Node.js- Add new field in array of Mongodb object

Question

I have a collection of users that has an array of multiple plates :

users : [
{
_id: '61234XXX'
plates: [
 {
   _id: '123'
   'color': 'orange'
 },
 {
   _id: '124'
   'color': 'blue'
 }
]
},
{
_id: '63456XXX'
plates: [
 {
   _id: '321'
   'color': 'orange'
 },
 {
   _id: '432'
   'color': 'green'
 }
]
}
]

I'm trying to figure out a way to add a new field to the all current plate objects for every user:

I've got to this:

  await User.findOneAndUpdate(
      { _id: '63456XXX' },
      {
        $set : {
          [`plates.0.plateStyle`]: "testValue"
        }
      }
  )

Tho this works it's not fit for purpose. Is there a better way I can iterate over this?

J.F. · Accepted Answer · 2023-01-09 23:38:46Z

1

You can try this query:

Here you are using array filters to tell mongo: "Where you find an object with _id: "61234XXX" and exists the plates then, there, get the document (elem) which match that plates is not empty (to get all) and add plateStyle".

await User.updateMany({
  _id: "61234XXX",
  plates: {
    $exists: true
  }
},
{
  $set: {
    "plates.$[elem].plateStyle": "testValue"
  }
},
{
  arrayFilters: [
    {
      elem: { $ne: [ "$plates", [] ] }
    }
  ]
})

Example here

Also if you are finding by _id you won't need updateMany since _id is unique and only will be 1 or 0 results.

edited Jan 9, 2023 at 23:38

answered Jan 9, 2023 at 21:00

J.F.

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4 Comments

Gurneet Singh Over a year ago

Hey! Thanks for taking the time! unfortunately that doesn't work, the example you shared only shows it updating the first object in the array

J.F. Over a year ago

Sorry, my mistake, the trick is to use array filters.

Gurneet Singh Over a year ago

Thanks! If you could, could you explain whats happening here? { elem: { $ne: [ "$_id", null ] } the $ne onwards has thrown me off and can't find its ref in the docs

J.F. Over a year ago

$ne is "not equal". Here is used to match all documents which _id is not equal to null. Also in the link I've used $ne: ["$plates",[]] which I think is better. This is to match all elements where exists the array plates. What is basically you want, if exists the array, update the element.

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