Question 115748 in Mongodb Question posted in
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MongoDB how to add field assinged by another filed

I have a collection in MongoDb someCollection containing field field1.
I want to add another field with values equal to field1. I do it like this:

db.someCollection.updateMany({}, {$set:{"newField": "$field1"}})

But the after update I got row like this

{"field1": "value1", "newField": "$field1"}

But expected result is:

{"field1": "value1", "newField": "value1"}

What is wrong?

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2

Answers


  1. 0

    You can use update with pipeline. It looks almost the same, but the second part uses []:

    db.someCollection.updateMany({}, [{$set:{"newField": "$field1"}}])

    See how it works on the playground example

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  2. 0

    Try this one:

    db.someCollection.updateMany({}, [{$set:{"newField": {$expr: {$field: "field1"}}}]})
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