Question

Is there any way to update nested documents by id or some other field?

I use “Full Tree in Single Document” and don’t know beforehand how deep nesting can go. Need to Update, for example, answer with {id:’104′}. I can do that via ‘dot notation’, but since I don’t know the level (depth) of nesting I can’t predict how long my 'comment.answers.answers....answers.' can go.

Is there any way to directly find and update id:’104′, or I still need to pass some kind of depth mark?

{
 title:'some title',
 comment:
     {
        id:'101'
        author:'Joe',
        text:'some comment',
        answers:
        [
            {
              id:'102'
              author:'Joe',
              text:'first answer to comment',
              answers:
                    [
                       {
                           id:'103'
                           author:'Done',
                           text:'first answer to first answer to comment',
                           answers:[]
                       },
                       {
                           id:'104'
                           author:'Bob',
                           text:'Second answer to first answer to comment',
                           answers:[]
                       }

                    ]

            },

            {
            },

            {
            },
        ]
     }
}

I use The Node.JS MongoDB Driver

Answer 1

In short there’s no really good way to do a query of this sort. There are a few options:

You can create a query with a long $or statement, specifying each of the possible nested locations for the document:

{ comment.id: 103, $or [
                        { comment.answers.id: 103 }, 
                        { comment.answers.answers.id: 103 },
                        { comment.answers.answers.answers.id: 103 } 
                       ] 
}

For more information about the $or operator see the docs.

In truth, the better and more sustainable solution would be to use a different schema, where all comments and answers are stored in a flat array and then store information about the relationships between the comments in a comments.parent field. For example:

 { comment: [
           { id: 1 }
           { id: 2, parent: 1 }
          ] }

For additional options and a more in depth discussion of possible ways of modeling comment hierarchies, view the Storing Comments Use Case in the MongoDB documentation.

There are also a number of also strategies in the Trees in MongoDB that you might want to consider.