Question 400791 in Mongodb Question posted in
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MongoDB – Overwrite the whole array field instead of its item

I have this schema:{ key: [] }. I want to convert it to { key: { foo: number } }.

This is the query I came up with:

db.collection.update({}, [
  {
    "$set": {
      key: { foo: 43 }
    }
  }
], { multi: true })

However, it updates the individual array item instead of the array as a whole. I.e. the document:

{ key: [1, 2] }

becomes :

{ key: [ { foo: 43 }, { foo: 43 } ] }

instead of:

{ key: { foo: 43 } }.

I just want to get rid of the original array completely. I can just remove the field, then write the update. But is there a way to do it in one fell swoop?

Update: I have to use the pipeline, there’re other stuff going on.

Tags:

2

Answers


  1. 0

    As per this comment:

    I just want to get rid of the original array completely. I don’t use the original value.

    In that case, don’t use the pipeline syntax for update. So you only need to remove the [...] surrounding $set:

    db.collection.update({},
{
  "$set": {
    key: { foo: 43 }
  }
},
{ multi: true })

    And if you do need an update pipeline for some other steps, then unset key before setting a new value:

    db.collection.update({},
[
  { $unset: "key" },
  {
    $set: {
      key: { foo: 43 }
    }
  }
],
{ multi: true }
)

    Mongo Playground

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  2. 0

    Use $literal

    db.collection.update({},
[
  {
    "$set": {
      "key": {
        "$literal": {
          "foo": 43
        }
      }
    }
  }
])

    Mongo Playground

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