Type Members

1.  type Migration[T] = (T) ⇒ T

   A Migration[T] is a simple type alias for a function that takes a T and produces another T, usually the input value transformed in some way in order to make it compatible with a higher version.

2.  implicit final class MigrationWithComposition[T] extends AnyVal

   Adds support for combining two instances of Migration[T] into a new Migration[T] that will apply the first one and then the second one.

3.  class Migrator[R, V <: Version] extends AnyRef

   A Migrator[R, V] can migrate raw values of type R from older versions to version V by applying a specific Migration[R] to it.

   A Migrator[R, V] can migrate raw values of type R from older versions to version V by applying a specific Migration[R] to it.

   You can create instances of Migrator[R, V] by using a small type-safe DSL consisting of two parts: the from[R, V1] function will create a Migrator[R, V1] and then you can use the to[V](migration: Migration[R]) function to build instances that can migrate multiple versions.

   R

   The type of raw data being migrated. In the JSON implementation this would be JsValue.

   V

   The "current" version of this Migrator, i.e. it can migrate values from V1 to this version or any version in between.

   Example:

   1. Using the json implementation:

      val p = persister[CartCreated, V3]("cart-created",
        from[JsValue, V1]
          .to[V2](_.update('cart / 'items / * / 'price ! set[Int](1000)))
          .to[V3](_.update('timestamp ! set[Long](System.currentTimeMillis - 3600000L)))
      )

4.  case class UndefinedMigrationException(fromVersion: Int, toVersion: Int) extends RuntimeException with Product with Serializable

   Runtime exception for signalling that the specified migration path is not supported.