A phantom type for annotating DBIOActions with specific effects (e.g. Write or
Transactional). Effects can be composed through intersection types (e.g.
Write with Transactional. The standard Slick back-ends do not restrict the evaluation of
actions based on effects but they can be used in user-level code (e.g. for ensuring that all
writes go to a master database but reads can also be performed by a slave).
Write with Transactional