longevity

A Persistence Framework for Scala and NoSQL

View project on GitHub

repo.retrieve

You can look up any persistent entities from the database using the keys you defined in your PType. All you need is a KeyVal. One way to do this is to construct one yourself, like so:

val userRepo = repoPool[User]
val username = Username("smithy")
val futureUserState: Future[Option[PState[User]]] =
  userRepo.retrieve(username)

Take note that Repo.retrieve returns an optional PState, since there is never a guarantee that a KeyVal will match an existing persistent object. If you feel confident that the persistent object does exist, you can use Repo.retrieveOne instead. This is a simple wrapper method for retrieve, that opens up the Option[PState[P]] for you. If the option is a None, this will result in a NoSuchElementException.

You can also get a KeyVal from an aggregation in a related entity. For example, a BlogPost aggregates a set of authors for that post:

case class BlogPost(
  uri: BlogPostUri,
  title: String,
  slug: Option[Markdown] = None,
  content: Markdown,
  labels: Set[String] = Set(),
  postDate: DateTime,
  blog: BlogUri,
  authors: Set[Username])
extends Persistent

Let’s retrieve all the authors for a blog post:

def getAuthorsForPost(blogPost: BlogPost): Future[Seq[PState[User]]] = {
  val futures: Seq[Future[PState[User]]] = blogPost.authors.toSeq.map { author =>
    userRepo.retrieveOne(author)
  }
  Future.sequence(futures)
}

Once you get back your PState, you can of course use it to examine the persistent object itself with PState.get. You can modify it with PState.map, and you can pass the state on to Repo.update or Repo.delete.

Repo.retrieve will always result in a database call. Longevity will not cache versions for you and pull them from the cache. Not caching provides a guarrantee that the retrieved object is up to date with the latest state of the database, and reduces the chances of a write collision. We may revisit this in the future, but we do not consider it an excessive burden on the longevity user to employ their own cache, if need be.

prev: repo.create
up: repositories
next: repo.update