Question

Gurus – I’m stuck in a situation that I can’t figure out how I can query from the following collection “spouse”, which has embedded document “surname” and check for equality with “surname” of this document:

{
  "_id" : ObjectId("50bd2bb4fcfc6066b7ef090d"),
  "name" : "Gwendolyn",
  "surname" : "Davis",
  "birthyear" : 1978,
  "spouse" : {
    "name" : "Dennis",
    "surname" : "Evans",
    "birthyear" : 1969
  },  

I need to query:

Output data for all spouses with the same surnames (if the surname of
one of the spouses is not specified, assume that it coincides with the
name of another)

I tried something like this:

db.task.find( {“surname” : { “spouse.surname” : 1 }} )

but it failed)

PLEASE PLEASE Guide me how I can achieve this any example/sample? based on this will be really helpful 🙂

Thanks a lot!

Answer 1

You have three options.

1. Use $where modifier:

   db.task.find({$where: 'this.spouse.surname === this.surname'})

2. Update all your documents and add special flag. After that you will be able to query documents by this flag. It’s faster then $where, but requires altering your data.

3. Use MapReduce. It’s quite complicated, but it allows you to do nearly anything.