Mongoose recursive query parent reference

Question

Mongoose recursive query parent reference

I am trying to do exactly what this mongo example is doing but in mongoose. It seems more complex to me in mongoose. Possibly i'm trying to fit a square peg in a round hole?

This example is from http://www.codeproject.com/Articles/521713/Storing-Tree-like-Hierarchy-Structures-With-MongoD (tree structure with parent reference)

I'm trying to build a path.

var path=[];
var item = db.categoriesPCO.findOne({_id:"Nokia"});
while (item.parent !== null) {
    item=db.categoriesPCO.findOne({_id:item.parent});
    path.push(item._id);
}
path.reverse().join(' / ');

Thanks!

javascript
node.js
mongodb
mongoose

Answer 1

Mongoose is an asynchronous library, so

db.categoriesPCO.findOne({_id:"Nokia"});

doesn't return the answer to the query, it just returns a Query object itself. In order to actually run the query, you'll need to either pass in a callback function to findOne() or run exec() on the Query object returned.

db.categoriesPCO.findOne({_id:"Nokia"}, function (err, item) {
});

However, you can't use the same while loop code to generate the path, so you'll need to use recursion instead. Something like this should work:

var path=[];

function addToPath(id, callback) {
    db.categoriesPCO.findOne({_id:id}, function (err, item) {
      if (err) {
          return callback(err);
      }
      path.push(item._id);
      if (item.parent !== null) {
          addToPath(item.parent, callback);
      }
      else {
          callback();
      }
    });
}

addToPath("Nokia", function (err) {
  path.reverse().join(' / ');
});

NB In addition, instead of pushing new items onto the end of the path array and then reversing it, you could use path.unshift() which adds the item to the beginning of the array.