Question

I am trying to remove values from nested array using mongoose in node js. My schema structure is like this:

    ([{_id: 1,


    results: [
      { item: "A", score: 5, answers: [ { q: 1, a: 4 }, { q: 2, a: 6 } ] },
      { item: "B", score: 8, answers: [ { q: 1, a: 8 }, { q: 2, a: 9 } ] }
   ]
},
{
   _id: 2,
   results: [
      { item: "C", score: 8, answers: [ { q: 1, a: 8 }, { q: 2, a: 7 } ] },
      { item: "B", score: 4, answers: [ { q: 1, a: 0 }, { q: 2, a: 8 } ] }
   ]
}])

I want to remove values from answers where a is 8. my query is

db.collection.update({"results.item":{$in:["C","B"]}},{$pull:{"results.$.answers":{a:8}}})

This query is working fine but updating only one document. Please help.

my desired output is

([{
   _id: 1,
   results: [
      { item: "A", score: 5, answers: [ { q: 1, a: 4 }, { q: 2, a: 6 } ] },
      { item: "B", score: 8, answers: [ { q: 2, a: 9 } ] }
   ]
},
{
   _id: 2,
   results: [
      { item: "C", score: 8, answers: [ { q: 2, a: 7 } ] },
      { item: "B", score: 4, answers: [ { q: 1, a: 0 } ] }
   ]
}])

Thanks in advance.

@Sam That's wrong. So please don't encourage the wrong answer either. — Neil Lunn
– Neil Lunn, Commented Mar 4, 2019 at 13:20

Neil Lunn · Accepted Answer · 2019-03-04 13:39:29Z

1

You need filtered positional $[<identifier>] support from MongoDB 3.6 or greater for a single statement:

db.collection.updateMany(
  { "results.item": { "$in": ["C","B"] } },
  { "$pull": { "results.$[el].answers": { "a": 8 } } },
  { "arrayFilters":  [{ "el.item": { "$in": ["C", "B"] } }] }
)

Results in:

{
        "_id" : 1,
        "results" : [
                {
                        "item" : "A",
                        "score" : 5,
                        "answers" : [
                                {
                                        "q" : 1,
                                        "a" : 4
                                },
                                {
                                        "q" : 2,
                                        "a" : 6
                                }
                        ]
                },
                {
                        "item" : "B",
                        "score" : 8,
                        "answers" : [
                                {
                                        "q" : 2,
                                        "a" : 9
                                }
                        ]
                }
        ]
}
{
        "_id" : 2,
        "results" : [
                {
                        "item" : "C",
                        "score" : 8,
                        "answers" : [
                                {
                                        "q" : 2,
                                        "a" : 7
                                }
                        ]
                },
                {
                        "item" : "B",
                        "score" : 4,
                        "answers" : [
                                {
                                        "q" : 1,
                                        "a" : 0
                                }
                        ]
                }
        ]
}

answered Mar 4, 2019 at 13:39

Neil Lunn

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3 Comments

Neil Lunn Over a year ago

@Thamaraiselvam Because "B" is in two documents. That's the only reason.

Thamaraiselvam Over a year ago

Ahh...🤷‍♂️🤷‍♂️🤷‍♂️🤷‍♂️🤷‍♂️🤷‍♂️

Anshul Jain Over a year ago

Thank you Neil Lunn for the right solution This solution works perfect as expected on MongoDB version 3.6 and above but My application is currently running on MongoDB 3.4. Is their any solution which can work on 3.4 version?

Thamaraiselvam · Accepted Answer · 2019-03-04 13:16:09Z

0

By default, the update() method updates a single document. Set the Multi Parameter to update all documents that match the query criteria.

set {multi: true} or Use updateMany

Reference: https://docs.mongodb.com/manual/reference/method/db.collection.update/

answered Mar 4, 2019 at 13:16

Thamaraiselvam

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3 Comments

Anshul Jain Over a year ago

Thanks for replying very soon. I used this db.collection.update({"results.item":{$in:["C","B"]}},{$pull:{"results.$.answers":{a:8}}}, {multi:true}). this is working but from one document it is removing only one value for example from _id: 2 document it should remove one object from item "C" and one from item "B" but by this query it removes only from item "C"

Neil Lunn Over a year ago

That's not the part that does this. Updating "multiple array elements" is different to "multiple documents".

Neil Lunn Over a year ago

That's why I answered.

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