query on count of embedded documents

[robj]

one post has_many attachments

I am trying to do a query for only posts with attachments

ie, something along the lines of:

posts.where(:attachments.length.gte => 1 ).count

this of course does not work, but is there anyway to achieve this with
a criteria query without reverting to something like:

@imageable.posts.each do |post|
if post.attachments.length > 0
@posts << post
end
end



Thanks

[Durran Jordan]

Unfortunately MongoDB does not provide a length comparison of arrays in it's query language, but you could achieve it with javascript. (Note that it would result in a full scan of the collection on the db side):

Post.where("this.attachments.length > 0")

2011/10/16 robj <robert....@gmail.com>

[Nickolay Kolev]

How about creating a counter cache field (named, say, attachments_count) and update in a before_save block?

[rubish gupta]

http://stackoverflow.com/questions/6515800/can-rails-scopes-filter-on-the-number-of-associated-classes-for-a-given-field/6520882#6520882 have some answers to find out if a document has some related documents.

[robj]

Hi Rubish, that solution would work if the attachments were
referenced, but in this case they are embedded.

I will go with the counter cache field as described by Nickolay, as id
like to keep this a criteria query so I can still simply use
pagination.

Thanks all


On Oct 17, 8:54 pm, rubish gupta <rubish.gu...@almaconnect.com> wrote:
> http://stackoverflow.com/questions/6515800/can-rails-scopes-filter-on...

[Jeffrey Jones]

Seems really crappy that you cannot easily check the size for embedded
documents since they...well, they are embedded!

Maybe submit a feature request to 10gen?

[Durran Jordan]

There already is an open issue for this:

https://jira.mongodb.org/browse/SERVER-1474

2011/10/19 Jeffrey Jones <jjo...@toppan-f.co.jp>