Mongodb subfield select

Question

Hello I have the following db:

My question is how do I "SELECT name FROM posts Where thread=Sloan"

Because I'm trying into RockMongo shell : "db.users.find({"posts.thread":'Sloan'})" but it's return all the collection data

***** Using json-generator.com ********************

[
            '{{repeat(5, 7)}}',
            {
                id: '{{index}}',
                group: '{{surname}}',
                name: '{{firstName}} {{surname}}',

                posts: [
                    '{{repeat(25)}}',
                    {
                        thread:'{{surname}}',
                        sb:[
                            '{{repeat(100)}}',
                            {
                                id: '{{index}}',
                                name: '{{firstName}} {{surname}}'

                            }
                        ]
                    }
                ],

                users:[
                    '{{repeat(25)}}',
                    {
                        name:'{{firstName}}'
                    }]


            }
        ]

Answer 1

To clarify thing a little... if you have a database looking like this:

Then if you do db.users.find({ posts: { $elemMatch: { thread: "Sloan" } } }), you will obtain this (every element posts are included):

And if you do db.users.find({"posts.thread":'Sloan'},{'posts.$':1}), you will obtain this (only the relevant post is included):

(By the way, it's faster to perform... and if you add an index on posts.thread, it will be even faster.)

One last thing, which I think can be misleading here. The db.users.find({ posts: { $elemMatch: { thread: "Sloan" } } }, { name: 1 }) projection will give the element name 'gloria sharpe', but from what I understand from the question, he would prefer to obtain the name which is post.thread.sb.name. That's why he wants to have only the relevant post as an answer and not all the posts of that element.