I had a lot of trouble finding documentation for this. If you want to make a call on the main thread in RubyCocoa, the format is something like:

performSelectorOnMainThread_withObject_waitUntilDone('method_name:', object, true)

So two things that took me a while:

1. method_name has a trailing colon.
2. The object the has the method you want to call should be the second argument. I got it in my head it should be the first for some reason.

I needed to export some data from a huge data table. Iterating through MyModel.find took too long and too much ram, so I went straight to the db instead.

Example code was tough to find, so here's an example:

sql = "select * from #{ MyModel.table_name }"
MyModel.connection.execute(sql) do |handle|
  handle.fetch do |row|
    # row is an array of values
    ... export row ...
  end
end