How do I create an Array of objects from a comma separated string field in MongoDB?

Question

I have three documents that looks like this:

_id: ObjectId('61e1312ad435c7124aa883a1')
name: "Brian"
languages: "English,Spanish,French"

_id: ObjectId('52e1312ad435c7124aa883a2')
name: "Max"
languages: "English"

_id: ObjectId('37e1312ad435c7124aa883a9')
name: "Mike"
languages: ""

As you can see, the languages field can either be empty, have one item, or multiple items separated by commas.

I want to create a new field, that is an Array of objects. Each object should consist of a "name" property and an "active" boolean. "name" should be the language and "active" should just be set to false. The end result should look like this:

_id: ObjectId('61e1312ad435c7124aa883a1')
name: "Brian"
languages: "English,Spanish,French"
newLanguages: [
    { name: "English", active: false },
    { name: "Spanish", active: false },
    { name: "French", active: false }
]

_id: ObjectId('52e1312ad435c7124aa883a2')
name: "Max"
languages: "English,Spanish,French"
newLanguages: [
    { name: "English", active: false }
]

_id: ObjectId('37e1312ad435c7124aa883a9')
name: "Mike"
languages: ""
newLanguages: []

I've managed to turn the comma-separated strings into the objects I want, but it doesn't create a new property, it just overwrites the languages property:

db.collection.updateMany({},
[
  {
    $set: {
      languages: {
        $filter: {
          input: {$split: ["$languages", ","]},
          cond: {$gt: [{$strLenCP: "$$this"}, 0]}
        }
      }
    }
  },
  {
    $set: {
      languages: {
        $map: {
          input: "$languages",
          as: "item",
          in: {name: "$$item", active: false}
        }
      }
    }
 }
])

mongoplayground.net/p/9v_B-daEQzQ

nimrod serok
– nimrod serok

2022-06-14 09:04:39 +00:00
Commented Jun 14, 2022 at 9:04 — nimrod serok
– nimrod serok, Commented Jun 14, 2022 at 9:04

nimrod serok · Accepted Answer · 2022-06-14 09:06:30Z

1

Simply set a new key newLanguages, instead of the existing key languages, which will stay as it was:

db.collection.updateMany({},
[
  {
    $set: {
      newLanguages: {
        $filter: {
          input: {$split: ["$languages", ","]},
          cond: {$gt: [{$strLenCP: "$$this"}, 0]}
        }
      }
    }
  },
  {
    $set: {
      newLanguages: {
        $map: {
          input: "$newLanguages",
          as: "item",
          in: {name: "$$item", active: false}
        }
      }
    }
 }
])

See how it works on the playground example

answered Jun 14, 2022 at 9:06

nimrod serok

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