MongoDB copy a field to another collection with a foreign key

Question

I want to copy over the color from user collection to the Car collection. I\'m using a foreign key which is userID.

> db.test1.User.find()
{ \"_id\" : Obj         


        

Answer 1

Here are my two cents: you can drop "function(x)". I prefer the following syntax:

db.source_collection_name.find().forEach(
  doc=>
      db.target_collection_name.update(
        {"_id": doc._id},
        {$set: {"field_to_update": doc.field}}
      )
)

In your case, something like this should work:

db.test1.User.find().forEach(
  doc=> 
    db.test2.Car.update( 
      { "userID": doc._id }, 
      { $set: { "color": doc.Color} } 
    ) 
);