Data Client Schema

1. Defining Schemas

Define schemas to represent the JSON returned by an endpoint. Compose these to represent the data expected.

Object

• Entity - represents a single unique object (denormalized)
• EntityMixin - turn any pre-existing class into an Entity
• new Union(Entity) - polymorphic objects (A | B)
• {[key:string]: Schema} - immutable objects
• new Invalidate(Entity|Union) - to delete an Entity
• new Lazy(() => Schema) - break circular imports / defer deep recursive denormalization

List

• new Collection([Schema]) - mutable/growable lists
• [Schema] - immutable lists
• new All(Entity|Union) - list all Entities of a kind

Map

• new Collection(Values(Schema)) - mutable/growable maps
• new Values(Schema) - immutable maps

Lens-dependent entity fields

• new Scalar({ lens, key, entity? }) - fields that vary by runtime lens (portfolio, currency, locale) without entity mutation

Derived / selector pattern

• new Query(Queryable) - memoized programmatic selectors

  const queryRemainingTodos = new Query(
    TodoResource.getList.schema,
    entries => entries.filter(todo => !todo.completed).length,
  );
  

  const groupTodoByUser = new Query(
    TodoResource.getList.schema,
    todos => Object.groupBy(todos, todo => todo.userId),
  );
  

  Define Query transformations with the data model (e.g. src/resources/) — not inside custom hooks wrapping useSuspense/useQuery, which hides data dependencies and couples data logic to view code.

2. Entity best practices

• Every Entity subclass defines defaults for all non-optional serialised fields.
• Override pk() only when the primary key ≠ id.
• pk() return type is number | string | undefined
• Override Entity.process(value, parent, key, args) to insert fields based on args/url
• static schema (optional) for nested schemas or deserialization functions
  • When designing APIs, prefer nesting entities

3. Entity lifecycle methods

• Normalize (JSON response → cache): operates on POJOs; output is JSON-serializable plain data stored in the normalized cache. Order: process() → pk() → validate() → visit nested schemas (recurse into schema fields) → if existing: mergeWithStore() which calls shouldUpdate() and maybe shouldReorder() + merge(); metadata via mergeMetaWithStore().
• Denormalize (cache → component): creates Entity class instances via fromJS(), restoring prototype chain so getters, methods, and schema processing work. Order: createIfValid() → validate() → fromJS() → unvisit nested schemas (recurse into schema fields).

4. Union Types (Polymorphic Schemas)

To define polymorphic resources (e.g., events), use Union and a discriminator field.

import { Union } from '@data-client/rest'; // also available from @data-client/endpoint

export abstract class Event extends Entity {
  type: EventType = 'Issue';    // discriminator field is shared
  /* ... */
}
export class PullRequestEvent extends Event { /* ... */ }
export class IssuesEvent extends Event { /* ... */ }

export const EventResource = resource({
  path: '/users/:login/events/public/:id',
  schema: new Union(
    {
      PullRequestEvent,
      IssuesEvent,
      // ...other event types...
    },
    'type', // discriminator field
  ),
});

5. Collections (Mutable Lists & Maps)

Collections wrap Array or Values schemas to enable mutations (add/remove/move).

pk routing

pk() uses nestKey(parent, key) when nested in an Entity and available; otherwise it uses argsKey(...args), then serializes the result. Without options, it defaults to argsKey: params => ({ ...params }), using all endpoint args as the collection key.

• argsKey — derive pk from endpoint arguments (default)
• nestKey — derive pk from parent entity for nested shared-state collections

Define both on the same Collection to reuse one definition top-level and nested. When argsKey(args) and nestKey(parent) produce the same object shape, the top-level fetch and the nested read resolve to the same (referentially equal) array/map — push/unshift/assign/move/remove on either updates both:

const userTodos = new Collection([Todo], {
  argsKey: ({ userId }: { userId?: string }) => ({ userId }),
  nestKey: (parent: User) => ({ userId: parent.id }),
});

nonFilterArgumentKeys

Default createCollectionFilter uses nonFilterArgumentKeys (default: keys starting with 'order') to exclude non-filter args when matching collections. This affects which existing collections receive new items from push/unshift/assign/move.

Override as function, RegExp, or string[]:

new Collection([Todo], { nonFilterArgumentKeys: /orderBy|sortDir/ })

Extenders

All usable with ctrl.set() (local-only) or via RestEndpoint extenders (network).

6. Supplementary Endpoints (enrich existing entities)

When an endpoint returns partial or differently-shaped data for an entity already in cache (e.g., a metadata endpoint, a stats endpoint, a lazy-load expansion endpoint), use the same Entity as the schema — don't create a wrapper entity.

See partial-entities for patterns and examples.

7. Best Practices & Notes

• Always set up schema on every resource/entity/collection for normalization
• Normalize deeply nested or relational data by defining proper schemas
• Use Entity.schema for client-side joins
• Use Denormalize<> type from rest/endpoint/graphql instead of InstanceType<>. This will handle all schemas like Unions, not just Entity.

8. Common Mistakes to Avoid

• The normalized cache stores plain JSON-serializable objects (POJOs), not class instances.
• Don't forget to use fromJS() or assign default properties for class fields — bare TS field types emit no runtime defaults, so schema inference breaks
• Manually merging or 'enriching' data; instead use Entity.schema for client-side joins

References

For detailed API documentation, see the references directory:

• Entity - Normalized data class
• EntityMixin - Turn any class into an Entity
• Collection - Mutable/growable lists
• Union - Polymorphic schemas
• Query - Programmatic selectors
• Invalidate - Delete entities
• Lazy - Deferred / circular schemas
• Scalar - Lens-dependent entity fields
  • Scalar demo
• Values - Map schemas
• All - List all entities of a kind
• Array - Immutable list schema
• Object - Object schema
• schema - Schema overview
• relational-data - Relational data guide
• computed-properties - Computed properties guide
• partial-entities - Partial entities guide
• side-effects - Side effects guide
• sorting-client-side - Client-side sorting guide