mongodb: how to update array element by index number

Question

Suppose you have documents like this:

{
    _id: 'sdsdfsd',
    a: [
          { x: 0, y: 0, z: 0 }
          { x: 0, y: 0, z: 0 }
          { x: 0, y: 0, z: 0 }
          { x: 0, y: 0, z: 0 }
    ]
}

So, if you have the _id and an index number (say: 2). Now, for that index I want to change the x value to 1. Is this possible in mongo or should I first retrieve the whole array, update the specific value and update the whole array by inserting it back ?

JohnnyHK · Accepted Answer · 2014-05-08 16:47:20Z

7

You can access a specific array element in an update by its 0-based index using dot-notation:

// Set the x property of the third element of a to 1
db.test.update({_id: 'sdsdfsd'}, {$set: {'a.2.x': 1}})

answered May 8, 2014 at 16:47

JohnnyHK

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Uptimist · Accepted Answer · 2022-05-27 08:42:45Z

1

Else you can go further, you can construct your way to the value with the variable indexes. Use string template

   yourModel.findOneAndUpdate(
     { _id: "sdsdfsd" },
     {
       $set: {
         [`a.${index}.x`]: newValue,
       },
     }
   );

answered May 27, 2022 at 8:42

Uptimist

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