Question

If my stored document looks like this:

doc = {
    'Things' : [ 'one' , 'two' , 'three' ]
    }

How can I query for documents which contain one in Things?

I know the $in operator queries a document item against a list, but this is kind of the reverse. Any help would be awesome.

Answer 1

Use MongoDB’s multikeys support:

MongoDB provides an interesting “multikey” feature that can automatically index arrays of an object’s values.
[…]

db.articles.find( { tags: 'april' } )
{"name" : "Warm Weather" , "author" : "Steve" , 
 "tags" : ["weather","hot","record","april"] , 
 "_id"  : "497ce4051ca9ca6d3efca323"}

Basically, you don’t have to worry about the array-ness of Things, MongoDB will take care of that for you; something like this in the MongoDB shell would work:

db.your_collection.find({ Things: 'one' })