Rails Transaction Demonstration

rails_txn_rollback_spec.rb

require 'spec_helper'

describe 'Rails Transaction Demonstration' do

  it 'Should rollback due to any exception raised' do

    expect {

      ActiveRecord::Base.transaction do
        NotificationHistory.create!(transporter: 'should not see this')
        Resource.create(name: 'should not see this')
        NotificationHistory.first.transporter = 'should not see this'
        NotificationHistory.first.save!
        raise 'should not have create / saves persisting'
      end

    }.to raise_error

    NotificationHistory.count.should == 0
    Resource.count.should == 0
  end

  context 'Special case of ActiveRecord::Rollback exception' do

    it 'Creates objects even though Rollback is triggered in inner txn' do

      # this is created
      NotificationHistory.create!(transporter: 'first')

      expect {
        ActiveRecord::Base.transaction do

          # this is created, inner transaction rollback doesnt affect at all
          NotificationHistory.create!(transporter: 'This is created')

          ActiveRecord::Base.transaction do
            # this is created, inner transaction rollback doesnt affect at all
            NotificationHistory.create!(transporter: 'Inner transporter')
            raise ActiveRecord::Rollback
          end

        end

      }.to_not raise_error

      # 3 Objects created, reason is the ActiveRecord::Rollback exception in the nested block does not issue a ROLLBACK.
      # Since these exceptions are captured in transaction blocks,
      # the parent block does not see it and the real transaction is committed.
      NotificationHistory.count.should == 3
    end

    it 'Creates only parent objects when RollBack is triggered in inner txn' do
      # this is created
      NotificationHistory.create!(transporter: 'first')

      expect {
        ActiveRecord::Base.transaction do

          # this is created, inner transaction rollback doesnt affect parent
          NotificationHistory.create!(transporter: 'This is created')

          ActiveRecord::Base.transaction(requires_new: true) do
            # not created!
            NotificationHistory.create!(transporter: 'Inner transporter')
            raise ActiveRecord::Rollback
          end

        end

      }.to_not raise_error

      # only 2 objects created. In order to get a ROLLBACK for the nested transaction you may ask for a real
      # sub-transaction by passing requires_new: true. If anything goes wrong,
      # the database rolls back to the beginning of the sub-transaction without rolling back the parent transaction.
      NotificationHistory.count.should == 2
      NotificationHistory.first.transporter.should == 'first'
    end

  end


end