properties

In our PType, when we talk about the fields of our persistent object, we talk about properties, or Props. Properties map to underlying members within the persistent object, at any depth. They follow a path from the root of the persistent object, and take on the type of that member in the persistent.

When we use the @persistent annotation, the properties are generated for us automatically. For example, if we define User as follows:

import longevity.model.annotations.component
import longevity.model.annotations.persistent

@component[DomainModel] case class Email(email: String)
@component[DomainModel] case class Markdown(markdown: String)
@component[DomainModel] case class Uri(uri: String)

@component[DomainModel]
case class UserProfile(
  tagline: String,
  imageUri: Uri,
  description: Markdown)

@persistent[DomainModel]
case class User(
  username: String,
  email: Email,
  profile: UserProfile)

Longevity will generate a User companion object that looks something like this:

import longevity.model.PType
import longevity.model.ptype.Prop

object User extends PType[DomainModel, User] {
  object props {
    object username extends Prop[User, String]("username")
    object email extends Prop[User, Email]("email")
    object profile extends Prop[User, UserProfile]("profile") {
      object tagline extends Prop[User, String]("tagline")
      object imageUri extends Prop[User, Uri]("imageUri")
      object markdown extends Prop[User, Markdown]("markdown")
    }
  }
}

So if we wanted to refer to the markdown on a User's profile, we would say User.props.profile.markdown.

You can build the properties by hand if you like, but you will need to specify both the path, and the type of the property yourself. Longevity will check that the type is correct when the DomainModel is created.

In principle, properties could map through any path from the persistent object, and have a wide variety of types. In practice, the kinds of properties currently supported is somewhat limited. We do plan to address all of these limitations, and removing some of them is high priority. For more details, please see the “remove restrictions on properties” epic on our story board. Here are there current limitations:

• No properties with collection types.
• No properties with types that (recursively) contain members with collection or polymorphic types.
• No properties with paths that contain collections.
• No properties with paths that terminate with a polymorphic type.