Question

I am storing Tweets in a MongoDB database, and would like to use Field Selectors (http://www.mongodb.org/display/DOCS/Querying#Querying-FieldSelection) to return just the text, the date and the screen name of the user.

{ 
    "_id" : NumberLong("213686009408"), 
    "text" : "RT @Milanello: Lightning over the Donb...", 
    "created_at" : "Fri, 15 Jun 2012 17:37:38 +0000", 
    "user" : { 
        "screen_name" : "xxxxx", 
        "profile_image_url" : "http://a0.twimg.com/pro[...].jpg"
    }
}

Creating a query that returns just the text and date is easy enough:

> db.abc.find({},{created_at:1,text:1})

I’m not sure how to return the user.screen_name property as well?

[UPDATE]

I had previously tried using the dot notation and it threw an exception, however, as per both answers below (I have +1’d both) the dot notation does work, but only if you use “” around the attribute names.

So, this does NOT work:

db.abc.find({},{created_at:1,text:1, user.screen_name:1})

But this DOES:

db.abc.find({},{created_at:1,text:1, "user.screen_name":1})

Answer 1

You can use dot notation as you would in a query:

db.abc.find({},{created_at:1,text:1, "user.screen_name" : 1})

However, the field will not be flattened, so the result objects still have a user-subdocument:

{ "_id" : NumberLong("4546545"), 
  "created_at" : "Fri, 15 Jun...", 
  "user" : { "screen_name" : "John Doe" } 
}

However, flattening this in code shouldn’t be a big problem.