Remove Part of an array mongodb

Question

Hi i am attmepting to remove anything after the first value e.g.

Collection:{

"_id' :.....
"UrlId" : "5dfc1aa2986b7c30f3398be4",
    "coverInput" : 
           [
            "https://test.com/s/files/1/00351576213050",
            "https://test.com.au"
           ],

}

what I want to replace the document with is:

Collection:{

"_id' :.....
"UrlId" : "5dfc1aa2986b7c30f3398be4",
    "coverInput" : 
           [
            "https://test.com/s/files/1/00351576213050"
           ],

}

Im sure this is something simple. I tried this but got an error:

db.test.aggregate([
{
    $addFields: {
        coverInput: { $substr: [ "$coverInput", 0, { $indexOfBytes: [ "$coverInput", "," ] } ] }
    }
}
]).forEach( doc => db.test.updateOne( { _id: doc._id }, { $set: { coverInput: doc.coverInput } } ) )

Thanks in advance!

$substr operator is used to work with strings. You have to use Aggregation array operators to work with array fields. — prasad_
– prasad_, Commented Jan 8, 2020 at 9:39

Ashh · Accepted Answer · 2020-01-08 09:24:28Z

1

You can use below aggregation

db.collection.aggregate([
  { "$project": {
    "coverInput": {
      "$slice": ["$coverInput", 1]
    }
  }}
])

Or if you want to update the document

db.test.updateOne(
  { _id: doc._id },
  [{
    $set: { coverInput: { "$slice": ["$coverInput", 1] } }
  }]
)

answered Jan 8, 2020 at 9:24

Ashh

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