How to search against a deep tree-like structure in MongoDB?

Question

The simplest way to explain my situation is with standard filesystem structure which is close to what I want to accomplish:

Folder A
- Folder A2
-- File 1
-- File 2
- File 3
Folder B
- Folder B2
- Folder B3
-- File 4

Folder has fields:

- _id
- parents (in my case there can actually be multiple!)

File has fields

- _id
- targetFolder

So, basically a file could be very deep in the hierarchy.

How do I search and structure my DB efficiently so that I can have deep folder hierarchies, with any of them having files.

I want to be able to do a query that returns every file under e.g. Folder A. How could I do this?

Answer 1

I recommend the MongoDb official documentation of this topic. Storing trees in database is non trivial and every solution have its pro and cons. I experienced successfully materialized paths model, which is very efficient on hierachy search but expensive on tree modification because you have to update every descendant node.

Answer 2

Not store them as a tree in mongo, at all! Like Lucas said, here is a good explanation on how you do it. But your problem is that you need a chained join from the root to Folder A. You could do something like:

{ _id, name, type, parent: { grandparent : { parentOfGrandparent : {..........

So to search for all files of Folder A you search for all files that parent is "Folder A". I think this will work:

db.files.find( { parent : { "Folder A : { $exists: true } } } );