Mastering Functional Programming

Database layer

A database layer is implemented in terms of the Doobie library. Each entity has a separate Scala file, where there is a singleton object, which has all of the methods that we need for the purposes of this application. For example, let's take a look at the API that the customer object exposes:

object customer extends CustomerDbHelpers {  def create(c: Customer): IO[Int] = ???  def findByName(name: String): IO[Option[Customer]] = ???  def list: IO[List[Customer]] = ???  def get(id: Int): IO[Customer] = ???  def update(c: Customer): IO[Int] = ???  def delete(id: Int): IO[Int] = ???}trait CustomerDbHelpers {  val selectCustomerSql = fr"select * from customer"  // to be explained further in the chapter}

So, we have several database access ...