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MongoDB Academy · Lesson

Positional and Filtered Positional Updates

Learners will update matched array elements in place using the $ positional operator and the $[identifier] filtered positional operator.

Updating Elements Inside Arrays

While $push and $pull add and remove array elements, sometimes you need to modify an existing element in place—change a field inside a sub-document that is already in the array. MongoDB provides two positional operators for this: the $ positional operator for updating the first matching element, and the $[identifier] filtered positional operator for updating all matching elements.

The $ Positional Operator

The $ positional operator acts as a placeholder for the index of the first array element that matched the query filter. You use it in the update's field path like 'arrayField.$.subField', and MongoDB replaces $ with the index of the matched element. The query filter must include a condition on the array field so MongoDB knows which element to target.

// Update the grade of the first matching scores element
db.students.updateOne(
  {
    _id: studentId,
    'scores.subject': 'math'  // match condition identifies which element
  },
  {
    $set: { 'scores.$.grade': 'A+' }  // $ = index of matched element
  }
);
// Only the FIRST element where subject='math' is updated

All lessons in this course

  1. Querying Arrays: $all, $size, and Element Match
  2. $elemMatch: Matching Array Sub-Documents
  3. Updating Arrays: $push, $pull, $pop, $addToSet
  4. Positional and Filtered Positional Updates
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