Documentation about request_migrations

[ezekg]

Thanks for the feedback. You're correct that this is for applying transformations on business logic, which allows for breaking changes to be made to a code base while maintaining backwards compatibility with older clients.

In the case of the migrate method, data is whatever you provide to migrate! within a request or response migration. It could be a hash (parsed JSON payload), an HTML string, an XML string, etc. — it's entirely dependent on input.

And the data in type: 'user' line is using pattern matching to match against the input data. The lambda will return true if data matches the pattern, i.e. it's a hash containing a key type with value 'user'.

You could very well write it without pattern matching as follows:

migrate if: data -> { data[:type] == 'user' } do |data|
  # data is a hash with type user
end

I'll spend some time and update the docs soon.