example-push-with-multiple-modifiers.rst

A collection students has the following document:

{
   "_id" : 5,
   "quizzes" : [
                  { wk: 1, "score" : 10 },
                  { wk: 2, "score" : 8 },
                  { wk: 3, "score" : 5 },
                  { wk: 4, "score" : 6 }
               ]
}

The following :update:`$push` operation uses:

• the :update:`$each` modifier to add multiple documents to the quizzes array,
• the :update:`$sort` modifier to sort all the elements of the modified quizzes array by the score field in descending order, and
• the :update:`$slice` modifier to keep only the first three sorted elements of the quizzes array.

db.students.update( { _id: 5 },
                    { $push: { quizzes: { $each: [ { wk: 5, score: 8 },
                                                   { wk: 6, score: 7 },
                                                   { wk: 7, score: 6 } ],
                                          $sort: { score: -1 },
                                          $slice: 3
                                        }
                             }
                    }
                  )

The result of the operation is keep only the three highest scoring quizzes:

{ "_id" : 5,
  "quizzes" : [
                { "wk" : 1, "score" : 10 },
                { "wk" : 2, "score" : 8 },
                { "wk" : 5, "score" : 8 }
              ]
}