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Create an Anchor

Introduction​

In CDK, an Anchor definition represents a model or an overlay subset signature. An anchor is a property on the model or overlay node, and exposes one or more properties of the node. You should think of an anchor as a "representative" of the model.

A new anchor consists of a few core components,

  • Anchor is a node representing a subset of a model or overlay properties.
  • Anchor Schema defines the structure and validation rules for anchor data.

Anchors extend the AAnchor abstract class and are decorated with the @Anchor decorator. Their main purpose is,

  • Exposure of base models: It exposes a small part of the model or overlay data, allowing these models to remain unexposed from the outside world.
  • Signature: Anchors provides unique signatures for models and overlays, allowing them to be grabbed by their anchors, rather than by their properties directly.

Create an Anchor​

To create an empty anchor, Octo provides you with a simple template.

An anchor options require below information,

  • -n simple-account: specifies the name of the anchor.
  • --family aws-account: specifies the family of the anchor. The anchor will be created under this folder.
  • -t account: specifies the type of model the anchor is for. For overlays, the type is -t overlay.
  • --package @example: specifies the package name.
note

Notice how we don't prefix the names with -anchor, since the templates automatically append the names with proper suffixes.

Run this command from the root of your Octo project,

npx @quadnix/octo-build create-anchor -n simple-account --family aws-account -t account --package @example

It should produce a directory structure like this,

src/anchors/aws-account
├── simple-account.anchor.schema.ts
└── simple-account.anchor.ts

This anchor is currently empty, and we will write custom logic in these files.

Anchor Schema​

An anchor schema defines the structure and validation rules for anchor data, and will always extend from the BaseAnchorSchema.

The BaseAnchorSchema already defines the necessary fields an anchor schema must have, but the properties field is empty. You can add the properties you think your anchor needs, and optionally add validation rules for each property.

simple-account.anchor.schema.ts
override properties = Schema<{
  property1: string;
  property2: number;
}>();
tip

Most of the time, the anchor fields are derived from their parent properties.

Anchor​

An anchor always extends from the AAnchor abstract class.

The anchor class generated using the template is usually good enough to not require any customizations. The anchor schema defines the parent this anchor is associated with.

simple-account.anchor.ts
constructor(
  anchorId: string,
  properties: SimpleAccountAnchorSchema['properties'],
  parent: SimpleAccountAnchorSchema['parentInstance'],
) {
  super(anchorId, properties, parent);
}