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Transactional before all with RSpec and DataMapper

By default, before(:all) in rspec executes outside of any transaction, meaning that you can’t really use it for creating objects. Normally this should go in a before(:each), but for a spec with simple creation and a large number of assertions this is terribly inefficient.

Let’s fix it!

This code assumes you are using DataMapper, and that your database supports some form of nested transactions (at the very least faking them with savepoints – see nested transactions in postgres with datamapper). It wraps each before/after :all and :each in it’s own transaction.

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RSpec.configure do |config|
  [:all, :each].each do |x|
    config.before(x) do
      repository(:default) do |repository|
        transaction = DataMapper::Transaction.new(repository)
        transaction.begin
        repository.adapter.push_transaction(transaction)
      end
    end

    config.after(x) do
      repository(:default).adapter.pop_transaction.rollback
    end
  end

  config.include(RSpecExtensions::Set)
end

See that RSpecExtensions::Set include? That’s a version of the lovely let helpers that works with before(:all) setup. Props to pcreux for this:

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module RSpecExtensions
  module Set

    module ClassMethods
      # Generates a method whose return value is memoized
      # in before(:all). Great for DB setup when combined with
      # transactional before alls.
      def set(name, &block)
        define_method(name) do
          __memoized[name] ||= instance_eval(&block)
        end
        before(:all) { __send__(name) }
        before(:each) do
          __send__(name).tap do |obj|
            obj.reload if obj.respond_to?(:reload)
          end
        end
      end
    end

    module InstanceMethods
      def __memoized # :nodoc:
        @__memoized ||= {}
      end
    end

    def self.included(mod) # :nodoc:
      mod.extend ClassMethods
      mod.__send__ :include, InstanceMethods
    end

  end
end

Fast specs make me a happy man.

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