I’ll introduce a sample query for retrieving Array type fields sorted by length in MongoDB.

MongoDB Query

db.posts.aggregate(
[
  { $unwind: "$likes" },
  { $group: {
      _id: "$_id",
      size: { $sum: 1 }
    }
  },
  { $sort: { size: -1 } }
])

Results

{ "_id" : ObjectId("514e23e06aeaa880410321aa"), "size" : 590 }
{ "_id" : ObjectId("545c796972b4c28015ab4eac"), "size" : 395 }
{ "_id" : ObjectId("51440f7d4ca4c41367001dff"), "size" : 321 }
{ "_id" : ObjectId("51d6eef05204c9046100031d"), "size" : 315 }
{ "_id" : ObjectId("54ae81f1f158d13d60c50116"), "size" : 271 }
//...

Reference Information

• mongodb - Mongo order by length of array - Stack Overflow

That’s all from the Gemba.