I have a query collection in mongodb which contains document in the below format :

{
    _id : ObjectId("61aced92ede..."),
    query : "How to solve...?",
    answer : []
    is_solved : false
}

Now, I want to filter the documents with the following condition

1. filter all documents that are not solved. (is_solved : true)

2. filter "n" number of document that are solved.

So, That result will have all unsolved documents and only 10 solved documents in an array.

CodePudding user response：

You can use this aggregation query:

• First use $facet to create two ways: The document solved, and document not solved.
• Into each way do the necessary $match and $limit the solved documents.
• Then concatenate the values using $concatArrays.

db.collection.aggregate([
  {
    "$facet": {
      "not_solved": [
        {
          "$match": {
            "is_solved": false
          }
        }
      ],
      "solved": [
        {
          "$match": {
            "is_solved": true
          }
        },
        {
          "$limit": 10
        }
      ]
    }
  },
  {
    "$project": {
      "result": {
        "$concatArrays": [
          "$not_solved",
          "$solved"
        ]
      }
    }
  }
])

Example here where I've used $limit: 1 to see easier.

Also, if you want, you can add $unwind at the end of the aggregation to get values at the top level like this example