Storing Directory Hierarchy in a Key-Value Data store

Question

What is a clean/efficient method for storing the directory Hierarchy/tree in a Key-Value database (in my case MongoDB but any of them)?

For example a tree structure

Answer 1

I don't have a huge amount of NOSQL experience, so this isn't a definitive answer, but here's how I'd approach it:

I would likely use your first approach, where you have:

{
  dir: 'dir_name',
  parent_dir: 'parent_dir_name'
}

And then set up a map-reduce to quickly query the children of a directory. MongoDB's map-reduce functionality is still only available in the development branch and I haven't worked with it yet, but in CouchDB (and I assume, with a few modification, in MongoDB) you could do something like:

map:
function(doc) {
  emit( doc.parent_dir, doc.dir );
}

reduce:
function(key, values) {
  return( values );
}

Which would give you the list of sub-directories for each parent directory.