Question

I am creating a REST API in rails. I’m using RSpec. I’d like to minimize the number of database calls, so I would like to add an automatic test that verifies the number of database calls being executed as part of a certain action.
Is there a simple way to add that to my test?
What I’m looking for is some way to monitor/record the calls that are being made to the database as a result of a single API call.
If this can’t be done with RSpec but can be done with some other testing tool, that’s also great.

Answer 1

The easiest thing in Rails 3 is probably to hook into the notifications api.

This subscriber

class SqlCounter< ActiveSupport::LogSubscriber

  def self.count= value
    Thread.current['query_count'] = value
  end

  def self.count
    Thread.current['query_count'] || 0
  end

  def self.reset_count
    result, self.count = self.count, 0
    result
  end

  def sql(event)
    self.class.count += 1
    puts "logged #{event.payload[:sql]}"
  end
end

SqlCounter.attach_to :active_record

will print every executed sql statement to the console and count them. You could then write specs such as

expect do
  # do stuff
end.to change(SqlCounter, :count).by(2)

You’ll probably want to filter out some statements, such as ones starting/committing transactions or the ones active record emits to determine the structures of tables.