Remove element from array aggregate

Question

How can I loop through an array and remove a specific element based on a field.

Here is the layout I have - it is in a collection called cases:

** The collection contains a companyID, cases [Array], lastModified **

So I will have to use an aggregate to unwind the cases and then search for the casenumber where it equals '17':

db.cases.aggregate([
    { $match: { companyID: 218}},
    { $unwind: '$cases' },
    { $match: {'cases.casenumber': '17'} }
])

This returns:

But now I want to delete just that specific item.

Thanks.

So to be clear you want to remove all cases that have an casenumber set to 17? And by remove I mean remove the specific case element from the cases array. — Orelsanpls
– Orelsanpls, Commented Jan 31, 2020 at 10:51
@GrégoryNEUT Yes, although there will only be 1 with casenumber 17 but even if there were more that would be fine to remove. — Andrew
– Andrew, Commented Jan 31, 2020 at 10:55

Orelsanpls · Accepted Answer · 2020-01-31 11:00:34Z

2

You can use of an updateMany request. First argument is the matching condition, the second is the action.

$pull is a special keyword that will remove matching elements from arrays.

   db.collection.updateMany({
       companyID: 218,
    }, {
       $pull: {
          cases: {
             casenumber: 17,
          },
       },
    })

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

https://docs.mongodb.com/manual/reference/operator/update/pull/

Example from the doc :

db.profiles.update( { _id: 1 }, { $pull: { votes: { $gte: 6 } } } )

answered Jan 31, 2020 at 11:00

Orelsanpls

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4 Comments

Andrew Over a year ago

I looked into that but it wouldn't remove it - I thought it was possibly due to the fact that it needed to unwind the array first? It says Acknowledged is true, but matchedCount and modifiedCount are 0. Oh and just incase this makes a difference, 17 is a string. I have put the '' around it when testing

Orelsanpls Over a year ago

@Andrew I should reproduce your schema to try this one, unfortunately I have no time right now. I'll do it later if no one answered your question by then.

Andrew Over a year ago

Really sorry - this worked, I forgot to change the name of the collection. Thank you very much

Orelsanpls Over a year ago

Great! :) glad that you figured this one out

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