Fast related tag search in MongoDB

Question

I've got two document sets:

Wikis and WikiTags. Since i want flexible editing of tag names I don't want to embed tag itself into wiki document. So, I store a list of wiki_tag_ids inside wiki document.

I wonder what is the best way to find related tags using this schema. By related tags I mean tags that exist in other wikis tagged with selected tags.

May be I should store related tags in WikiTag document?

Answer 1

I suggest you should store to store WikiTag in Wiki document. Mongodb allow easy update, delete single document from nested collection, thats mean 'flexible editing of tag names'.

Collection like this:

wikis 
  {
    _id,
    wikiTags {_id, name, ...},
    ...
  }

So, for example if you want update nested WikiTag name with id = SomeTagId you can:

db.wikis.update( {'wikiTags.id':SomeTagId},
                 {$set:{'wikiTags.$.name':"New Tag Name"}},
                  false, 
                  true )

If yoy want delete item from nested array you should use $unset, add new item: $push, $addToSet

So, i guess now you see that any operation with nested array can be done easy. And if performance is an issue -- use embedding.

Hope this helps.