In mongodb how do I replace array field with null value to an empty array-CodePudding

I want to replace an array field in document that has value of null to an empty array []. I tried this query but it's not working. Please help.

Basically I want testArray: null to be testArray: []

db.myTestCollection.aggregate( { "_id": ObjectId('1120191011212112') },
   [ { $set: { testArray: { $ifNull: [ { $concatArrays: [ "$testArray", [] ] } ] } } }
])

CodePudding user response：

Looks like you mostly have a syntax error. But you can also move the $ifNull logic into the filter predicate as well so that no update is considered/applied if the existing testArray field isn't already null. So:

db.collection.update({
  _id: 1,
  "testArray": null
},
[
  {
    $set: {
      testArray: []
    }
  }
])

Working playground example here.