How to loop through a nested array of objects in mongo and nodejs?

Question

I have a collection of posts each of which look something like this:

{Post: 
    [ 
        id: 'post_id',
        postedBy: 'user_id',
        likes: [0: id: 'user_id', 1: id: 'user_id'],
        content: 'text here',
        comments: [0: {id: 'comment_id', text: 'text here', postedBy: 'user_id'},
                   1: {id: 'comment_id', text: 'text here', postedBy: 'user_id']
        image: {url: 'image url here'}
    ],
    [ 
        id: 'post_id',
        postedBy: 'user_id',
        likes: [0: id: 'user_id', 1: id: 'user_id'],
        content: 'text here',
        comments: [0: {id: 'comment_id', text: 'text here', postedBy: 'user_id'},
                   1: {id: 'comment_id', text: 'text here', postedBy: 'user_id']
        image: {url: 'image url here'}
    ],
}

I want to be able to find all the comments that were created by a specific user, across all of the posts .

I know I can find posts created by a specific user by doing something like:

const post = await Post.find({ postedBy: some user_id });

I also know that if I knew the index of the comment I was looking for I could do something like:

const comment = await Post.find({ comments[0].postedBy: some user_id })

But I am struggling to work out how I can loop through a nested array of indexed objects like this to find the data I need. TIA

Answer 1

From the docs I discovered the $elemMatch operator and with this I was able to access all posts that contained a comment written by a specific user like this:

const posts = await Post.find({
  comments: { $elemMatch: { postedBy: user_id } },
});

I could then map through the returned array to access the comments themselves like this:

const comments = posts.map((item) => item.comments);

Hope this might help somebody else some day