Question

I’m looking for the mongoid equivalent to:
How to select the comparison of two columns as one column in Oracle

I can’t seem to find any documentation or examples comparing columns within the same query. Is this just not possible in Mongoid?

Answer 1

Nope, you need to drop down to the mongodb ruby driver to do this and it will potentially be very slow as it is a javascript query that will not use an index:

Model.collection.find_one({"$where" => 'this.name == this.name2'})

Which is equivalent to third shell command here.:

> db.collection.insert({name: "awesome", name2: "awesome"})
> db.collection.insert({name: "awesome", name2: "awesome2"})
> db.collection.find('this.name == this.name2')
{ "_id" : ObjectId("xxx"), "name" : "awesome", "name2" : "awesome" }
> (line shown to signify end of results)

Note: if a document does not have key name and that same document also does not have key name2 that this will return true because null == null.