anchor.diff:    config.to_prepare do
       Rails.configuration.event_store = RailsEventStore::Client.new(
         mapper: RubyEventStore::Mappers::Default.new(
  -        serializer: JSON
  +        serializer: Marshal
         )
       )
     end
  
positive.code: 
  Check out the code of our [mappers](https://github.com/RailsEventStore/rails_event_store/blob/master/ruby_event_store/lib/ruby_event_store/mappers/) and [transformations](https://github.com/RailsEventStore/rails_event_store/blob/master/ruby_event_store/lib/ruby_event_store/mappers/transformation/) on github for examples on how to implement mappers & transformations.
  
  You can pass a different `mapper` as a dependency when [instantiating the client](/docs/install).
  
  ```ruby
  # config/environments/*.rb
  
negative.code: end
  
  OrderPlaced = Class.new(MyEvent)
  </code>
  </pre>
  </div>
  
  That shields you from data keys being transformed from symbols into strings. It doesn't do anything with data values associated to those keys.
  
  <div class="highlight">
  <pre class="syntax-highlight ruby">
  <code>
  event_store.publish(OrderPlaced.new(event_id: 'e34fc19a-a92f-4c21-8932-a10f6fb2602b', data: { foo: :bar }))
  event = event_store.read.event('e34fc19a-a92f-4c21-8932-a10f6fb2602b')
  
  