Mongoose fails to updateMany with $switch operator-CodePudding

I tried to use an example in the official document of mongodb,

db.students3.updateMany({ },
[
 { $set: { grade: { $switch: {
                       branches: [
                           { case: { $gte: [ "$average", 90 ] }, then: "A" },
                           { case: { $gte: [ "$average", 80 ] }, then: "B" },
                           { case: { $gte: [ "$average", 70 ] }, then: "C" },
                           { case: { $gte: [ "$average", 60 ] }, then: "D" }
                       ],
                       default: "F"
 } } } }
])

Property grade is defined as Number type. I got the error, when tried to update all documents in the database students3,

CastError: Cast to Number failed for value "{ '$switch': { branches: [ [Object] ] } }" (type Object) at path "grade"

Could someone explain the error? Thanks.

CodePudding user response：

You have to $trunc first, then average field would be created.

{ $set: { average : { $trunc: [ { $avg: "$tests" }, 0 ] }, modified: "$$NOW" } }

complete update

db.collection.update({},
[
  {
    $set: {
      average: { $trunc: [ { $avg: "$tests" }, 0 ] },
      modified: "$$NOW"
    }
  },
  {
    $set: {
      grade: {
        $switch: {
          branches: [
            { case: { $gte: [ "$average", 90 ] }, then: "A" },
            { case: { $gte: [ "$average", 80 ] }, then: "B" },
            { case: { $gte: [ "$average", 70 ] }, then: "C" },
            { case: { $gte: [ "$average", 60 ] }, then: "D" }
          ],
          default: "F"
        }
      }
    }
  }
])

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