Finding all embedded documents

[graf.otodrakula]

Hello guys and gals.

My data model is:

class User
include MongoMapper::Document
many :posts
end

class Post
include MongoMapper::EmbeddedDocument
end

Is there any way to fetch all Posts of all Users?

P.S. User.all.map(&:posts).flatten sounds really slow.

[John Nunemaker]

I would not embed posts in user. Posts will grow over time and most likely need to be larger than 4mb doc limit in mongo. Make Post a document and add key :user_id, ObjectId to Post model.

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[graf.otodrakula]

Thank you for your fast reply.

I completely understand the tradeoffs of embedding posts into User.
However, it's more an example than a real-world architecture.
The question is how to find an embedded document by specific criterion
or criteria, in my case, find a post by id. As far as I can see in
embedded_document.rb there's no #first method defined. So, the answer
might be going into mongo-ruby-driver internals and doing something
like User.collection.find({ "posts.id" =>
"4b9130ea37a08e6477000002" }), however, it returns Cursor object with
#count == 0. Am I missing something?

On Mar 6, 9:34 pm, John Nunemaker <nunema...@gmail.com> wrote:
> I would not embed posts in user. Posts will grow over time and most likely
> need to be larger than 4mb doc limit in mongo. Make Post a document and add
> key :user_id, ObjectId to Post model.
>
> On Sat, Mar 6, 2010 at 8:57 AM, graf.otodrakula

> <graf.otodrak...@gmail.com>wrote:

[John Nunemaker]

There is a find method that works with single id. Other than that, just use Enumerable http://ruby-doc.org/core/classes/Enumerable.html to get what you need.

[Stephen Eley]

On Mon, Mar 8, 2010 at 3:28 AM, graf.otodrakula
<graf.ot...@gmail.com> wrote:

> So, the answer
> might be going into mongo-ruby-driver internals and doing something
> like User.collection.find({ "posts.id" =>
> "4b9130ea37a08e6477000002" }), however, it returns Cursor object with
> #count == 0. Am I missing something?

The problem there could be that the string "4b9130ea37a08e6477000002"
isn't really the id. The id is a Mongo::ObjectId. So
User.collection.find_one({ "posts.id" =>
Mongo::ObjectId.from_string("4b9130ea37a08e6477000002") }) might work.

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Have Fun,
Steve Eley (sfe...@gmail.com)
ESCAPE POD - The Science Fiction Podcast Magazine
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[Ckhrysze]

What about something like

User.collection.mapreduce(map_func, reduce_func)

where the functions are:

map_func = <<-JS
function() {
this.posts.forEach( function(post) {
emit(post._id, post);
})
}
JS

reduce_func = <<-JS
function(k,v) {
return v[0];
}
JS

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