MongoDB concatenate strings from two fields into a third field

Question

How do I concatenate values from two string fields and put it into a third one?

I\'ve tried this:

db.collection.update(
  { \"_id\": { $exists: true          


        

Answer 1

You can use aggregation operators $project and $concat:

db.collection.aggregate([
  { $project: { newfield: { $concat: [ "$field1", " - ", "$field2" ] } } }
])