How to rename a field name inside array

[Alikhan_Oitan]

I wanted to rename field inside an array which looks like this:

{
  lessons: [
    {
      someField: someValue,
      groupId: 'some id string'
    },
    {
      someField: anotherValue,
      groupId: 'another id string'
    },
  ]
}

so I want to rename groupId field name to classid in every document and every lessons element. Firstly I wrote some JS script operation, but then I learned that eval is deprecated and as a result forEach and script operations cannot be used. What is the aggregation I could use in this situation, the complete aggregation is also very welcome, of course.

Thank you for your attention.

[turivishal (Vishal Turi)]

Hello @Alikhan_Oitan, Welcome to MongoDB Developer Forum ,

You can use update with aggregation pipeline starting from MongoDB 4.2,

• check query update only where groupId is exists
• $map to iterate loop of lessons and result your required fields

db.collection.update(
  { "lessons.groupId": { $exists: true } },
  [{
    $set: {
      lessons: {
        $map: {
          input: "$lessons",
          in: {
            classid: "$$this.groupId",
            someField: "$$this.someField"
          }
        }
      }
    }
  }],
  { multi: true }
)

[Alikhan_Oitan]

Thank you, @turivishal !

I also came up with this kind of solution just now, but I could not use it in java, since scriptOps has been deprecated.

I am using import org.springframework.data.mongodb.core. I am not expecting you to answer this, but in the official documents and google there are no examples on mapping using org.springframework.data.mongodb.core.aggregation.VariableOperators.Map. I am not sure why, maybe this is a new update. Could you please give some example in Java and specifically org.springframework.data.mongodb.core.aggregation.VariableOperators.Map.

I came up with something like this using autocomplete hints, but that’s all. I don’t know how to finish from here.

final Query deletedQuery = Query.query(Criteria.where("deleted").is(true));
Update groupToClassUpdate = new Update().set("lessons", Map.itemsOf("$lessons").as("lesson").andApply());
template.updateMulti(deletedQuery, groupToClassUpdate, Timetable.class);

But using "lessons.groupId": { $exists: true} is sure helpful. I would add that too.

Thank you for your help and reply @turivishal

[turivishal (Vishal Turi)]

I am really sorry, I’m not aware of java syntax, someone will help you with this or you can ask new post with java tag.

[Alikhan_Oitan]

Thanks! I appreciate your help! Will do! @turivishal