Question

I have a collection with a subdocument tags like :

Collection News :
   title (string)
   tags: [tag1, tag2...]

I want to select all the tags who start with a pattern, but returning only the matching tags.

I already use a regex but it returns all the news containing the matching tag, here is the query :

db.news.find( {"tags":/^proga/i}, ["tags"] ).sort( {"tags":1} ).
    limit( 0 ).skip( 0 )

My question is : How can I retrieve all the tags (only) who match the pattern ?
(The final goal is to make an autocomplete field)

I also tried using distinct, but I didn’t find a way to make a distinct with a find, it always returning me all the tags 🙁

Thanks for your time

Answer 1

Embedded documents are not collections. Look at your query: db.news.find will return documents from the news collection. tags is not a collection, and cannot be filtered.

There is a feature request for this “virtual collection feature” (SERVER-142), but don’t expect to see this too soon, because it’s “planned but not scheduled”.

You can do the filtering client-side, or move the tags to a separate collection. By retrieving only a subset of fields – only the tags field – this should be reasonably fast.

Hint: Your regex uses the /i flag, which makes it impossible to use indexation. Your db strings should be case-normalized (e.g. all upper case)