In MongoDB, how does on get the value in a field for an embedded document, but query based on a different value

问题

I have a basic structure like this:

> db.users.findOne()
{
    "_id" : ObjectId("4f384903cd087c6f720066d7"),
    "current_sign_in_at" : ISODate("2012-02-12T23:19:31Z"),
    "current_sign_in_ip" : "127.0.0.1",
    "email" : "something@gmail.com",
    "encrypted_password" : "$2a$10$fu9B3M/.Gmi8qe7pXtVCPu94mBVC.gn5DzmQXH.g5snHT4AJSZYCu",
    "last_sign_in_at" : ISODate("2012-02-12T23:19:31Z"),
    "last_sign_in_ip" : "127.0.0.1",
    "name" : "Trip Jameson",
    "sign_in_count" : 100,
    "usertimes" : [
        ...thousands and thousands of records like this one....
        {
            "enddate" : 348268392.115282,
            "idle" : 0,
            "startdate" : 348268382.116728,
            "title" : "My Awesome Title"
        },
    ]
}

So I want to find only usertimes for a single user where the title was "My Awesome Title", and then I want to see what the value for "idle" was in that record(s)

So far all I can figure out is that I can find the entire user record with a search like:

> db.users.find({'usertimes.title':"My Awesome Title"})

This just returns the entire User record though, which is useless for my purposes. Am I misunderstanding something?

回答1:

Return only partial embedded documents is currently not supported by MongoDB The matching User record will always be returned (at least with the current MongoDB version).

see this question for similar reference

Filtering embedded documents in MongoDB

This is the correspondent Jira on MongoDB space

http://jira.mongodb.org/browse/SERVER-142

回答2:

Use:

db.users.find({'usertimes.title': "My Awesome Title"}, {'idle': 1});

May I suggest you take a more detailed look at http://www.mongodb.org/display/DOCS/Querying, it'll explain things for you.

来源：https://stackoverflow.com/questions/9253838/in-mongodb-how-does-on-get-the-value-in-a-field-for-an-embedded-document-but-q