How do I rename a collection with Mongoid 7.x and MongoDB 3.x

Question

I have a test app using Ruby 2.2.2 and am using Mongoid 7.0.0 and Moped 1.5.3 with MongoDB 3.6.2 - we are upgrading an ancient codebase using Mongoid 4.x and MongoDB 2.6 and found numerous breaking-changes in the API along the way

The most serious is we used to be able to do SomeModel.collection.rename however this API method now no longer exists (to my knowledge) and gives an undefined error

I've also tried the following:

Mongoid.default_client.command({ renameCollection: "test.some_collection", to: "test.some_collection2", dropTarget: true })

However this returns

Mongo::Error::OperationFailure: renameCollection may only be run against the admin database. (13)

From a command shell however, I'm able to issue:

db.some_collection.renameCollection("some_collection2") 

And this works - this seems to be my only last recourse from what I can see, how would I issue this as a Moped command? (I'm not overly familiar with the syntax scheme)

Also, any reason why such a seemingly straightforward operation is apparently not exposed by Mongoid?

Answer 1

So found a way to do it - some of my collections are stored on different databases

# returns a hash of client config from mongoid.yml eg ["secondary_db", { "database" => "myDB", hosts => [xxx, xxx, xxx] }]
cfg = Mongoid.clients.select { |k,v| Mongoid.clients[k][:database] == MyModel.storage_options[:database] }.first 

# now create a new Client instance using the right database
client = Mongo::Client.new(cfg[1]["hosts"], { database: cfg[1]["database"]})

client.command("$eval" => "db.my_collection.renameCollection('new_col_name')")