How do I perform this query in both Mongo console and Mongoid?

I'm trying to learn how to query Mongo in more advanced ways. Let's say my data structure is this:

{ "_id" : "-bcktick-ajman-ae-292932", "asciiname" : "`Ajman", 
    "alternatenames" : [
    {
        "isolanguage" : "no",
        "alternateNameId" : 开发者_StackOverflow2698358,
        "alternateName" : "Ajman"
    },
    {
        "isolanguage" : "en",
        "alternateNameId" : 2698357,
        "alternateName" : "Ajman"
    }
  ]
}

So to find Ajman is easy:

db.cities.find({ "asciiname":"`Ajman" })

However, I want to find cities that only have an isolanguage of en. You'll notice the isolanguage is in the alternatenames array.

But I can't seem to find the correct syntax in either the client or mongoid

Either one (or both) would be greatly appreciated.

Thanks

---

I think you are looking for the $elemMatch keyword:

db.cities.find(
  { 'alternatenames' : {
       $elemMatch: { isolanguage: 'en'} 
     } 
})

Currently, Mongoid does not have a helper for $elemMatch so you have to pass in the raw query:

City.where({ :alternatenames => { '$elemMatch' => { :isolanguage => 'en' } } })

More info here on $elemMatch here:

• http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24elemMatch
• http://www.mongodb.org/display/DOCS/Dot+Notation+%28Reaching+into+Objects%29

More info on Mongoid support for $elemMatch here:

• http://groups.google.com/group/mongoid/browse_thread/thread/8648b451e3957e12
• https://github.com/mongoid/mongoid/issues/750