Question

What i am trying to do is the write a javascript function to access a defined articles schema in my .js file.

I have already determined that the below queries work in the mongodb terminal:

    db.articles.ensureIndex( { "comments.user_id" : 1 } )
        db.articles.find( { "comments.user_id" : 987654 } ) // returns all document fields, meaning X and Y including comments

        db.articles.find( { "comments.user_id" : 987654 }, 
{ "title" : 1, "comments.user_id" : 1 })   //some trimming

The purpose of the javascript function is to retrieve all comments made by a specific user, is my below attempt correct corresponding to the above mongodb queries? Are the style, syntax considered good practice?

exports.allCommentsByUser = function(userId){ 
   db.articles.ensureIndex({"comments.user_id" : 1})
    var allComments = db.articles.find({"comments.user_id" : userId}, 
                  { "title" : 1, "comments.user_id" : 1 });
    return allComments;
}

Q: Further, how do i convert the above javascript function to a closure function?

Note: i am using mongoose as a wrapper

Answer 1

That won’t work because allComments is a Mongoose Query object, not the results. You need to add a callback parameter to your allCommentsByUser method that the method will use to provide the results back to the caller once the async find call completes.

exports.allCommentsByUser = function(userId, callback){ 
    db.articles.find(
        {"comments.user_id" : userId}, 
        { "title" : 1, "comments.user_id" : 1 }, 
        callback);
};

Usage of the method:

x.allCommentsByUser(userId, function (err, articles) {
    if (err) {
        console.error(err);
    } else {
        console.log(articles);
    }
});

Not sure what you’re asking in your second question regarding a ‘closure function’.