Question

I have two collections: news and subscribes. Every news item has an array of strings – “tags”. Every subscribe also has such “tags”.

Subscribe’s news items are items having all tags that subscribe has, and may be more. News item’s subscribes are subscribes having any of this item’s tags, but no any more.

When I want to get a Subscribe’s news, I’m doing such request on Ruby MongoID:

NewsItem.where(:tags.all => @subscribe.tags)

How can I get all subscribes for some news item?

For example:

item.tags = ["foo", "bar"]

subscribe1.tags = ["foo"]
subscribe2.tags = ["bar"]
subscribe3.tags = ["foo", "bar"]
subscribe4.tags = ["foo", "bar", "baz"]

item.subscribes should give subscribes 1..3, but subscribe4 should not be included, because it has a “baz” tag that is not included in item.tags

Answer 1

Based on your description, you don’t really want an $all. Instead, you are looking for some form $subset operator. There is JIRA request for just such a thing, however it is not implemented at this time.