How to Sort Embedded Arrays in MongoDB in Descending Order?

Sorting Embedded Array in MongoDB

Question:

How can I sort the scores array within each student record in a MongoDB collection in descending order of score?

Problem:

Consider the following student record:

{
  "_id": 1,
  "name": "Aurelia Menendez",
  "scores": [
    {
      "type": "exam",
      "score": 60.06045071030959
    },
    {
      "type": "quiz",
      "score": 52.79790691903873
    },
    {
      "type": "homework",
      "score": 71.76133439165544
    },
    {
      "type": "homework",
      "score": 34.85718117893772
    }
  ]
}

An attempt to manually iterate over the scores array using embedded JavaScript in the mongo shell prompts an error.

Solution:

To sort the scores array, consider the following MongoDB Aggregation Framework pipeline:

db.students.aggregate(
  // Match the document (uses index if suitable)
  { $match: {
      _id: 1
  }},
  // Unwind scores array
  { $unwind: '$scores' },
  // Filter to specific score type (optional)
  { $match: {
      'scores.type': 'homework'
  }},
  // Sort scores array
  { $sort: {
      'scores.score': -1
  }}
)

Output (Sample):

{
  "result": [
    {
      "_id": 1,
      "name": "Aurelia Menendez",
      "scores": {
        "type": "homework",
        "score": 71.76133439165544
      }
    },
    {
      "_id": 1,
      "name": "Aurelia Menendez",
      "scores": {
        "type": "homework",
        "score": 34.85718117893772
      }
    }
  ],
  "ok": 1
}

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