How to Sort an Embedded Array Field in MongoDB?

Sorting Nested Arrays in MongoDB

Problem:
How do you sort an embedded array field in a MongoDB document, such as the scores array in the student collection?

Proposed Solution:
Due to limitations in Mongo's native sorting capabilities, you need to use either application code or MongoDB Aggregation Framework to manipulate embedded arrays.

Aggregation Framework Solution:
Using the MongoDB Aggregation Framework, you can perform the following steps to sort the scores array in descending order:

1. Document Match: Match the desired document using a suitable index, if available.
2. Array Expansion: Unwind the scores array to create a stream of documents for each score.
3. Type Filtering: Filter the stream to select scores of a specific type (e.g., 'homework').
4. Sorting: Sort the scores in descending order.

Aggregation Example:

db.students.aggregate([
    // Initial document match
    { $match: {
        _id : 1
    }},
    // Expand scores array
    { $unwind: '$scores' },
    // Filter homework scores
    { $match: {
        'scores.type': 'homework'
    }},
    // Sort in descending order
    { $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
}

The above is the detailed content of How to Sort an Embedded Array Field in MongoDB?. For more information, please follow other related articles on the PHP Chinese website!